PRINCIPLES OF CHEMISTRY II
PRINCIPLES OF CHEMISTRY II CH 302
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This 143 page Class Notes was uploaded by Brady Spinka on Monday September 7, 2015. The Class Notes belongs to CH 302 at University of Texas at Austin taught by Staff in Fall. Since its upload, it has received 42 views. For similar materials see /class/181882/ch-302-university-of-texas-at-austin in Chemistry at University of Texas at Austin.
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Why is there equilibrium If the right handside of the reaction is lower in free energy why not all products If the left handside of the reaction is lower in free enrgy why not all reactants Entropy of mixing gives the mixture a slightly lower free energy than either extreme some product reactants will always be lower in G than all of one or the other Principles of Chemistry II mmmm This is only true to compounds that mix gases and solutions As a result solids and liquids do not appear in the equilibrium expression Principles of Chemistry II ownean For example CaCO3s gt COs COzg No CaCOa or CaO they are solids K PCOZ for equilibrium you must have some soi but the amount doesn39t matter Hzoa gt Haq OHaq K HOH39 Wis dissolved in water No H20 its a liquid Principles of Chemistry II mmmm The simplest of all equilibria Solubility Mxs gt Maq Xaq K MX39 special name solubility product Ksp MX39 Principles of Chemistry II ownean Easy to solve MXzs lt gt Maq 2Xaq For the following reaction ARG 542 kJ molquot at 298K lfl start out with a contain that has a pressure of l atm of H2g and l atm of F2g at equilibrium what will the partial pressure of HFg be R M X H2g F2g 2HFg I O 0 none in solution A approximately I atm C x 2x none In solution K IS really really big B approximatley 0 atm to completion E X 2X equilibrium is easy C approximately 2 atm KSP M X12 X2X 2 4X3 D approximately 4 atm E there is no way to know F rincipius of Chemistry Ii mm Principles of Chemistry II omm For the following reaction ARG 740 kJ molquot at 298K lfl start out with a contain that has a pressure of l mole of Fean at equilibrium how much solid Fe will I have For the following reaction what is the change value for H20 2C2H5g 702g gt 4C02g 6H20g R Csz 02 C02 H20 Fe203s gt 2Fes 32Ozg 0 4 LB 0 C 2X 7 7 7 A approximately 0 moles B a roXimatle l moles A 2gtlt PP y K IS really really small C approximately 2 moles N no products B 2gtlt D approximately 32 moles C 3gtlt E there is no way to know D 6gtlt Principles of Chemistry II mm Principles of Chemistry II omm 2C1H5g 702g gt 4CO 2g 6H20g CzHa 02 C02 H20 I 0 4 5 7 T 025 84x 28 For this reaction which has a higher entropy H20 gt Haq OH39aq l A the products B the reactants C theyare the same For this reaction which has a lower enthalpy H20I gt Haq OH39aq For this reaction which has a lowerfree energy H200 gt Hwaq OHaq A the products 13 the reactants C they are the same A the products B the reactants C they are the same LiClUld water In water what is the concentration of H will spontaneouslyquot dissociate to arsmall extent H20 Haq OHaq H200 lt gt Haq 0H39aq iltw HOH 0quot4l KwrHOH39 W4 Pure Water pH Log scale H OH Useful when dealing with very39small I O O or very large number big ranges of numbers every quotpHquot unit is l0X larger or smaller H C x x E x x Kw 0quot4 HOH39 XXX X W HOH390397 pH 344 IO2 M pH 2 IM 0 M linear H 0quotM pH l l l l l l l l I I 0398 0397 0395 0395 0quot 0395 0394 0393 0392 IOquot IM Acids and Bases Bronsted Lowry De nition Acid is a proton H donor Base is a proton H acceptor pH8 log H pH0 Principles of Chemistry II Vandenaout Principles of Chemistry II ovandenaout For example pH of pure water at 25 C Hydrochloric Acid HCI X I0397 HquotOH390397 pH ogHog0397 7 Neutral Acidic Basic HOH39 HgtOH39 HltOH39 at 25 C at 25 C at 25 C pH 7 pH lt 7 pH gt 7 pOH7 pOHgt7 pOHgt7 Principles of Chemistry II Vandenaout Principles of Chemistry II ovandenaout H20 gt Haq OH39aq This reaction is endothermin Given that informatiOn what do you think the pH is for pun efwaterat 60 C Lecture 15 Complex Equilibria What to do when assumptions aren39t okay To this point in creating acid base equilibria we have made our lives simple by working with compounds and amounts that reduce calculations to 4 forms H1 C H1 Kacaf z H1 KamaCb H1 Kal K32 To do this we either used monoprotic acids and bases with K values between 10394 and 1010 or we used polyprotic acids with well separated K values in that K range And we always used high concentrations like C 01M Armed with these two simple approximation ideas high C and K far apart we could do a lot of water chemistry problems very simply But these approximations don t always work For example we couldn39t work problems like 0 What is the pH of 01M sulfuric acid Reason KS too close 0 What is the pH of 01M HClOZ Ka10392 Reason Ka too close to strong acid case 0 What is the pH of 01M CH3OH Ka103914 Reason Ka too close to Kw 0 What is the pH of 10398M HCl or 10398M NaOH Reason C too small so KW matters To illustrate consider the problem if 7 01 M H2304 this should be a strong acid case but there are multiple sources of PF from three dissociations HgtHso439gt H5604 2 14 Kal 2 H2804 infinity Ka2 H8047 11 x 10 KW H OH 1 x 10 and while we can ignore the H from Kw we can t ignore the PF from the Kaz and simply use H Ca if this was a simple strong acid case like 01M HBr 7 01M HClOZ this should be a weak acid case but while we can ignore KW because it is far from Ka10392 we can t make the assumption that yields HKC12 and instead must use the quadratic solution from the RICE expression H 9 4 H 9 9 39 1 1 1 can39t eliminate because X X X X H2 the proton dissociation K3 amount is too large C x x x 2 cmm 7 01M CH3OH this should be a weak acid case but the Ka and KW are too close so we have to consider both the methanol as a weak acid and the water as a weak acid at the same time have to use e uation with K K in addition to q a W KW 103914 2 approximately equal sources of H means K HOH 1044 simultaneously a 10398 M HCl this should be a strong acid case but the C is so small that the H from KW is significant and we must consider the HOH39 KW equilibrium General treatment of all chemical equilibrium how to get exact solutions to equilibrium problems no matter how complicated the system if you can do a little math The basic idea for finding solutions borrow from something you learned to do way back in middle school solving a series of simultaneous equations For example if you know how to solve the following problem Findxandyfor 3x4y13 2x 43y 11 remember all that back substitution stuff then you can do complex equilibrium problems in a remarkably straightforward manner The recipe for complex equilibria problems 0 identify the number unknowns in the system 0 create a number of equations involving those unknowns from mass balance charge balance and equilibrium equations 0 solve the series of equations for the unknowns That s it simple as pie But what are the equations we use They must contain only known constants like known K values or starting concentrations like CHA and some subset of the unknowns equilibrium concentrations There are 3 kinds of equations we can create 0 equilibrium equations like Ka1 HA or KW HOH39 HA Note that in water equilibria the KW equation is always used Also note that mono di and triprotic acids have one two and three equilibrium equations to use 0 mass balance equations in which some known starting amount of analytical material is equated to all the forms it can make at equilibrium in solution for example when as add H3PO4 to solution all the P04quot3 can be found in one of four equilibrium forms 2 3 CH3PO4H3PO4H2PO4 HPO4 PO4 The amount of an atom in solution must equal the amount you start with Here all the P in H3PO4 has to become 0 charge balance equation in which we assume the solution is electrically neutral and that all of the cation concentration are placed on one side and must equal all the anions placed on the other side If OH39H2PO4392HPO439 3 1304 3 1 v only in solution all the sources in solution Note that we put coefficients in front of the multiply charged anions to weight the extra charge each provides So now that we have a bunch of equations what do we do Find their simultaneous solutions The engineers and those with a little linear algebra background know all about setting up giant matrices to crank out solutions for n unknowns and n equations The rest of us will do a bunch of clunky substitutions to get our answers or just approximate to death Example 01M HCl in H20 has 3 unknown concentrations H OHquot Cl39 so set up 3 simultaneous equations and solve Example 01M H3PO4 in H20 has 6 unknown concentrations H3PO4 HZPO439 HPO4392 PO4393 H OHquot so set up 6 simultaneous equations and solve Example What is the H OH39 HZCO3 HCO339 CO339 when I toss 1 X 10394 moles HZCO3 in IL of solution I have 5 equations to solve for 5 unknown concentrations Let s take this one all the way and write down all the equations Equation 1 Mass balance CHZCO3 H2CO3 HCO3 CO3 H J Amounr of carbonate 1 add to H20 all the forms of C03 in solution Equation 2 Charge balance H OH HCO3 2CO3 f all the an the KWH 0H391x103914 Equation 3 q q K31 H HC03 equ111br1urn Equation 4 equations K32 H2CO3 H co 392 Equatlon 5 39 l b39i quot39 3 5 equations 5 unknowns We can solve Of course no general chemistry course will make you solve this set of equations But the point is that you can All you need to know is how to find a source of equations Applying the general equilibrium treatment to a couple of our favorite systems 7 Strong acid case works at every concentration of strong acid including dilute cases Example What is the pH of 8x10398M HCl Answer There are 3 unknowns H OHquot Clquot So there are 3 equations 1 IltWH0H391x103914 e equilibrium equation 0 2 HCl39OH39 6 charge balance equation 3 CHc1Cl39 6 mass balance equation Now let39s do some back substitutions to get a simple equation with one unknown H Substitute 3 9 2HCHc1OH39 substitute 2 9 1 KwHHCHc1 and rearranging to a quadratic H2 HCHc1 KW 0 6a quadratic to find H exactly Wow the exact solution for a strong acid when you don t want to or can t use H Ca So for CHCl 8x108 M and 1ltW1x103914 H2 H8x10398 1x103914 0 yields H15x10397 pH 682 Recall we did this problem earlier using common sense What is the pH of 8x108 M HCl 709 lt no it is basic and HCl is acidic 796 lt no it is basic and HCl is acidic 682 lt only possible answer since it must be slightly less than pH 7 7 lt no it is neutral and HCl is acidic 156 lt no 8x10398M is very dilute pH is near 7 QOU QD 7 Weak acid case works at every concentration or Ka for weak acid including dilute cases Remember the slacker equation for a weak acid is KCO 5 what is the true answer For a monoprotic weak acid in solution we have 4 unknowns H OH39 HA Al so we need 4 equations mass balance CHA HA Aquot charge balance H Aquot OHquot Ka Ka HA39HA KW Kw HOH39 Without sweating the details we can back substitute to get a cubic solution in terms of if you lonely types should do this with me on Friday night H3 KatHu2 Kw KaCHAMHu KaKw 0 So that is the truthnote that in the cubic if we ignore KW we get our friend the quadratic and if CgtH we get KC12 H which is the approximations we have used to a weak acid when C is large and K is far away from others So now let s do a calculation What is the pH of 1x10 4 M phenol if Ka13x103910 Solving a cubic on your handy graphing calculator yields pH 68 for the 10394M phenol solution That was quite a lot of work to find out that dilute weak acids have a pH of just under 7 But at least we know it exactly And is we want we can use a cubic to get the exact answer while everyone else is getting kind of a right answer using the KCO 5 equation This is why engineers get to feel superior they use higher order polynomials to solve their problems Which has a lower Enthalpy Which has a higher Entropy A liquid iron B solid iron lt C they are exactly the same D it depends on the temperature A liquid iron lt B solid iron C they are exactly the same D it depends on the temperature Principles of Chemistry II ems Bout Fmimeiplas 0f ll Vanaen Bout Which has a lower Gibb39s Free Energy A liquid iron B solid iron C they are exactly the same D it depends on the temperature lt P meiples of Chemistry II ems Bout Equilibria Balance between stability of lower Enthalpy energy amp higher Entropy Physical Equilibria Phase transitions no quotchemistryquot State with the lowest free energy is most stable G H TS therefore at high temperature the state with highest S will be the most stable Principles of Chemistry ll 1an non little bit of liquid Vapor pressure 7 7 Rate of Vapor 760 736 760 695 760 215 evaporation pressure 24 ten 65 torr 545 orr A R R 0 Vacuum H20 C2H50H CZH5JZO a or vapor vapor D A 5 4 Rates are equal Rate of beyond this time condensation equilibrium vapor Pm 760 1 pressure is attained Comparing different liquids what matters is the free energy of the Enthalples Of vaponzatlon vapor compared to the liquid Water 4065 kJ molquot 1 For almost all substances the difference in ammolnl39zah ZziZSkkJ mill ENTROPY between the vapor and the liquid 39et y t er 39 J mo I is the same Methane 8l9 kJ mol39 Methanol 378 k mol39I Ethanol 385 kJ molquot 475 kJ molquot 56 kJ molquot Asvap mOII Therefore the diversity in liquids properties is dominated by the ENTHALPY of vaporization Why does butanol C4H90H have a lower vapor pressure than methanol CH3OH it has a higher entropy it has stronger inter molecular forces it has a lower molecular weight it has a higher density J 0 Boiling polnl C 7100 Why is the boilng point of H2Te higher than H2Se H2Te has a larger dipole ste has more dispersion forces H2Te has more dispersion forces BothA amp C Intermolecular forces lead to the enthalpy difference between the liquid and the vapor The larger the IMF the larger the AHVaP The larger the AHvap the smaller the vapor pressure The the smaller the vapor pressure the higher the boiling point Before we get to boiling let39s look at how different properties affect vapor pressure Lecture 22 Polymers and Biopolymers In the previous lecture we learned that by using carbon as the primary backbone we can create a seemingly endless array of molecules built on covelent bonds to carbon The simple concepts we learned at the beginning of the year about bondingilike structures being formed based on the number of valence electrons and the stability of filled shells make it possible to rationalize why different structures are possible We can even rationalize the reactivity that occurs by applying simple concepts like electronegativity or more sophisticated concepts in thermodynamics What should be most impressive is just how many different kinds of even relatively small molecules molecular weights of a few hundred we can build using carbon backbones and attaching all manner of functional groups In fact most of the compounds we take for granted in our daily lives like vitamins and medications and molecules that make it possible to see color or to smell or to taste are built on even the smallest variations in organic molecules A few examples of theses are shown below not because you are expected to learned them but more just to say wow this might actually be pretty interesting and make learning organic worthwhi e Hc o OH I H C 0H CH OCH 1 HO c H I 0 NH H OH CHO H C 0H CH0 CHZOH 9 Cinnamadehyde IO Vanillin on 14 Tylenol 8 Glucose c6H1206 OH H r39OH HO j 0 O H n HO HO OH Estrogen Vitamin C brilliant blue food coloring Polymers Now these small organic molecules are amazing given the their complexity and diversity of function but they are not really what is really important about organic molecules Actually it is the ability of small organic molecules to polymerize that makes life really interesting and possible The rest of this lecture describes this process by which small organic molecule units are able to form molecules that have molecular weights of millions and larger We will first look at the polymers built on very simple organic molecules that are responsible for the many products we use in our daily lives like rubber or Plexiglass or Te on We will then look at biopolymers which are as they say the building blocks of life What I will want you to take away from this survey is a general appreciation for how these polymers are formed and for the ones I lay out for you in the notes or the worksheets the ability to identify what monomeric units are responsible for forming a specific polymer Addition Polymers We have learned that there are certain general classes of organic chemical reactions substitutions additions and eliminations You can imagine that these can occur in such a way that a one or more small organic molecules can react to produce molecules of ever increasing size For example the polymerization of ethane to form polyethylene radical addition H H polymerization H2 H JO C p C C C H H H n 2 Fig 1 The polymerisation of ethene in to polyethene Another famous example that is done as a demo just about everywhere including this class is the production of nylon from adipic acid and hexamethylene diamine In the sequence below the two starting materials form the monomer that polymerize to form nylon acid groups 0 o Hod CHz CHZ CHz CHz OH adipic acid amine groups amine group HNiCH2CHzicHzicHzicHzicHziNiH 9 9 1 4 Heh l CHzichCHfCHfCHzichNHC CHfCHzichCHz CHDH H H hexamethylene diamlne acid group polymerization ll ll rillCH2 CH2CH2CH2CH2CH2 IIJ CH2CH2 CH2 CH2 C H H nylon 66 A table of some common monomers their polymer formulas and their famous names is shown in the table below nu 192 Cummon Addillun Polymcn Monomer numc Fomml l nlymcr formula Common name 71m 7 polyulwlm on vlrmundr 39 lcllc39 Vlllyl clllmlde x m nitrilc it 7 H1 Hr rlnm m HH l ltHl pulyprol39lcm m pmpunu HY rlllllhyl murmmlm Cl l 0l39lIl39lCCl I2 I Imglas Lucm Tc nn PTH mtmll unmcrlu nc mmlmg pul mun pill tnm uummlu lmc H l Common sense tells you that the actual commercial production of polymers is not only staggeringly complicated but also staggeringly lucrative So please don t leave this section thinking that heating up a couple of molecules to form a longer chain is all it takes to produce a product or that the simple formulas shown above are the actual structures of the products you buy To achieve certain desirable properties polymers are allowed to form in much more complicated ways as seen in the picture below and in the example of rubber polyisoprene below a Simple polymer Polyisoprene b Alternating copolymer molecule c Block capolymer Disul de link 1 Gran cnpolymev Biopolymers This is not a biology class or even a biochemistry class but unless you have had your head in the sand most of your life you already know that those folks define four basic categories of biopolymers Biopolymers are similar to the polymers described above in that simple building blocks of monomeric units are used to create first important classes of intermediately sized molecules that are then linked to form the biopolymers that define what it means to be alive If you learn nothing else in the material below you should walk away knowing that carboxylic acids combine with hydrocarbon groups to make fatty acids sugars that make polysaccharides that make the carbohydrates starches and cellulose amino acids that make polypeptides that make proteins the bases and phosphates and sugars that make nucleosides and nucleotides that make the nuclei acids DNA and RNA I will brie y define each of these in terms of the simply units that form them and in terms of the important functions they have in our lives What I want you to notice is that even those these are magnificently large systematically defined structures they are at root a collect of bonds formed because an atom wanted to satisfy the octet rule and the reactions that created these polymers were simple acid base or redox reactions based upon the thermodynamic and kinetic concepts that we have been learning Fatty Acids Fatty acids are the simplest of the biopolymers in that they can consist simply of a carboxylic acid functional group with a hydrocarbon chain We can divide these into two categories The saturated hydrocarbons that are made with alkane groups no double bonds These saturated fatty acids are the bad guys that do damage to your cardiovascular system but fast food places love them because they don t go rancid a Butyric butanoic acid CH3CH22COOH w Myristic tetradecanoic acid CH3CH212COOH w Caproic hexanoic acid CH3CH24COOH Palmitic hexadecanoic acid CH3CH214COOH m Cap lic octanoic acid CH3CH25COOH w Stearic octadecanoic acid CH3CH215COOH m m decanoic acid CH3CH28COOH w Arachidic eicosanoic acid CH3CH218COOH w Lauric dodecanoic acid CH3CH210COOH C120 Behenic docosanoic acid CH3CH220COOH C220 The unsaturated hydrocarbons include at least one double bond Myristoleic acid CH3CH23CHCHCH27COOH Cl4l Palmitoleic acid CH3CH25CHCHCH27COOH Cl6l Oleic acid CH3CH27CHCHCH27COOH C18l Linoleic acid CH3CH24CHCHCHzCHCHCHz7COOH C182 Alphalinolenic acid CH3CH2CHCHCH2CHCHCH2CHCHCH27COOH C183 Arachidonic acid CH3CH24CHCHCH2CHCHCHzCHCHCHzCHCHCH23COOH C204 Eicosapentaenoic acid C205 Erucic acid CH3CH27CHCHCH211COOH C22l Docosahexaenoic acid C226 The two essential fatty acids that you must eat to survive C18l Linoleic acid CH3CH24CHCHCH2CHCHCH27COOH C182 Alphalinolenic acid CH3CHzCHCHCHzCHCHCH2CHCHCH27COOH are unsaturated And you can turn on the TV without someone trying to get you to eat as much fish oil as possible because it is the source of omega3fatty acids C204 Eicosapentaenoic acid C205 Erucic acid CH3CH27CHCHCH211COOH C22l Docosahexaenoic acid C226 Carbohydrates Carbohydrates are polymers formed from simple sugars monosaccharides that contain large numbers of hydroxyl groups For example Fructose and glucose are the two monosaccharides with which you are most familiar no doubt because they can combine to form the disaccharide loved by all table sugar sucrose HC o CHZOH I I H c OH HOCIH Ho c H HC H H c OH HCko H c OH CHIOH CHZOH 19 FructoseC5Huo6 18 GlucoseCsH2 6 9 table sugar The chemical reaction that produced table sugar is the formation of a glycosidic bond between the sugars a process that can continue on to form thousands of linkages in what at polysaccarides known as carbohydrates Before you start thinking that carbohydrates are not as important as the two biopolymers we are about to consider the fact is that carbohydrates are the most common living thing of the earth and include I starch which is the way we store energy in the body I cellulose the picture above which is the basic structural unit ofplants Proteins Proteins are a biopolymer formed When peptides bonds are created between amino acids Amino acids as the name implies consist of a simple carbonbased structure that has a carboxylic acid and amine function group note the switch hitting acid and base nature of amino acids along with an organic substituent group The 20 naturally occurring amino acids are listed belowi not the X group is the attached organic substituent mu m Ilu mumllx Uunmlvu mmn Mill lean null x Nwmu WWW x m Alibrmmlum u gm m Hgnlmnr m My mu m H Mn N 11 39leu39 w 7w m m mum m in Mum In H hulnmm m r mun w hmw IIu K mm m n numm nquot lt unmm r x l l mpnmmn39 n mmnu 1 m l i m u k in mm mm m m lm s mquot H in mum m vlmwmr39 Mr V WW I M mun So What can we build with these aminoacids Polypeptides which are small assemblages are one example And a famous representative is hemoglobin which includes four peptides chains surrounding a heme group which is a cyclic organic structure with an iron in it As amino acid sequences form they take on ever increasing layers of multidimensionality shown in the picture below that we like to refer to these as I primary structureithe sequence of linked amino acids I secondary structureiwhich is the three dimensional shape usually a coil helix as shown below or a sheet tertiary structureithe folding that occurs in the larger protein as the sheets and coils come together and try to conform to each other find the lowest energy way of arranging themselves structurally quaternary structureiwhen neighboring peptides or proteins stack together as is seen above when the four peptide units in hemoglobin arrange around each other The impressive array of proteins that are the larger biopolymers formed from these original amino acids units are essential to cell function serving every role imaginable including most famously enzymatic function as we discussed in kinetics lowering the activation energy of a reaction Nucleic Acids DNA and RNA which are the molecule that stores the information that make a living organism unique have to come from somewhere And as the elaborate threedimensional rendering below suggests the building blocks are a but more complicated to unravel than what we have discussed above There are famous stories about how the structure of DNA was discovered and to give you a sense of its importance most everyone knows that Watson and Crick figured out the structure I will describe below but no one knows who figured out cellulose The backbone of DNA and RNA is a sugar called ribose Note the number of hydroxyl groups that define it as a sugar This monomeric compound can form repeating units built on the molecule deoxyribose HOCH2 H 0 H OH HOCHZ H o H on Q Hg y HO OH HO H 20 Ribose C5H1005 239I Deoxyribose C5H1004 Attached to these sugar units are one of four bases you can tell because they have amines on them oh and uuracil substitutes for thymine in RNA 0 NH2 NH2 CH N HN N HN 3 N A N a HZN N H o N o n H 22 Adenine 23 Guanine 24 Cytosine 25 Thymine A base attached to a sugar makes the compound called a nucleoside And When we add a phosphate we form the compound called a nucleotide Base 0 O l O Base 0 CHI 0 D H H H H OH H 27 Anucleoswle 23 Anucleotide Polynucleotides are what you get when you form linkages of nucleotides When nucleotides get large enough they are called nucleic acids And the most famous of these is DNA 0 ll CPPio quot0To o o l CH2 0 Hz 0 o H 0 i ll ll oipio H20 39O P D39 o r Q CH 2 o Cquot 0 f P H0 The great thing about DNA is that it can participate in a chemical reaction that allows for replication which is good for making new people So a sophisticated and in fact ingenious threedimensional structure is needed to allow this to happen Hence the double helical structure that we all know and love And I am through with biomolecules Base pairs Lecture 23 Main Group Chemistry An Introduction We have spent the better part of the school year developing physical models to describe atomic structure chemical bonding and the thermodynamics and kinetics physical and chemical phenomena In all of that however we have been just as content to use generic symbols like A B 9 C D or to describe a weak acid as HA as to actually assign it a real chemical structure with real chemical reactivity Ca Mg Na Remaining elements b Crustal c Human Ca PCIS Others In this chapter we right this wrong working systematically through the main groups of the periodic table leaming for each group and particularly significant elements in those groups I The natural forms in which the elements are found including the hydrides and oxides I The famous chemical reactions that involve the chemical compounds containing those elements I The important practical uses of the compounds containing those elements Common themes in Main Group Chemistry We must have learned something useful during the year that Will help to explain the chemistry of the main group elements Here are some important themes that appear to explain pretty much everything that happens 1 2 L b The number of valence electrons in atoms drive the chemistry of a compound And the main group number corresponds to the number of valence electrons 1BNII 2 13Ill14IIV15IV 16IV17IV Compounds formed by main group elements pretty much always satisfy the octet rule if they can achieving noble gas like electronic configurations There are trends in the periodic table that are pretty much determined by the effective nuclear charge and overall number of electrons in an atom These trends are a atomic radius decreases moving to the right and up the periodic table b ionization energy increases moving to the right and up the periodic table c electronegativity increases to the right and up the periodic table d polarizability increases to the right and down the periodic table e nonmetallic character increases to the right and up the periodic table The second row of the periodic table is very special because overlap of adjacent 2p orbitals creates D bonding and because the significance of intermolecular hydrogen bonding forces In contrast third and higher rows create expanded orbitals to accommodate additional electrons in mushy low energy bonds 5 Pretty much every element except the noble gases forms very stable compounds with itself whether through metallic bonding network solids like C or small covalent molecules like N2 or P4 6 Pretty much every compound forms hydrides reacts with hydrogen Basic ionic hydrides like NaH are found to the left on the periodic table and increasingly covalent acidic hydrides like HCl are found to the right on the periodic table Saline Metallic D Molecular D Uncharacterized or unknown 7 Pretty much every compound forms oxides Basic oxides are found to the left on the periodic table a remarkable array of transitional metal and metalloid oxides with varied oxidation number make up the earth crust and give us the wealth of materials from glass to gemstones that make our lives interesting and end at the right side of the table with the molecular oxides like COZ or 503 that form oxyacids in water If you walked around thinking about these 7 ideas all the time you would have the makings of a pretty good inorganic chemist Hydrogen Belongs to No Group We would like to start with Group I but rst we need to get H out of the way It doesn t really belong to any group given its chameleonlike nature Perhaps the biggest clue for this is that it has an EN of 21 which would position it right smack in the middle of row 2 where it is remarkably adept at picking up a single electron like the halogens to be Noble gaslike and equally adept at losing an electron to form the proton Common forms for elemental hydrogen TABLE 14 Physical Properties of Hydrogen mlmm mlmm mm 5 Nlllml illma u urlui mlmlm gquot Molar mass Abundance Mclling Boiling mushy z Name Symbol lgmol l quotn point Cl poinl Cl lglr39l39 1 hydrogen H IUU8 9993 72w 4 K 72s 10 K 00le l lcumlium 1H Dr D Low 001 71394 9 K 7249 24 K lllx l rlmlm H or 1 mm nullich K 7248 15 K 727 axlme mm mm llw mm ml Appearance in mi clvnlmu m 25 qu l m The dmllv refers m mg mmn mmllnmh There are three isotopes of hydrogen with almost all of it consisting of a single electron surrounding a single proton which means it has a lsl configuration meaning it would be happy both gaining and losing an electron Looking around the universe hydrogen is king with 90 of all the atoms On earth its elemental form is dihydrogen Hz a ammable gas that is so light it just oats off into space On the bright side hydrogen reacts with just about everything to form hydrides 2Ks H2g 9 2KHs or H2 Oz 9 ZHZO like in water or any of the hydride forming reactions in the table TABLE 142 Chemical Properties of Hydrogen Reactant Reaction with hydrogen Group 1 metals M l Ms H1ggt 2 Ml ls Group 2 metals M not B or Mg Ms 4 F145 4 MH7s some drblock metals M 2 Ms R 1413 a i NilUs oxygen Ogl 2 H7g gt 2H701 nitrogen Ng 3 g 1 NHAg halogen X3 X gm Hlg x 2 HXg so there is plenty ofH around if not exactly in the forms we prefer So why to people love hydrogen Because as dihydrogen H2 it produces the most energy per mass of any fuel in the reaction 2H2 Oz 9 H20 474kJ So obviously being able to find or create H2 is lucrative as drilling for oil So what are some ways to make H2 Industrially it is done using a Nickel catalyst to drive the reforming reaction OH HZO 1 C0 3H2 reforming reaction And in the lab you can generate it easily using Zn 2H 9 Zn2 H2 You can even do it in the privacy of your own home by throwing a battery in water But ideally we want to do it with as inexpensive a source of energy as possible and the holy grail of all chemical reactions these days is the photochemical decomposition of water Using sunlight rather than that expensive battery to drive the electrolysis of water hv H20 9 2H2 02 DG 474 kJ Reactions of H2 So what do people do with H2 when they make it 0 Drive cars in the 215t century 0 Extract pure metals like copper from ore M H2 9 Cu 2H when AG is negative 0 React it in the Haber Process to make NH3 which is used to fertilize the earth Group I The Alkali Metals TABLE 143 Group I Elements The Alkali Mcmls anmzrc i39mliglmuiml 715 Nnrmal fm39m son silvergray Iucmis Moiquot mass Melting Boiling Densin z Name Symbol 1g39mulquot point 0 poinl Pct g cnf 3 limium 1 194 IS 1347 053 M sodium Na 98 383 097 l potassium K 4 774 03 1 s7 ubi i Rb 39 68 15 w 5mm a 28 as 187 x7 lraucmm H 17 77 quotNurmul mm Imam he xmu md mpcamncr or rlw ulcmcnl u 15 and 1 arm Alkali metals are a general chemistry student s friend I Has a ls1 electronic configuration I Has a really low ionization energy There is no ambiguity about them Every one of them I Behaves like a metal easily oxidized in donating an electron to form a monocation that are ALWAYS 1 oxidation state no matter the compound I Has really low boiling and melting points and weak bonding I are highly reactive in water and with just about anything I Forms basic hydrides and oxides These materials are the metals stored in glycerin that I trot out every couple of weeks clean up slice to expose a shiny large surface area and then step back to watch explode according to the following displacement reaction 2Na 2H20 9 2Na2 OH39 H2 Note that a base is formed and that the hydrogen gas generated actually catches fire from the heat evolved a b c A similar reaction of the hydride also occurs but Debra doesn t let me do this exciting demo NaH H20 9 NaOH H2 And as proof that the alkali metals react with everything here is Lithium that I don t even get to bring out in the air because it reacts with nitrogen in the air 6 i N2 9 2Li3N No wonder that when you look at the table of half cell reactions right at the top of the table ofreduction potentials are Li e 9 Li 3V Na e 9 Na 2V Which means that the reverse reactions the oxidations are as good as it gets and that these metals are the best reducing agents out there and prime targets for making batteries like say the Li ion battery And finally the ubiquitous nature of the cations Li Na TCr etc means they have found there way into our daily lives in a couple of ways They are the salty taste in your foods They are the colors you see when you start to burn stuff like the yellow in a match ame from the sodium ion They are vital in neurological and metabolic processes in the body in which the relative concentrations of ions like Lilr and TCr and Nair matter But that is biology which I know nothing about Group II Alkali Earths TABLE 144 Group 2 Elements VH Y IL L can Igumzion usl Normal form soft sum 1y metals Molar mass Melting Boiling Density Z Name Symbol gnmr poim C point C 1gcmquot 4 beryllium BC 90l 1285 2470 185 2 magnesium Mg 243l 650 100 174 20 cal um Ca 4008 340 I490 38 sirunrium Sr 8762 770 ISSU 56 barium Bil 13733 7 1640 SS radium Ra 126 700 1300 quotNnmml urm means this state and nppcamncc or hL clcmcm at 1 C and An These metals are quite reactive so you will not find them as metals in their pure form but rather as oxides carbonates or phosphates A particularly famous one of these is the rare gem emerald which is What you get when beryllium oxide is doped with Cr3 ions Emerald Now chemically and unlike the group 1 elements the group H start to show some variety as Be contrasts with the later elements by forming covalent bonds and consequently forming some interesting molecules Beginning with Mg the rest of the elements are metallic Here are some common reactions The metals react in hot water in a displacement reaction with products like the alkali metals Look at the picture of H2 bubbling away when Ca is added to hot water Ca 2H20 9 CaH ZOH39 H2 Alkali metal oxides also are basic and react in water to from hydroxide Ca0 H20 9 Ca ZOH39 Some important applications ofalkali earth chemistry To begin the calcium ion finds itself in a wide array of structural materials like bone and concrete and tooth enamel Why It forms a relatively small doubly charged ion with a lot of charge density and the right size to create powerful material with polyanions like phosphate and carbonate The most common form of calcium is calcium carbonate which is what we call chalk or limestone and is the material on which the city of Austin rests One of the key reaction of limestone is to heat is to form Calcium oxide CaO which is also called quicklime CaC03 9 heat Ca0 CO We have seen just how nasty quickline isiwe added water to it and it boiled so violently that it boiled an egg in CH301 Ca0 H20 9 Ca ZOH39 Now calcium is found notjust in building materials like cements and mortar it is also a building block for structure in the body stuff like bones and teeth So here is something you might not have known How tooth decay works In the first reaction you will notice that tooth enamel Ca5PO43OH is attacked by acid and falls apart Ca5PO43OH 4H 9 5Ca2 3HPO392 H20 But if you could replace the OH39 group in the tooth enamel with something that was about the same size but no where near as reactive with protons like just about anything but hydroxide you might reduce tooth decay So what about uoride which as shown in the reaction below is allowed to replace the hydroxide It is many orders of magnitude less reactive than the hydroxide compound Ca5PO43OH F39 9 Ca5PO43F OH39 But of all the Group H metals the one that has the most important role is Magnesium and it comes in a very unusual way as part of the molecule chlorophyll As shown in the structure below an Mg ion is strategically placed in the middle of a ring structure in the organic part of the molecule One of the responsibilities of the Mg is to keep the ring structure rigid so the energy cascade to form ATP can happen Alternate routes for energy loss like vibrations would prevent the desired energy process from occurring 5 Chlorophyll Group III The B Group The Group III elements are the first to really distinguish nonmetallic and metallic charater in the group Boron With an electronegativity of 20 very much forms covalent bonds And given its odd number of electrons and inability to form four bonds to achieve an octet configuration is involved in forming some remarkable compounds Aluminum is by far the most important of the elements in the row for two reasons it is third only to Si and O in the earth s crust and it is a smallest nonreactive metal Which makes it important in manufacturing Elemental forms of B and Al new ms Snulp nm Lluluunu Wm mlIgumuun quotsinw Mulm nuss Muhng Bmling z Nam Symbol g39mul ll pnim 1c pninl 0 ml 39nrm39 lt Dawn 1 x SI x l Mummmnmumu u Ilummmn u 15 9x mu m 2 7n sllvm nmml 3i gwllmln m 5971 m 24L m 5 i wml w 3 d In 4x lie zuxu 71 silvurwlmrmrml m Ilnllmm 11 1M w m4 m u x7 whimHY m mi 4 m 11 and i There are a variety if allotropes of boron the most famous being Buiall of them are formed in odd ways to achieve an octet configuration Boron is actually extracted from the earth as Na2B4O7 borax The red color of the material is due to an iron contaminant 6 B12 Aluminum is the most abundant compound in elemental form in the earth s crust and the most common element in metallic form although it is not readily mined as a metal Instead aluminum is mined as Bauxite an impure aluminum oxide and turned into alumina A1203 by the Bayer process But the real triumph in manufacturing came when a process was created for producing Aluminum in relatively inexpensive way called the Hall Process Aluminum is removed from the earth as Na3AlF5cryolite melted with Alumina in an electrochemical process with the following overall reaction to produce metallic Al 4A1 60392 3c 9 4A1 3co2 fgf Lde Carbon anode Molten cryolite Molten and alumina aluminum Applications ofB and Al I BOH3 is a Lewis acid boric acid that people love to call the natural or organic way to kill pests Sure I Boron also forms some very interesting compounds with nitrogen called boron nitrides which have the same electronic configuration as graphite and C60 and consequently have prompted a lot of interest in them for new materials 2B 2N39H3 9 ZBN 3H2 Aluminum is used in many manufacturing processes most famously the production of paper Aluminum sulfate is known as papermaker s alum A1203 H2504 9 AlzSO43 3HZO Aluminum oxides are also the basis of many valuable gems When combined With trace metals Sapphire Topal the trace metals added to get the color Cr3 Fe3 and TiM Fe Group IV the Carbon Group You might think that having spent a couple of lectures on organic compounds that we had already covered carbon and the Group IV compounds But actually not even close A look at the elements shows off the remarkable array of elements that form the basis of much of what makes our daily lives more livable ABLE 46 Group HIV Flclucun uli39m39u wniummm billIr Molar nus Mclung Uuiling new z Name Symbol gmulquot pninr quotm puim 5C1 lg39c 1 Nnmul runnv A mrlmn k Izm mm 7 Mick KIunmuIl lgmplvm muhpmm quotmum d1 mm c nunmuml imumm H mm M 1m 1m mm 1 wmmnm m 39 l mu un maulluul m quotn Sn ran mm mle s2 Ind v mu whm mm mcml NurmJlnnu ummmlmu ImIamwJmuu m rlwulmnmu u n ml I m Hu mum lumh m llu 39lnmul ulvhmn For example we have the allotropes of elemental carbon iamon grap ite C50 And we have all the siliconbased compounds which are very likely dominant seeing as how after oxygen it is the most abundant element in the crusta And then we have to deal with the metalloid properties of silicon and germanium that make for a pretty important class of compounds called transistors And who can forget the tin can or that lead has the kind of properties that shield Superman from Kryptonite Carbon Allotropes Of the three allotropes of carbon graphite is the most apparent to us It is what makes up soot activated charcoal and of course pencil lead What is quite interesting about graphite is its structure a series of hexagons with sp2 hybridization This might prompt you to ask what happens with the other p electron in carbon and the answer is that it is part of an elaborate Dbonding structure between sheets of the sbonding C hexagons Among other properties these free oating electrons contribute to electrical conductivity which means oddly enough that Carbon electrodes for electrochemistry are very common a Note also that this is a structure analogous to what is formed with boronnitride compounds as described in the section on Group III compounds Diamond of course is the allotrope of carbon everyone covets For some it is because it is pretty and shiny but engineers like it because it is the hardest compound known and also is the best heat conductor known This means that being able to make it synthetically by subjecting graphite to high pressures and temperatures produces a really great abrasive the best sandpaper known The structure of carbon is actually pretty boringiit is very simply a 3dimensional series of sp3 geometries all sigma bond and so lacking in D bonds doesn t have a lot of electron movement and is an insulator Solid 2 Diamond id 5 3932 n Graphite Gas 2000 4000 9 Temperature K Graphite conducting and spz at high pressure makes diamond insulating and sp3 A final very recently discovered allotrope of carbon is C60 a beautifully symmetrical molecule 39IO BuckminsterfullereneC6 C50 was discovered in the mid 80s and has sent scientists into a frenzy because they have something new to play with Some of the interesting things about C60 are that it is conducting it is a molecule and so can be dissolved in solvents like benzene is a cage that you can put things in like metal that become superconducting at high temperatures it is ofa more general class that includes nanotubes Everyone likes tubes because of all the things you can do with tubes like ow stuff through them The idea that these nanotubes can be used in microelectronics and in nanosensors has the folks over in the nanoscience building very excite Carbon Oxides I would be remiss to not mention the chemical compounds that we have built the city of Austin on Carbonates those compounds formed with the polyanion C03 are ubiquitous They react with cations like the alkali metals and earths to form bones and chalk and as I said the rocks we live on Carbonates also participate in a rich acidbase equilibrium H H HZCO3 9 HCO339 9 CO3 which I have shown off throughout the course for example when I wanted to teach about polyprotic acids and when I wanted to show off the miscibility of gases like CO in water when I had the two love birds from class blow through straws to make a solution of water acidic by commingling it with their shared exhalations of C02 C02 H20 9 H2C03 Silicon Silicon is everywhere because sand and rocks are everywhere And borrowing a page from carbon the Group IV elements are capable of forming an amazing array of very stable chemical compounds I list a few of them here and then talk about them a bit Silicas SiOz like amethyst agate and onyx Silicates SiO4 like asbestos aluminosilicates like mica I won t bore you with learning the names of all the minerals formed from siliconbased compounds but they are legion and vary based upon the level of metal and metal oxide impurities added to them They form the basis for some of our most important synthetic materials including most obviously glasses see mica above and ceramics The manufactured glass we put in our houses is formed by taking sand silica or SiOz and mixing it with varying amounts of metal oxides For example I Sodaline glassimade from melts of SiOz and sodium oxide and calcium oxide I Borosilicates Pyrexiformed from melts of SiOz with B203 Silicones Another very common but very different famous siliconbased compounds are the silicones These guys are not very rocklike because they have been modified with organic materials to create some useful properties The basic form of silicone is a series of repeating SiO units in a backbone iOiSiiOiSiiOiSiiOi to which organic substituents can be added Note that by adding the organic functionality we can make a lot of different interesting compounds The one most known to you is to add alkyl groups to the silicone to make a compound that repels water in windows frames sealants and in waterproofing fabrics Preparing for Groups V VI and VII Before launching into any detail about the rest of the main groups it is important to stop and appreciate that these are the groups with the elements that produce the lion shore of our chemical compounds While it is nice that we have all those rocks and minerals from groups IIV and the transition metals the real work that makes the world go round makes it possible to produce all the manufactured products you use is because of the really nasty collection of reactive chemicals formed from Groups V VI and VII It is unlikely that if you stopped someone on the street and said quick what are the top four chemicals produced in the world that they would say Sulfuric acid phosphoric acid ammonia chlorine But it you want proof at the following table from Chemical and Engineering News and focus on the red highlights PRODUCTION THOUSANDS OF TONS UNLESS OTHERWISE NOTED 1991 1992 1993 1994 1995 19961997 1998 1999 2000 2001a Aluminum sulfateb 1185 1047 1050 1140 1144 1197 1161 1166 1196 1091 Ammoniacn 17169 17924 17195 17869 17403 17923 17891 18475 17337 16806 Ammonium nitratee 7819 7981 8280 8568 8489 8498 8604 9079 7630 7498 Ammonium sulfatef 2243 2391 2432 2584 2647 2662 2702 2787 2599 2868 Chlorineg 11572 11757 12079 12187 12395 12460 12922 12841 13353 13131 Hydrochloric acidh 3301 3610 3492 3754 3904 4116 4570 4659 4499 4718 Hydrogen bcf 100iJ 153 162 213 331 352 386 526 552 454 481 Nitric acid 100k 7927 8136 8254 8714 8840 9205 9433 9285 8945 8479 Nitrogen gas bcf 100n 770 818 796 870 844 816 809 871 858 933 Oxygen bcf 100l 470 515 547 605 630 682 743 676 685 661 Phosphoric acid P205 12109 12826 11515 12792 13134 13210 13159 13891 13708 13143 Sodium chlorate 449 555 539 559 617 662 626 779 818 939 Sodium hydroxide 11713 12244 12466 12539 11408 11563 10973 13113 13199 11518 Sodium sulfatem 794 609 592 652 711 664 706 629 660 509 569 Sulfuric acidn 43466 44524 39839 44813 47519 47770 47929 48512 44756 44032 40054 Titanium dioXideu 1095 1253 1279 1380 1382 1352 1466 1459 1493 1547 1463 Group V Nitrogen Group If you want to ask what would make for the most important compounds they would be the ones that make it possible for us to eat after oxygen which lets us breathe and is still free and does not need to be manufactured So eating requires food and all food comes either from plants and things that eat plants so it would be a good idea to grow a lot of plants But plants need a lot of food themselves in the form of fertilizers so it is not surprising that o ammonia which is the useful form of N that plants love 0 and phosphates which are the useful form of P that plants love are in such high demand So let s concentrate on the first two elements in the group nut 15 I 39l h mup HIV Hemnu Lzll39mi m gummw quot51quot Mulnr Mmng I milmg mm pninl pull 1 Name Smlhol gm cl 3 Nnrmnl 1mm 7 Hum N lHH 72m 4 mw cnlnrluugns H plmsywlmm p r 4 am l 42 wlmr nr rul mmmcml 3 nlsuuc ow 573 gnu lmmllmd 5 mm Sb 5 min 559 Mm m mum mum in bismuth m mwx 271 mu xan wlmrpmk numl m mva mi mum ml mm m m mm a 2m m l m u ukulqu mquot m ulnuvm mum mm H m mum uan Sources ofElemental N and P The source of elemental nitrogen is obviousibreathe It is 75 of the earth s atmosphere P4 is more difficult to come by and requires a high temperature reaction With sand and carbon 2Ca3PO4Z 65i02 10C 9 R 6CaSiO3 lOCO Reactions ofNitrogen and Phosphorous We start With nitrogen Which forms the most stable of all the nonNoble gas compounds With the triplybonded diatomic nitrogen N2 And then one compound later in the group we are looking at phosphorus Which is so reactive it explodes in the air The reason for this different is that nitrogen atom gets to achieve an octet rule like structure by forming secondrow p bonds While phosphorus can t form pbonds and instead contorts itself to make R which has really strained bond angles 3 Phosphorus P4 Now the interesting consequence of these two observations is that the planet is lled with phosphorous found in massive quantities as the rock calcium phosphate and the world is almost completely lacking in nitrogen compounds other N2 which makes up 75 of air Which leads to the two very different ways we produce ammonia and phosphorous Nitrogen xing Elemental nitrogen is everywhere it just isn t in the correct form So we have to fix it And the processes for doing this are I Relying on bolts of lightning to react with the elemental nitrogen I To rely of bacteria that fix nitrogen the organic farmers LOVE this stuff I To produce manufacture ammonia using the Haber process Haber Process 3H2 N2 9 2NH3 Which doesn t look all that exciting exempt that if we are going to make millions of tons of it we are going to want to do it as efficiently as possible Hence the enormous amount of work to optimize the process using just the right catalysts at the lowest temperature possible By the way we know where the nitrogen comes from But what is the industrial source of hydrogen hint look at the beginning of the notes Phosphates We can create phosphoric acid fairly easily from white phosphorous pretty much by sitting back and watching R 502 9 P4010 followed by P4010 9 6HZO 9 4H3P04 Phosphoric acid is used to make fertilizers detergents and adds that zip to your soft drinks But the real source of phosphates used for fertilizers is to simply pull calcium phosphate out of the ground and react it with sulfuric acid and this is the reason we need so much sulfuric acid Ca3PO42 2st04 9 Caso4 CaH2PO42 By the way phosphates are a ubiquitous anionithey are also essential in metabolic processes in compounds like ATP or in nucleic acids a U 7 Adennsine riphaspham mm Enough boring stuff Anything interesting about N or P Well how about this Nitrogen makes some very famous oxides of varying oxidation number 39ABLE I53 rim miiln unl vmcul m Mum idaxmn nYlds unmlm ml Oxomd l39nm mu Hum mi 34 s Np Ni rmmus mi I Nlu m pmwmm m4 A couple of special applications include 0 N20 is nitrous oxide which as I understand it is a delightful way to propel your whipped cream It also is used in the dentist office to make you feel different 0 NO is nitric oxide which as I quote from Wikepedia in a delightfully scientific manner causes the endothelium inner lining of blood vessels to signal the surrounding smooth muscle to relax thus dilating the artery and increase blood ow Whatever that means all I know is that something called Viagra helps to make more NO in the body 0 Nitrogen dioxide N02 is a nasty brown chemical that you can form by tossing a penny into nitric acid It is a major component of air pollution o HNO3 is nitric acid not only one of the strong acids but like sulfuric acid a really fine oxidizing agent It is made in vast quantities commercially using the Ostwald process in an 8electron oxidation process 4NH3 502 9 4N0 6H20 2N0 02 9 2N0 Nitrogen and Bombs Finally these nitrogencontaining compounds find themselves used in the production of explosives And without going into detail let s just say that the reason things like TNT and nitroglycerin work is the same reason that something as simple as ammonium nitrate can be explosive at high temperature NH4NO3S 9 2N2g o2g 4H20g Note that a solid has a Dn of 7 which means that a mole of solid something you can cup in your hand achieves a volume of many hundreds of liters Do it fast enough you have the potential for an explosive Group VI The Oxygen Group This group gets my vote for most underrated After all the real reason we are here very simply is that we are the beneficiaries of an atmosphere which is really reactiveimy goodness 25 of it is the extraoridinaily dangerous compound called oxygen and the only reason we didn t go up in a gigantic ball of ame the first time cavemen discovered fire is the activation barrier to all those combustion reactions we learned are spontaneous in thermodynamics TASK 153 The Group faVI Elcmunh dimp L uI qumliuu min Mulur Melting Boiling Dunsin max onquot point gcnlquotquot z Nam Symbol gmulquot quotcl Cl 15 C x oxygen 0 mm lm its Luv 7 l9 7 l 12 I as u sulfur 5 3205 x 15 445 109 yellow quotunmet olnl 5 34 ulmuum si 73 120 ass 479 gray mmmcmth mud 52 Knimm Tc 2760 m 990 625 ncmllmd 34 pnlunlum m 209 14 960 mu guy memlluld Nnmm Wm mm rho mpcmucc qu mm m m A Icmcm M 1m amt l mu ll ur mi liqml u m 1mm punquot leuuuiu It is also not surprising that the most manufactured chemical compound sulfuric acid is found in this group either Elemental forms of O and S Oxygen in its elemental form has two allotropes diatomic oxygen and triatomic oxygen ozone Oz lfyou are trying to recall where you learned about ozone in this class other than knowing that there is a hole in it the reason is that back when we were learning about the VSEPR model for bonding we trotted ozone out as a 24 electron resonance structure I include its structure here so you can go now I remember 8 Ozone 03 Elemental Sulfur Everyone has a recollection of elemental sulfurit is that yellow powder you always see and has the structure Sg Sulfur is really everywhere but because many of its compound smell we try to stay away from it but for example there are many ores that contain sulfur The third in collection of rocks containing S is called pyrite or Fool s Gold which nerd kids like me thought was pretty cool Sulfur is also an undesirable component of petroleum and natural gas where it is found as HZS As a result it is not hard to produce the elemental form especially given its relatively low melting point The process used to claim it from petroleum is the Claus process in which the His is first oxidized to 502 HZS 302 9 SO ZHZO HZS SO 9 35 ZHZO Reactions of Oxygen containing compounds 02 Of course the reactions of oxygen are the reactions that drive everything toward a higher oxidation state from the combustion reactions I do in here daily to keep you awake o the metabolic processes in biology that are utterly fascinating to prehealth professions students I won t spend any time on these reactions since they are rammed down your throat your entire life as a scientist but I will say that end the end everything rusts everything get a much of Os attached Stop ghting the inevitable Sulfuric acid It is not surprising that I will spend some time talking about how to make the most important molecule this side of 02 and how to use it The production of sulfuric acid is a multi step effort that believe me has been perfectly I list a grossly simplified form of it here so you can see how that S that we extract from petroleum gets turned into sulfuric acid S 02 9 302 athOOOC 2802 02 9 atSOO OCvvithavanadiumcatalyst SO3 H20 9 H2804 And what would be do with this sulfuric acid It happens to be great at three things 0 It is a strong acid 0 It is a strong oxidizing agent 0 It is a great dehydrating agent it removes water We have already seen it in action twice now Once to extract metals from the earth And more recently and most importantly like 60 of its use to create useful phosphates Ca3PO42 ZHQSO4 9 CaSO4 CaH2PO42 It is also used in the paper making process to make aluminum sulfate A1203 3 H2804 gt A12SO43 3 H20 Of course it finds its way into lead acid batteries where it is part of a famous battery And of course it is a staple of every chemistry circus creating carbon out of sugar in a dehydrating reaction ciszzoii 9 12C lleO Group VII The Halogens TABLE ISA Ilvc Lump I lvll lzlemcnls l ulrm K WW Mum Mn lllng mung Dmmly may point mini gmr w Z Name bymlml lgmul H Cl 2 m JVC Normal funn v Huurmc muu 7110 7 138 LS r mum rnlnrkss ms l7 LMIH III l 1139 W e Hquot 7 H kmquot yulhm g 3a I m u 7900 7 w 31 Cd Imd 39 LG 0 H4 w 49 t mmnwmllenlul m x5 nmrmu m mm mm u m m m m clmmm M 5 and x Mm The halogens get a lot of publicity because they have a cool name did you know the name for group VI is the chalcogens See Group VI needs to hirer a better PR firm Halogens are especially useful to the chemistry educator because they sit at the extreme end of the periodic table and serve excluding the Noble gases as the Compounds that are the smallest atoms and ions Compounds with the largest electronegativities I Compounds with the largest ionization energies Their elemental form is a very reactive oxidizing agent I The compounds thatjust have to add a single electron to be happy The second thing you think of when you make a salt Elemental forms of halogen Like the alkali metals there is a remarkable sameness to the halogens They are all reactive diatomic gases Also of interest just as the second row Li has a souped up ability to react compared to the other alkali metals F2 has a souped up ability to react as well because of its very high electron affinity and small size Oh and time out for a deep though on why the oceans are filled with NaCl and f is no where to be found in the water F is actually quite abundant in minerals on the planetifor example it is the mainstay in the mineral cryolite Na3AlF6 we pull out of the ground to make metallic Al And yet NaCl gets all the name recognition Which can be traced to our friend charge density Because F is so small and the charge density larger in the rocks and minerals it forms it is less able to dissolve in water compared to the Cl39 ion Despite all the excitement surrounding uorine and all the cool reactions it can do like being the first compound people reach for when they want to make a really difficult reaction happen for example see the reactions of Noble gases in the end most F used in manufacturing in the world ends up in the molecule UF6 which is used to process nuclear fuels Chlorine As you might have noticed from the table of industrial compounds manufactured in this country C12 battles next and next for the fourth position The source of C12 is the electrolysis reaction of NaCl NaClmolten 9 Na 1 C12 You may recall that on the last day of electrochemistry I pretended to melt some NaCl and toss a battery into it Well if I had done it I would have contributed to the way C12 is manufactured Something tells me though they do it a little more safely thanl was about to try Once you have C12 what can you do with it Just about anything C12 is a very fine oxidizing agent that reacts with just about everything but C N2 and 02 The compounds it forms are everything from bleaches to water purifiers to disinfectants to dry cleaning agents to pesticides C12 is also readily converted into HCl and oxyacids C12 H20 9 HCLO HCl Which have many uses Group VIII The Noble Gases Every chemistry course begins by pointing that chemical reactions occur primarily to allow atoms to achieve electronic configurations that look like Noble gases By that we mean having an nsznpg configuration which the exception of nl This is the source of the less sophisticated notion of satisfying the octet rule and the more sophisticated notion of achieving stable filled shells that are energetically favored The length to which compounds go to end up like this is remarkable and for example that is how we end up with a compound like elemental phosphorous P4 which has a Noble gas configuration but to do so has such strained bond angles that it is literally explosive in air Well you can imagine that once you achieve your goal of becoming electronically stable you don t really feel like doing anything else and that can certainly be said for the Noble gases shown below TABLE 156 The Group ISVIII Elamnu the Noble Cases VdL39IIL39L mungumzmm 1151117 Nm39mu form colorlcss molmmmk m Molar mass Melting point Boiling point Z Name Syman g mol W c1 2 2 helium He 400 7 29 42 K 10 neon NC 10124 7249 1 IS argon r 3995 718 7186 35 kl39ypmn Kr mm 7 I 7 715 54 xi39nun Xe IS I 9 r I ll 7 ms 86 I39dun39 Rn 212 771 752 minimum They are in fact so okay being themselves that they aren t even interested in appreciable intermolecular interaction and as a consequence are gases at room temperature We have to cool things way down to make liquid helium or neon or argon as you see a ove Of course being a really stable unreactive really cold material has a lot of really valuable uses and that is why you see trucks of liquid Noble gases ying down the interstate all the time As for reactivity even though the gases have a very high ionization energy they can only stand so much electrocution before the electrons are excited to higher energy level and even ionized And as the excited gases relax back to the ground state they emit characteristic light that makes for exciting 639h Street and Bourbon Street images These are of course being replaced by 400 foot by 1000 foot LED displays of the latest Target ad campaign as my recent trip to New York has confirmed so look at the pretty picture below if there aren t any left in the real world Chemical reactivity As mentioned Noble gases don t react which is exactly the kind of absolute statement that drives scientists to the lab to prove they can do it And for years desire to be the first to make a molecule with a covalent Noble gas bond was something to do The first success was not surprisingly the consequence of taking a large polarizable Noble gas like Xe with the most reactive stuff out there F2 to make the compound XeF4 at high temperature and pressure Lots of other compounds with Xe have been made since then like the acid below 39I8 Xenic acid H2Xe04 And for those ofyou thinking that maybe you would like to be the first to make some compounds with Kr that has happened with the formation of not surprisingly KFZ And that is all I have to say about main group chemistry Lecture 16 Electrochemistry The Big Picture Electrochemistry follows the adventures of the electron electron 6 Recall that we first discussed the electron when it came up as a fundamental particle back when discussing quantum mechanics Also recall that when learning about configurations for atoms and molecules that we obsessed over it But as we went on to discuss thermodynamics and properties of the bulk we put it away It is back now demanding its own chapter and perhaps its own consideration in thermodynamic terms After all we spent six weeks on the fundamental particle called the proton and it has nothing on the electron from a reactivity perspective How do we know this Think about it from a charge density perspective as we compare some particles of different charge and size Type of particle e39 H H Na mass per particle 83 X 103927 g 16 X 103924 g 16 X10quot24 g 37 X 103923 g mass per mole 12000 gmole l gmole l gmole 23 gmole charge per particle 1614x103919 C 1614 x 1039 C 0 1614 x 1039 C charge per mole 96 x104 Cmole 1F 96 x104 Cmole 1F 0 96 x104 Cmole 1F Note that while the mass of an electron is quite small 2000 times smaller than a proton and 50000 times smaller than a sodium ion It has the same amount of charge which means that its charge density is vastly larger than any other particle Seeing as how we have on many occasions we have used charge density to rank reactivity having stumbled across a particle with 2000 times the charge density of the neXt guy in line we should be willing to examine it more carefully Time out for charge Everyone understands mass you step on scales every day to see how much you weigh and are used to buying goods by the pound or gram And that is why we can talk about the mass of a mole of an atom and you just look at the periodic table and rattle off uranium weighs 238 gramsmole But charge is not so familiar You are used to the notion of charge in the form of static electricity or getting a shock but have no real quantitative feel for it Until now Very simply 0 The unit for charge is the Coulomb in the same way the unit of mass is grams and 0 In the same way you can assign a mass to a mole of a compound like water is 18 gramsmole you can assign a mole of charge to something And the best part is that a mole of charge always has exactly the same value 1 mole of charge l Faraday 96 x104 Cmole And this value is the same whether you have a mole of e39 or a mole of H or a mole of Na The chemistry of the electron oxidationreduction reactions We have just finished a unit on equilibria in which we looked at reactions in which we followed the movement of a proton and reactions in which we followed the movement of cations and anions Acid base reactions solubility reactions H 6 proton Na or Cl39 cations or anions NH3 HNO3 2 NH4 N032 NaCl AgNO3 2 NaNO3 AgCl Note that in both cases the oxidation number does not change for example in the acid base reaction oxidation numbers of H 1 N 3 and O 2 are assigned for every atom on both sides of the reaction In contrast in electrochemistry we focus on reactions in which the formal oxidation number assigned to an atoms in a reaction changes In every oxidation reduction reaction at least one atom is oxidized increases in oxidation number while at least one atom is reduced decreases in oxidation number For example 0 1 2 1 2 1 0 6 note the Na atom oxidation number increases while the H atom oxidation number decreases Na H 20 2 Na OH39 H2 0 0 1 2 6 note the H atom oxidation number increases while the O atom oxidation number decreases 2H2 02 What we do in electrochemistry is follow the flow of electrons along this chemical reaction path Time out if you can t assign oxidation numbers as easily as you breathe you Will fail the electrochemistry material So here is a refresher brought to you by your friendly neighborhood chemistry professor Assigning oxidation numbers What do oxidation numbers tell us Very simply oxidation numbers tell us where the electron density is in a compound kind of like all that work we did with quantum mechanics at the beginning of 301 but with none of the huge equations and complicated rules So in the ion dichromate 6 2 CI392O72 the electrons are more densely packed around the 0 though than Cr and you can tell this because the more negative the oxidation number the greater the electron density Note surprisingly this result is consistent with everything you learned about oxygen loving electrons and metals not wanting them So what are the rules for oxidation number rather than try to memorize all the possible combinations learn the following hierarchy of rules Rule 0 Free elements have an oxidation number of 0 Example Oxygen in 02 has 0 oxidation number Rule 1 Assigning oxidation numbers to the groups from the left the common formal charge on an element increases 1 2 3 From the right skipping the noble gases the common formal charge on an element increases 1 2 3 So alkali metals are 1 Halogens are 1 etc Complications involving hydrides H and oxides O with other elements in compounds Rule 2 Alkali metals are always 1 except for rule 0 Example Na in NaO is 1 Rule 3 Hydrogen is always 1 except for rules 0 and 2 Example H is 1 in NaH but 1 in H20 Rule 4 O is always 2 except for rules 0 2 and 3 Example 0 is 05 in NaOZ but 2 in H20 Rule 5 In every redox problem you do assign the oxidation numbers in order using rules 0 4 There will usually only be one element left to assign by difference Example what is the oxidation number of P in K2HPO4 Example of setting up problems to determine oxidation numbers for unknowns What is the oxidation number for P in KZHPO4 charge on the molecule 0 0x of K of K atoms 0x of H of H atoms 0x of P of P atoms 0x of O of O atoms Using rules 0 4 above we can assume K is 1 H is 1 and O is 2 so sticking these values and the number of atoms in the equation above charge on the molecule 0 12 11 1 24 so 0x P 5 You can set up this kind of equation while you are still learning oxidation numbers but by the exam this should be something you do in your head pretty easily An Introduction to Oxidation Reduction Reactions and How to Balance Them Most of the cool demonstrations I show in class are redox reactions This is either because there is a lot of energy associated with the reaction remember the charge density of an electron or because different oxidation states of metals have very different colors Here are some of my favorites from class Examples 1Dr Laude pours hydrogen peroxide in his ear to get rid of ear wax is a redox reaction 1 1 1 2 0 2H 202 x 02 Note that the O in H 202 is oxidized in 02 and the O in H 202 is also reduced in H20 2 Transition metals exhibit neat color changes and are redox reactions 7 6 4 2 6 oxidation number of Mn MnO439 9 MnO4 9 MnOZ 9 Mn2 6 chemical species of Mn purple green brown sohd clear 6 color Of Mn 3 Exploding H2 balloons occur almost daily in class and are redox reactions 0 1 2 2H 2 02 2H20 H in H 2 is oxidized by 1 e and O in 02 is reduced by 2 e 4 Burning gummy bears and all combustion reactions are redox reactions 0 1 2 0 4 2 1 2 C6 H12 06 602 x C in C6 H12 06 is oxidized by 4 e and O in 02 is reduced by 2 e 5 Displacement reactions in which I toss sodium metal in water and head for cover are redox reactions 0 1 2 1 0 21 2Na 2H20 2Na H2 20H Na is oxidized by 1 e and H in H20 is reduced by 1 e How to balance chemical reactions yourself the quick and dirty and best way to do it Did you notice that those chemical reactions above were all balanced By thatl mean that the number of atoms and the amount of charge was the same on both sides of the chemical equation and one would expect if mass and charge are to be conserved So how do you balance a reaction Often it is by inspection with simple acid base and solubility reactions a little common sense is all you need Redox reactions are a different beast They are hard to balance because really substantial changes in the oxidation number occurring in two paired half reactions can make for some large coefficients And if the reaction is happening in an acid or base solution the problem is further complicated So I am going to show you a nice step by step method often called the change of oxidation number It is to be preferred over the hideously complicated half reaction method that takes forever and requires a lot of redundant work But hey use a method that is long and complicated I don t really care though your exam grade might The change in oxidation number method 1 Assign oxidation numbers to each atom in the reaction J Determine the number of e s for each reduction and oxidation half reaction U3 Determine the least common multiples for the two half reactions and use these numbers to balance the reaction coefficients at this point the number of electrons oxidized and reduced should be equal in the reaction 4 If in acid add one H20 to the opposite side for each deficient 0 Add 2H to the excess 0 side for each added H20 U If in base add 2 OHquot to the opposite side for each deficient 0 Add one H20 to the excess 0 side for every 2 OHquot added Example 1 balancing with no acid or base FeClz SnCl4 2 SnClz FeCl3 unbalanced reaction 2 1 4 1 2 1 3 1 FeCI2 SHC14 SIlCl2 FeC13 step 1 assign oxidation numbers 2 1 4 1 2 1 3 1 FeC12 SnCl4 2 S pClz FeCl3 I 2x le T step 2 determine the electrons per atom oxidized or reduced in green 1X26 2FeC12 1nC12 2 1nC12 2FeCl3 step 3 the least common multiples l and 2 are placed as coef cients in the reaction in red The reaction is now balanced You can check by noting that the number of atoms on each side is the same and the overall charge on each side is 0 Example 2 balancing redox reactions in acid 2 2 3 MHO4 F6 MH Fe unbalanced reaction 7 2 2 2 3 2 2 3 MHO439 Fe MH Fe step 1 assign oxidation numbers le x 5 2 2 3 MnO4 Fe F Mn Fe step 2 determine the electrons per atom oxidized or reduced in green I 56 X1 1MnO4 5Fe2 1Mn2 513 step 3 the least common multiples 5 and l are placed as coef cients in the reaction in red MnO4 5Fe2 Mn2 5Fe3 20 step 4 add4 waters to side de cient in O and 8H MnO4 5Fe2 x Mn2 5Fe3 20 and add 8H to opposrte s1de The reaction is balanced You can check by noting that the number of atoms on each side is the same and the overall charge on each side is 17 Example 3 balancing redox reactions in base 2 3 Fe MHO439 MHOZ Fe unbalancedreactiou 2 7 2 4 2 3 2 3 Fe MnO4 MHOZ Fe step 1 assign oxidation numbers 3e X 1 2 3 Fe MnO4 F Mn02 Fe step 2 determine the electrons per atom oxidized or reduced in green I le X 3 T 31362 1MnO439 1Mn02 3Fe3 step 3 the least common multiples 3 and l are placed as coef cients in the reaction in red 3Fe2 MnO4 MnO2 3Fe3 step 4 add4 hydroxrdes to Side de crent in O and 2H 0 3Fe2 MnO 39 x MnO 3Fe3 add 2 waters to opposite side 2 4 2 The reaction is balanced You can check by noting that the number of atoms on each side is the same and the overall charge on each side is 5 The important place you nd these redox reactions batteries As we nish up redox reactions note that the ones we are interested in are those that make useful things like batteries In fact a battery is simply a couple of redox half reactions that can be put together so that E is positive and some work can be done So as you consider the electrochemical cell conventions below understand that they are useful in helping to describe the following kinds of famous batteries Famous modern batteries use a variety of chemicals to power their reactions Typical battery chemistries include Zinc carbon battery Also known as a standard carbon battery Zinc carbon chemistry is used in all inexpensive AA C and D dry cell batteries The electrodes are zinc and carbon with an acidic paste between them that serves as the electrolyte Alkaline battery Used in common Duracell and Energizer batteries The electrodes are zinc and manganese oxide with an alkaline electrolyte Lithium photo battery Lithium lithium iodide and lead iodide used in cameras because of its ability to supply power surges Lead acid battery Used in automobiles The electrodes are made of lead and lead oxide with a strong acidic electrolyte Rechargeable Nickel cadmium battery Uses nickel hydroxide and cadmium electrodes with potassium hydroxide as the electrolyte Rechargeable Nickel metal hydride battery Rapidly replacing nickel cadmium because it does not suffer from memory effect Rechargeable Lithium ion battery Very good power to weight ratio often found in high end laptop computers and cell phones Rechargeable Zinc air battery Lightweight rechargeable Zinc mercury oxide battery Often used in hearing aid batteries Silver zinc battery Used in aeronautical applications because the power to weight ratio is good Metal Chloride battery Used in electric vehicles We will have a separate lecture on famous batteries to end our presentation on electrochemistry but for now sit back and offer your thanks to the chemists and engineers who have made your life a walk in the park with a dozen batteries on your person Electrochemical cell convention Regardless of how we draw the picture of an electrochemical cell As a battery As a couple of isolated beakers Carbon rod cathode Zinc cup anode MnOz carbon black NH4C electrolyte As cell notation AgIAg 01MI Fe3 01MIFe2 1MPt Or as a chemical reaction 8HMnO4 5Fe2 Mn2 5Fe3 4H20 Electrochemical cells consist of the same simple parts a couple of half reactions and a way to isolate the systems to allow current to flow across a voltage drop When you think about it the only difference between the hydrogen balloon that I explode in class and the hydrogen car of the future is that someone has done a good job of packaging the reaction so that you can control the work done the electrons that move by how much you put your pedal to the metal So what are the conventions used in describing the parts of an electrochemical cell For this course you will need to be able to distinguish 0 The magnitude and sign of the electrochemical cell potential in other words whether the cell has E or E Where oxidation and reduction occur Electrode name cathode and anode Electrode sign and Electron flow direction To begin assigning cell convention and to perform any kind of electrochemical cell calculation you have to know whether you have a cell that is spontaneous or a cell that is non spontaneous this brings back memories of thermo which is quite appropriate as we will see shortly If an electrochemical cell is spontaneous we can say the following about it and mean the same thing E for a spontaneous reaction and A G is and K gt 1 These cells are called battery voltaic galvanic If an electrochemical cell is non spontaneous we can say the following about it and mean the same thing E for a non spontaneous reaction so A G is and K lt 1 These cells are called electrolytic or electrolysis cells All cells do share common features 0 Two 12 cells are involved one oxidation and one reduction 0 Electron flow through the external wire to the cathode in both cells 0 Oxidation is at the anode and reduction is at cathode in both cells The only distinction between the two kinds of cells is the sign convention 0 In battery a cathode anode 0 In electrolysis cathode anode When I am in WalMart I always remember that the on the batteryI see is the cathode and everything follows from that So let s put these ideas for cell convention in a table and memorize it for some easy points on tests electrochemical reaction type AG E reduction oxidation direction of e ow sign at sign at cell type cathode anode electrolysis non spontaneous cathode anode e flow to cathode galvanic spontaneous cathode anode e flow to cathode battery Example Identifying Cell Conventions So let s apply this set of conventions to the nice copper zinc battery below Create a list of all the things you can say about this picture Salt bridge Electrons VoltmEter Electrons N lons Ions I Anode 2 Oxidation Reduction Zns a Zn2aq 2 e Cu2aq 2 e a Cus Things you can say about the picture of the cell 0 It is a battery because E is positive which means the reaction is spontaneous The zinc is oxidized at the anode which is written as the leftmost electrode The copper is plated onto the cathodic electrode The Sign of the anode is and the sign of the cathode is The electrons are owing through the external circuit to the cathode A salt bridge is being used to complete the circuit The potential difference is a large one 11V which suggests this might be a good battery if only we could get the voltage up to 15V wait till next lecture A brief aside Electrochemical Shorthand for lazy people like your professor and all other chemists No one likes to draw cells So they use electrochemical shorthand and substitute the following symbols and convention to represent the pretty beakers 6saltbridge 6 phase change CuICu2 6 Half Cell Also by convention the anode is always written first on the left side Put all this together and written succinctly below is a zinc copper battery ZnIZn2 Cu2Cu 6 shorthand for battery we just drew We can even add concentrations AgIAg01MII Fe3 01MFe2 1MPt Is a battery in which oxidation takes place at the silver electrode reduction take place on a piece of platinum wire for Fe and the starting concentrations are as written Let s get Quantitative with Electrochemistry Electrochemistry is just another way of describing thermodynamics The kinds of things we found useful in thermodynamics like understanding whether a reaction happens or the extent of the reaction can be determined with electrochemistry Proof of this statement comes from comparing the simple relationship between K from equilibria AG from thermodynamics and now E for electrochemistry in the equations below RTan A G nFE Note that the units of each equation are a measure of energy change in a chemical reaction It is kind of neat to see all the ways that we have defined energy this spring gases gases work heat electrochemistry PAV AnRT w AH q units of I units of I units of I units of I units of I and realize that it is just the way we account for the energy change that is different 0 In thermodynamics we keep track of energy as measured in Joules 0 In equilibria we keep track of the ratio of concentrations 0 In electrochemistry we keep track of the electrochemical potential for a population of electrons The three graphs below provide another way to View the similarity between K AG and E e e e e e Qamount of change EJ EV AG V Deep though number 1 on Why you should love electrochemistry Note that these simple relationships allow us to convert from thermodynamics in one form to another For example if you have a value of AG from a table of thermodynamic constants you can calculate K Or if you have a voltmeter that measures V from a cell reaction you can obtain AG values to put in a table And unlike thermo or equilibria for which you have to use complicated devices like spectrometers or bomb calorimeters to find values of K or AG all you need to nd electrochemical potentials EV is a voltmeter you can buy at Radio Shack for 10 A comment on the electrochemistry plot above and why it is SO profoundly important conceptually Everyone gets energy and how it describes extent of reaction Everyone gets concentration and how it describes extent of reaction Few intuitively get electrochemistry qE and why it describes the extent of reaction SO spend some time looking at this plot below and appreciate that it is the combination of the amount of electrons and the potential hill they fall down that define work Think of it this way some people say that it is the current that kills and others say that it is the voltage that kills Actually it is both The amount of e determines the current per unit time and must obviously be larger to give someone a shock At the same time the size of the hill that must be traveled down matters as well Hence the work that is done in a chemical system is equal to the produce of q and E This is the number of charges as per unit time the current i For electrochemistry to do much work the size of the hill V and the amount of charge q both need to be large Oh this must mean work w qV this is the voltage V difference measured by a voltmeter D EV Calculating Cell Potential Table of Standard Reduction Potentials and the Standard Hydrogen Electrode You have begun to see examples of half cell reactions being put together to make cell potentials Above we saw a cell potential of 11V for zinc and copper Could be create a table of all the possible electrochemical cells Sure but we would have millions and millions of cell reactions Is there a simpler way to do this What about using a standard to which all half cell reactions are compared For example just for kicks let s choose a cell reaction like 2H 2e 9 H2 and decide to give it a reference voltage of 0V Let s even call it a Standard Hydrogen Electrode SHE We can even choose a set of standard conditions like a standard temperature 298K and concentrations 1M or 1atm Now let s remember from thermodynamics that Hess said we didn t have to care about the path that a reaction took it was only how things started and ended that mattered This means that if every half cell is referenced to the standard hydrogen electrode we can put them in a single table and directly compare them to each other after substracting out the SHE potential which is 0V what a good idea for a voltage to subtract Presented below is the Standard Reduction Potential Table Note that by convention all the half reactions are written as reductions Also note that all are compared to the SHE and there is a voltage range of from 3V to 3V We can decide to put these half cells together then to find the voltages for a cell potential The equation we will use is Ece11 Ecathode39 Eanode 0T Ece11 Ereduction onidation Example What is the standard cell potential for a battery formed by the following half reactions Au e 9 Au Na e 9 Na Note that the half reactions are 169V and 271V respectively And if we put them together to form a battery a positive E value then the Au half reaction must be the cathode and the sodium half reaction the anode E0311 Emmod Emde 169 271 44V which is a pretty hefty battery TABLE 12 Standard Potentials at 25 Cquotquot Species Reduction halfreaction E V Oxidized form is strongly oxidizing FZF F2g 2 e a 2 Fwaq 287 AuAu Auaq e gt Aus 169 Ce4Ce3 Ce4aq e gt Ce3aq 161 Mno4 HMn2HZO MnO4 aq 8 Haq 5 e gt Mn2aq 4 H200 151 CIZCl C12g 2 e gt 2 Cl aq 136 Cr2072 HCr3HZO 1207 14 Haq 6 e gt 2 Cr3aq 7 H200 133 02 HUHZO 02g 4 Haq 4 e gt 2 H200 123 082 at pH 7 BrZBr Br2l 2 e a 2 Br aq 109 NO339HNOHZO NO3 aq 4 Haq 3 e a NOg 2 H200 096 AgAg Agaq e gt Ags 080 le3Fe2 Fe3aq e gt Fe2aq 077 121 12s 2 e a 21 aq 054 OPHZOOH 02g 2 H200 4 e gt 4 OH aq 040 082 at pH 7 Cu2Cu Cu2aq 2 e gt Cus 034 AgClAgCl AgCls e gt Ags Cl aq 022 HH2 2 Haq 2 e gt H2g 0 by definition Fe3Fe Fe3aq 3 e H Fes 004 OZHZOHOZ OH 02g H200 2 e Hogaq OH aq 008 Pb2le Pb2aq 2 e gt Pbs 4013 Sn2Sn Sn2aq 2 e gt Sns 014 Fe2Fe Fe2aq 2 e gt Fes 044 Zn2Zn Zn2aq 2 e7 gt Zns 076 HZOHZOH 2 H200 2 e a H2g 2 OHaq 083 042 at pH 7 A13A1 A13aq 3 e a Als 166 Mg2Mg Mg2aq 2 e gt Mgs 236 NaVNa Naaq e gt Nas 271 KK 1ltaq e gt Ks 293 LiLi Liaq e gt Lis 305 Reduced form is strongly reducing quot For a more extensive table see Appendix 2B A final deep thought to tie Electrochemistry to Equilibria Strong oxidizing and reducing agents Electrochemistry is thermodynamics and equilibria is thermodynamics so I bet the ideas we develop for electrochemistry look like the ideas for acid and bases For example remember how we ranked acid and base strength from the K3 and Kb Also remember the simple relationship between Ka and Kb using Kw Acid strength increased as Ka increased Basic strength increased when Kb increased So in the chart below HSO4 is the strongest acid and NH4 is the weakest acid NH3 is the strongest base and 04 is the weakest base AcidBase Strength Ka Dissociation reactio Kb Strongest acid 9 10 2 H804quot H 804 72 10 12 105 HCOOH H COOH 109 Weakest acid 9 109 10 5 NH4 H NH3 6 Weakest base Str0ngest base OxidationReduction Strength We can create similar rankings of oxidation and reduction strength using the half cell reactions The question now is what is most easily reduced or what is most easily oxidized The answer The easiest is always the most positive value in the same way that acids and bases are strongest dissociate easiest with the largest K values Note other similarities in the table below There is an on value that is related to End in this case by an opposite sign Also note that the Box reaction is for the reverse reaction that is not actually written In this table the strong reactants are the most positive ones Cu is the strongest oxidizing agent because it is most easily reduced Zn is the strongest reducing agent because it is most easily oxidized End 12 Reaction reduction on Weakest oxidizing agent 9 7 7 6 Strongest reducing agent hardest to reduce 39 Z 2639 2 Z 39 easiest to oxidize 0 2H 2e 2 H2 0 Strongest oxidizing agent 9 6 Weakest reducing agent easiest to reduce 3 Cu 26 2 Cu 3 hardest to ox1d1ze Example What are the strongest and weakest oxidizing and reducing agents in the large table of reduction potentials Answer Just as with the smaller table above look to the diagonal corners The most positive value is the strongest oxidizing agent F2 The most positive reducing agent most easy to oxidize is for the most negative reaction and its reverse reaction that is not written Li Just to be clear about Free Energy GHTS straight line assumes that H and S are independent of temperature G Solid TltTm 39 Solid has Slope is given by S Liquid has a larger entropy and therefore a steeper slope Liquid T gt Tm Liquid has the lower free the lower free energy Principles of Chemi stry energy Vandxen Bout Super Cooled or Super Heated Kinetically trapped in nonequilibrium state quotSupercooledquot trapped in liquid state due to slow crystal formation quotSuperheatedquot trapped in liquid state due to slow bubble formation Demo Principles of Chemistry II Vandxen Bout Last Phase change What is a key difference between evaporation and boiling A liquids only boil at atm total pressure B liquids only evaporate at room temperature C bubble form in liquids when boiling D nothing Solutions Solutions are homogeneous mixtures of multiple compounds Solution Major component Solvent language typically used for liquids salt water air Minor component Solute steel Principles of Chemistry II Vandxen Bout Let39sooltatthefoowingquotreactionquot Let39sooltatthefoowingquotreactionquot Let39sooltatthefoowingquotreactionquot I39I O 0 What has to happen Lose solventsolvent interactions IMF Lose solutesolute interactions IMF Gain solutesolvent interactions Enthalpy of Solvation AHsoivation hard to predict AHsolvation 0 Ideal solution Solutesolvent interactions are identical to solutesolute and solventsolvent AHsolvation gt 0 Typical Solutesolvent interactions are weaker than solutesolute and solventsolvent AHsolvation lt 0 Unusual but possible Solutesolvent interactions are stronger than solutesolute and solventsolvent Principles Of Chemistry II Vanden Bout Entropy of Solvation Assolvmon easy to predict Solutions have a higher entropy than the unmixed compounds Therefore Assolvation gt 0 Principles of Chemistry II Vandxen out TABLE 172 Values of A520n for Several Salts Dissolving in Water AS Process J K 1 mol1 KCls gt Kaq Claq 75 LiFs gt Liaq F aq 36 CaSs gt Ca2aq 52 aq 138 Gibb39s Free Energy of Solvation AGsolvation If AGsolvation lt 0 solution strongly favored If AGsolvation gt O undissolved state is strongly favored AGsolvation AHsolvation 39 T Assolvation Best case AHsoIvation lt 0 Generally the best you can hope for is AHsolvation O What makes an ideal solution Same IMF for solutesolvent and solutesolute and solventsolvent quotlike dissolves likequot Polar compounds dissolve polar compounds ionic Nonpolar compound dissolve nonpolar compounds Principles of Chemistry Ill Vandxen am Which is most likely to dissolve best in water A methanol CH30H lt B butanol C4H9OH C octanol CanOH D didodecanol C2H250H Which is most liker to dissolve best in hexane C6HI4 A methanol CH30H B butanol C4H9OH C octanol CsH 7OH D didodecanol C2H250H 4 Temperature Dependence Generally atT goes up solubility increases 300 Sugar C 2H2201 1 260 KNo3 220 180 140 100 Solubility g solute100 g H30 60 N32504 KC 20 39260413 I 0 20 4O 60 80 Temperature C 100 Principles of Chemistry II Vanden Bout Gas Dissolved in 21 Liquid Henry39s Law TABLE 173 The Values of Henry s Psolute Ksolventxsolute Law Constants for Several Gases Dissolved in Water at 298 K T Gas 12H ltarmgt mole fraction CH4 413 gtlt 102 C02 164 gtlt 103 02 434 gtlt 104 CO 571 x 104 H2 703 x 104 N2 857 gtlt 104 Principles of Chemistry ill Vanden out In General Henry39s Law constants increase with increasing Temperature Less gas is dissolved at higher temperatures Principles of Chemistry II Vandxen Bout Pressure arm Phase Diagram of C02 Temperature C gt Phase Diagram of Water Critical point PL 2 I 8 Liquid Pressure mm 0 T3 100 374 00098 Temperature C Figure Copyright Houghton Mifflin Company All rights reserved At a constant temperature increasing the pressure will cause ice to melt it moves to the higher density phase which for water is a liquid Principles of Chemistry II C Vanden Bout Phase Diagram of Water a mm 200 a so 700 am m1 www sbuzukwnter xm es hase w 300 400 500 Temperalure K Many different solid phases At very high pressure the liquid will solidify P nclpies 0f Chemistry II Mm lam Other Substances 10H Diamond 10quot Graphite Pressure Pa 107 l l 0 2000 4000 6000 Temperature K Figure Copyright Houghton Mifflin Company All rights reserved Principles of Chemistry M C Vainden Bout LECTURE 20 THERMODYNAMIC OVERVIEW A QUALITATIVE APPROACH Today s lecture is a general overview of thermodynamics from a qualitative perspective To really be able to understand thenno you need to look at a chemical reaction and talk about it in the context of relative changes in state functions The lecture actually parallels a hand you can download called Thoughts on Thermodynamics If you can actually learn what is on this handout and be able to explain it unassisted to a classmate you will do well How to Know if a Reaction Happens First one of the important consequences of thermodynamics is the ability to explain whether a reaction occurs or not Note that for every spontaneous reaction there is a reverse nonspontaneous reaction and it would be nice to look at a reaction and tell whether it is going to happen as written or as the reverse For example 2H2 02 g 2H20 6 exploding balloon is spontaneous 2H20 2 2H2 02 6 water becomes H2 02 is not spontaneous The state function that determines spontaneity is free energy AG Rxn is spontaneous Free energy E AG Rxn is not spontaneous So when you look at a reaction if you know it occurs from experience you know it has E AG 9 Example Consider AgNO3 NaCl 9 AgCl Na NO You know from solubility rules that AgCl is insoluble and the reaction shifts to the right so you know that for this reaction AG is Signs and thermo Be the System So what is the source of this idea about thermodynamic signs Why was AG G for a spontaneous reaction defined as spontaneous Is it arbitrary NO How sign convention happens Be the System Sign convention views the assignment of and for thermo processes on the basis of whether the system gains or loses If the system gains the sign is If the system loses the sign is Heat Absorbed Heat Leaves Endothermic Exothermic Bonds Formed System Bonds Break Work Done Work Done On System Bomb is on Surrounding Loaded Bomb EXplodes Good for System Strength Bad for System Strength This Be the System idea can be hard because we are the surroundings and like to think we are what matters But in thermo it is the system Example A Fire Burns Down a Housels the process exothermic or endothermic Is work done on this system or the surroundings Exothermic heat evolves the wood of the house gets cold ie the strong wood bonds become weak bonds COZ HZO bonds Work Done on the Surroundings gas evolves wood becomes COZ HZO A bomb is formed as the volume of the house expan More thoughts on work and signs Note w PAV AnRT Why is the negative sign Note that in a reaction with work done on the system mm om 2H20g An 1 and AV gets smaller But since we know we must be work is being added to the system then the minus sign is needed to correct sign w AnRTRTRT Understanding signs is vital because every thermo answer has a sign and you can do the math and get the right number but choose the wrong sign and get the entire problem wrong Temperature dependence of free energy As we will learn there are two quantities that can be measured to determine free energy in the equation in a temperature dependent reaction enthalpy AH and entropy AS AG AH T AS Case 1 Always spontaneous Conditions for AG 2 AH AG always T AS 9 if 9 an d GD spontaneous Case 2 Never spontaneous Conditions for AG AG AH TAS always non GD if and 9 spontaneous Note T is always so a positive AS makes T AS Case 3 Temperature dependent AG AH TAS 9 if and andT large if 9 and G andT small Example of temperature dependent spontaneity Ice melting H20g 9 H20l Is it spontaneous It is at high T but not as in a freezer So it must be the high T spontaneous case 6 at high T AG AH T AS TAS overcomes AH On to explain Energy in 3 forms AH T AS W work not a state function enthalpy state function entropy state function Describes de done by describing heat of describing disorder of gas molecules reaction reaction First Enthalpy AH AH E enthalpy can be GB or 9 9 E heat given off to surroundings E exothermic Example Ca0 H20 9 CaOH2 heat Cooks an egg makes a mess and AH is G E heat absorbed so surroundings cold E endothermic Example BaOH2 NH4NO3 9 NH3 and other stuff cold and AH is GD In general combustion reactions are exothermic and most spontaneous reactions are exothermic But not all see last example above 39 So we can say exothermicity promotes spontaneity but is not a necessary condition for spontaneity There are 3 ways you will be asked to determine AH o Calorimetry mCAT calculation 0 Heat of formation calculation 0 Bond energy calculation Entropy tendency to disorder In a chemical system AS E entropy increases 9 E entropy decreases As you see from AG AH TAS you want AS positive for spontaneity And this makes sense reactions happen because something is made easier and increasing disorder like creating a messy room is easier than creating order cleaning up a room So can we predict the sign of AS Yes using common sense Increased temperature increases AS Why When it gets hotter kinetic energy goes up velocity goes up molecules i separate more Increased volume increases AS Why If molecules that bounced around in a cup will be more disordered bouncing N around in a gallonJug Solid 9 liquid 9 gas increases AS Why 5 9 Solid Liquid Gas 4 Increased An of reaction increases AS Why More molecules more mess So we can look at a chemical reaction and predict AS 2mg 04g ZHZOCg AS is G Why Two reasons rst An l 3 9 2 so fewer particles made and second g 9 s so the matter is more ordered Work On to work w which is the ability of a chemical reaction to push objects around as in de w If you think about it gas molecules under pressure will exert a force as they achieve large volume w PAV boom as CO as a cozm 9 002m solid C02 1 enclosed container This is actually what mz s a bomb 2 increase in gas pressure Note we only talk about gases because solids 9 liquids don t change volume very much So can we calculate w From the ideal gas law W PAV AnRT gas law and for R 83 Jmole K at 300 K so RT 2 25kJ at room temperature So all we need to do is find Angas and at room temperature work for a gas is a multiple of 25 kJmole Example 2H20g g 2H2 02 Angas 3 2 2 gt w AnRT l83300 25 kJ Example 2H20l 3 2H2g 02g Angas 3 0 3 gt w AnRT 383300 75 kJ See how easy a work w calculation is LECTURE 24 ENTROPY THE TRUTH BEHIND SPONTANEITY We have defined spontaneity through AG AG spontaneous AG non spontaneous But we have seen that reactions can occur 0 whether a rxn is endo or exothermic 0 whether the entropy of a system increases or decreases Clearly something more profound than simple energy conservation from the first law is at work What is the deeper insight The second law of thermodynamic says that A reaction is spontaneous if the entropy of the isolated system increases an isolated system is the universe in most examples We are quite accustomed to disorder in natural environments as the direction of physical processes 0 Food coloring distributes in a beaker of water 0 A hot block of metal cools to room temperature We are less accustomed to understanding this with chemical processes especially when considering reactions that increase the energy of a system endothermic or decrease the entropy of a system the system gets more ordered Like why do we exist The answer rests in a deeper appreciation of entropy on a global level But first we need a quantitative measure of entropy 235 Entropy De ned Quantitatively AS Q in a reversible process at constant temperature Example What is the entropy change if we dump 100 J of heat into a cube of melting ice AS 100 J 273 K 0366 JK Is there a way to describe AS Q T that makes physical sense The key is to realize that is we dump a lot of energy into a system it increases the disorder For example when we explode a hydrogen balloon stuff starts ying everywhere We see the balloon parts all over the ground We feel the rush of hot air past us So increasing Q in a system makes sense for AS increasing But why an inverse relationship to T The equation says 100 J makes a lot bigger mess at l 0K than at 1000 K AS is a lot larger at l K than 1000 K The famous analogy is to sound during an exam versus sound at a concert At a concert if someone coughs it is barely noticed the change in sound is minor But in a quiet room a cough makes you want to punch the guy with a cold 236 Global Changes in Entropy To obtain a quantitative understanding of how entropy affects spontaneity we need to better define a few terms AStotal E change in entropy of the isolated system ASSHIT E change in entropy of surroundings AS E change in entropy of system SO Astotal ASsm And from the second law a reaction is only spontaneous if AStota1gt 0 This suggests that AS for the system can be negative and a rxn spontaneous BUT ONLY IF ASsm gt AS Famous examples of AS negative reactions are phase changes like H20 aq gt H20 1 gt H20 5 which we see happen all the time So we know that if H20 1 gt H20 5 has an increase in ASsuIT driving the rxn Table S for H20 Phase T 1 C 2 S0 gJkmoh Solid 273 3 4 I 0 43 we estimate this with stat thermo Liquid 0 65 Vapor 100 197 50 75 ice freezing has a ASo 22 Jkmol 200 204 100 87 237 So according to the second law if ice freezing is spontaneous below 0 and we see this to be true then AS 05m gt 22 Jkmol at lt 0 K We know ASSHIT amp so at 100 the AHfUSion of ice becomes heat in surroundings 6 000TJmole 263 AHf 6 kJmole for H20 23 Jmole K So ASSHIT gt ASSys below T0 C And thus water freezing is spontaneous Can we make sense of this qualitatively Yes The heat that leaves the system when ice freezes is going into the surroundings conservation of energy But it is going into a colder environment Remember that in a colder place quieter room the disruption is greater Hence the 6000 J of heat are making a bigger relative mess in the surroundings 10 0C than in the system 0 C Exothermic Processes Water freezing is exothermic Heat leaves the system This means that there will ALWAYS be an increase in ASsurr when heat leaves which aids spontaneity even when ASsystem is negative 235 Example 1 Exothermic an Assystem decreases H g H20 1 SW decreases ASM increases tASmis gt 0 E 0 So even though ASsys goes the Wrong Way heat leaves AH makes ASW overcome it Example 2 Exothermic an Assystem increases combustioan CgHgg 5 02 g 3 3 C02 g 4 HZOg ncrease I ASsun Increases ASL 1s gt G gt V here ASSys helps spont d A thermic makes ASsun increase Both AS5V5 AH5V5 make ASmt gt G gt heat leaves But What about endothermic processes How can they be spontaneous How can a reaction happen ifAE for the system gets stronger Isn t the energy going the Wrong Way Answer It s the entropy not the energy stupid Entropy drives spontaneity Example3 Endothermic Process Assystem increases H20 5 gt H20 1 ice melts ASSuIT decreases because AH I AStotisgt0 spontaneous ASsys increases because T in system T L and solid gt liquid heat enters So we now look at these cases of AG in a new light where the AH being endo or exothermic changes AS AHT and either drive or stalls spontaneity 237 238 The rest of the Semester All of Chemistry Today Groups lV Vlll Principles of Chemistry ll imam am Aluminum is a very useful metal Where does it come from All quotBauxitequot to begin with A mix of aluminum iron and silicon oxides quotBayer processquot to purify to only Al203 Alumina rst dissolve in base onlyAl and Si compounds dissolve the lower the temp and A203 is less soluble so it fall out rst Then heat it up with Carbon to get Al C02 Principles of Chemistry Ill ovum Bout The Bayer Process is A The formation of ammonia from H2 and N2 B The formation of nitric acid from NH3 C The puri cation of alumina from bauxite D Used in the production of sulfuric acid Principles of Chemistry ii a mum am Or electrochemical reduction of alumina HallH roult process electrolytic reduction of molten Alea Graphite anude ian camqu Graphlte iiriirig Principles of Chemistry Ill ovarian Bout Random fact of Energy Geothermal energy in Iceland heal amp elecmcal current power plan waisrvmm l l 39 haai d What to do With all that pmdmonwem w w energy Injection well permeable rocks 4 Make aluminum 39 Iceland re nes huge amounts of aluminum exports it geothermal energy Principles MW Ill emu Boric Acid BOH3 H20 gt BOH439 H toxic to many insects Disrupts metabolism and its abrasive NaBH4 Strong Reducing Agent BH439 quotexcess electronsquot W of 511 ll manual nous Ceo nanotubes 483 f quotwrapped upquot graphite Wmd le a mimicny M Mameu Bout Why are we excited about C60 and nanotubes Conducting Soluble in different solvents Strong materials nanotubes Might be useful for electronicsnanotubes drug delivery C60 solar cells C60 sensors nanotubes Filmwbs 6 I ma so Remember Molecular Orbitals 2 2 Mo atoms like H2 3 atoms 0 3 MOS 3 4 MOS atoms n g n MOs atoms 2 lled WWW Metals Insulators Semiconductors conduction band E nergy Mg example 2P I 3423 2s Insulator Semiconductor Metal E 1995 hyme Diision of Chemical Education hr7 American Chemical Society Reproduced with permission from Solid8mg Resources Semiconductors bands are close but there is a gap Need thermal energy to move into unoccupied states Or dopant add or remove an electron 9f lll Mam m Bnm Why is Silicon semiconducting while Diamond is an insulator same structure A Silicon is larger so their is less interaction between the atoms and a lower splitting between the levels B Silicon is smaller so their is less interaction between the atoms and a lower splitting between the levels C Silicon is larger so their is more interaction between the atoms and a greater splitting between the levels 8 M omega sent Graphite is sp2 carbons p orbital SP2 orbital 522 orbital 5172 orbital M o vam e ilhut Diamond and Silicon all sp3 Carbon diamond close atomic spacing leads to strong orbital overlap and large splitting between the bonding and antibonding bands INSULATOR Silicon larger atomic spacing leads to weak orbital overlap and a small splitting between the bonding and antibonding bands SEMICONDUCTOR How mi ht ou quotadd an electronquot to silicon g y Group Iquot Will take an electron and quotleavequot a positive charge in the Si lattice P doping P positive A Substitute a P for a silicon atom in the solid 39Gmu pfv L H 1 El resumng ill a ne 39 B Substitute a Bfor a silicon atom in the solid C Substitue a C for a silicon atom in the solid Lecture 24 Organic Chemistry An Introduction I am not the best person to be giving a lecture on organic chemistry the world is filled with two kinds of people the ones who despise organic and the ones who love it During the year I took organic in college I was also plastering the words from sad songs all over my dorm room walls looking back I realize there was a cause and effect relationship between organic and typing up those songs Honestly I always thought the lunch each Tuesday afternoon before my organic lab felt pretty much like a person going before a firing squad only it happened over and over and over for an entire year With that off my chest here is a nice lecture that surveys the important foundational concepts for the vocabulary that describes organic chemistry Mostly you will get a feel for the fact that organic is a lot of nomenclature and a lot of systematic rules For those who likes languages and lists and for those who can close their eyes and imagine a threedimensional world of molecular structures organic is quite easy For those like me who would rather reduce the subject to a couple of simple mathematical formulas it is quite difficult I mean what kind of science course doesn t need a calculator But enough rant Things you already know about organic just because you took my course As much as I don t like organic the physical basis for pretty much everything you would learn in organic is developed in freshman chemistry some things you need to remember throughout your organic course are 0 Bonding theory like VSEPR VB and MO that allow you to draw the structures even in three dimensions 0 Your friend AEN which allows you to assign local and molecular polarities of the electron clouds and armed with where 8 and 5 assignments across an organic compound let you intelligently discuss physical properties and chemical reactivities with the best of them After all you have worked a huge number of organic chemistry problems throughout the year For example Tell me everything you know about the compound CH3CH20H ethanol To start you are actually capable of drawing this 3dimensional image of ethanol yourself using simple bonding ideas The large grey balls are the carbon the small grey balls are the hydrogen and the red ball is oxygen So what can you already say about this molecule from being a student in general chemistry Plenty All the atoms achieve a Nobel gas structure either ls2 for H or 2s22p6 for the C and O The C and 0 have four electron rich regions which means they have tetrahedral electronic geometry are approximately 1095 bond angles and have sp3 hydridization The carbons have four bonding regions and are either tetrahedral or distorted tetrahedral molecular geometries AB The oxygen has two nonbonding electron pairs and is ABZUZ or angular electronic geometry There are only sigma bonds in the moleculeiin other words all the bonds lie between the atoms Specifically there are 8 sigma bonds5 formed from sp3ls overlap in CH bonds one formed from sp sp3 overlap in the CC bond one formed from the sp3sp3 overlap in a CO bond and one formed from the sp3ls overlap in an OH bond If we were to assign electronegativities H 21 O 35 and C 25 we would find that all eight bonds are polar covalent AEN lt 15 If we tried to sum all the AEN in the molecule we would find that the CH3 methyl region is fairly nonpolar small total AEN in the region but the region around the oxygen is fairly polar as is the overall molecule because of the big electronegativity of oxygen relative to H This polar molecule also happens to possess both instantaneous dipoles associated with the hydrocarbons but more importantly hydrogen bonding because of the H attached to an electronegative atom O This means that ethanol is going to have very strong intermolecular forces 0 Having very strong electronegative forces means that ethanol has a low vapor pressure a high Viscosity a large capillary action and high melting and boiling points among other physical properties related to a large IlVIF Having hydrogen bonds means that ethanol will be miscible in water which is good because it means liquor can be diluted It is also immiscible in most nonpolar materials 0 Those carbonhydrogen bonds love to react with 02 and halogen gases for that matter and a nice combustion reaction with C02 and H20 as products can be drawn Among other things we know that this combustion reaction will be spontaneous exothermic increase the entropy of the surroundings and do work on the surroundings 0 Oh and of course there is an activation barrier to this combustion reaction which is why we have to toss a match on the ethanol for the combustion reaction to happen with a large preexponential factor in an Ozarka bottle and a small A value on a surface like my hand 0 And that O in the 3dimensional picture is red for a reason It screams I have all the electron density This means this is where the action is in a chemical reaction And for those of you who take organic you would do well to draw a 839 near the oxygen and remember that is where the 5 in other molecules is likely to go if given the chance in a reaction Well I could go on and on and on with other stuff we have learned and can apply to ethanol But I will stop and reemphasize two important points 0 You aren t really going to be taught any new chemistry next year in organic 0 Instead you will spend the year doing what I have done above for ethanol for a million other compounds So all I really need to do now is to teach you some nomenclature and you can just go ahead and test out of organic by saying yeah yeah Laude already taught us all that bonding reactivity thermo and kinetics stuff Organic Chemistry Nomenclature Why does it take a year to do organic the study of a single atom carbon The reason is that pesky carbon atom is remarkably adept at forming different kinds of molecules For example if I were to draw all the legal ways to put together 12 C atoms and 26 H atoms to satisfy the Nobel gas configuration there are 355 correct structures each with its own unique properties And then if we let the C react with all the compounds that form covalent bonds like N 0 Cl P S etc the possibilities explode exponentially And organic chemists want you to be able to draw and name everyone of those compounds and then explain why one of them evaporates just a little faster or reacts just a little slower than another So I guess they can have their year But it is still just stuff you learned in my class Alkanes The basic organic compound is an alkane it has only C and H bonds and every one of those bonds is a sigma bond Alkanes are not very exciting because they don t do much reacting But they are a great place to start learning nomenclature To begin every organic molecule has three parts defined by a VERY systematic set of rules a prefix a parent a suffix o The parent is the length of the longest carbon chain like methane for one carbon ethane for two carbons heptane for seven carbons o The prefix contains any substituents on the molecule besides the parent C chain like an extra methyl or hydroxyl group 0 The suffix is the family in which the compound falls based upon the functional group attached to the parent chain for example the suffix ol indicates that ethanol is an alcohol For the first molecules we are studying the alkane family has a suffix ane to indicate that nothing more exciting that a bunch of hydrocarbon sigma bonds are found in the molecule So whether you have Pentane or decane or 2methylpropane or 24 dimethylheptane The ane suffix indicates you have an alkane So what are all the possible parent names Not surprisingly they kind of make sense if you know your Greek and are so consistent that you pick them up quickly even if you don t speak the language TABLE 181 Alkane Nomenclature b r of Name of Name of carbon atoms Formula alkane alkyl group Formula 1 CH methane methyl CH 2 CHECl l3 ethane ethyl Cl ISCl lli 3 CHjClIZCH1 propane propyl CllsCHlCllli 4 CHCl IZZCH butane bury CHCH3JCH17 5 CH3C 13CH pentane penryl CHSCHZSCHZ 6 Cirljujnzncrl3 hexane hexyl 014071940 If 7 CH3CHZ5CH heptane heptyl CllCIIljCll2 8 Cl39l3Clll6Cl l3 octane octyl ClIClllbCllli 9 IH3Cl lZ7CllI nonane nonyl CH3CHI7CH27 IO CH3CHZXCH dec ne decyl CH1CH2XCHZ 11 CHACHZ undccanc undccyl CH CHZ9CH17 12 CHCHZHCH3 dodecane dodccyl CH CH1HCH17 Drawing an organic molecule in two dimensions So a simple five carbon alkane is called pentane and has the following structure CH2 CH CH2 CH3 M 2 Pentane C5H12 H3C Note that in trying to tell people about the molecule you can give the compound a formal name like pentane or you can draw a simple structure in which the bonds between the carbons are shown adjacent to the CH2 and CH3 groups or if you are a real organic chemist you don t waste your time ever drawing C and H since that is 99 of what you have in your molecules anyway and instead you just draw the bonds so zigzag sticks above and let everyone else make a mental note that at the vertices are carbons and that every carbon is fitted out with enough hydrogens to satisfy the octet rule By the way if you wanted you could turn pentane into a nice three dimensional picture just like the ethanol above that is if you wanted to and after awhile you just automatically imagine that 3dimensional picture in your head and don t bother with any more than squiggly lines Adding Substituents t0 the Parent Chain Organic would be very boring if everything was a great big long straight chain How about hanging stuff off of the various carbons Like this EH3 CH3 H3C C CHzCH CH3 CH3 2 To name this more complicated compound you still need to find out what your longest carbon chain is The red carbons point out that this is a compound with five carbons at its longest length So the parent name root is pentane But notice that a bunch of alkane units are hanging off the red carbon chain These are substituents and the table above describes them as various alkyl groups depending on the length This particular compound has three different single carbon alky groups or methyl groups So we need to name this compound something like methyl methyl methyl pentane Except that the carbon unit to which they are attached matters so we probably need to number the pentane carbons Without going into too much detail we try to keep the numbers as small as possible and this means labeling the carbons from left to right in order from 1 to 5 We then end up with the follow compound nameisee if it makes sense to you 2 2 4trimethylpentane I am not going to teach you the 3000000 technical rules about how compounds are names you get that in organic But I will tell you that those rules are very strict and are referred to as IUPAC nomenclature By the way Dr Bard in this department was the head of IUPAC for a long time he is an important guy Also know that long before there was IUPAC organic chemists were assigning common names to compounds that exist to this day So for example what IUPAC refers to as 2propanol you know as isopropanol or better yet rubbing alcohol Structural Isomers Recall that I told you that there were 355 ways you could write forms of CIZHZS Well now you see how this can be done A structural isomer is a compound which has the same molecular formula but a different structure And while smaller chain hydrocarbons don t have many structural isomers for example butane with four carbons has just two structural isomers by the time you reach the C32 alkanes there are about 3 x 107 structural isomers trust me on this As we near the end of the section on alkanes a question can you state a general formula for hydrocarbons oflength n This is as close as we get to math Answer CnH2n2 take a look at the table and you will see it is so Now some chemistry of alkanes Basically alkanes bum and cleanly I might add following the combustion equation below ZCKHZM 3nOz a 2n2HZO ZnCOZ In the table below is a who s who of fuels which are basically hydrocarbons mostly alkanes all of them fractional cuts of petroleum separated by boiling point range as the number of carbons increases And as you can see even though alkanes are the most boring of organic molecules they are the only ones over which people fight wars TABLE 182 Hydrocarbon Constituents of Petroleum Hydrocarbons Boiling range C Fraction CI to C4 I60 0 0 natural gas and propane Ci 0 CH 30 m 200 asoliue Cm to Cm 180 o 400 kerosene fuel oil CF to C12 350 and above lubricants Cl 0 CH lowemelringepoint solids paraffin wax CH upward soft soliLs asphalt Alkenes and alkynes 1l b0ndsisome of you are jumping up and down to ask about the organic molecules we learned about in CH30l that have 71 bonds specifically the carboncarbon double and triple bonds These structures were introduced when we leamed about nbonding the overlap of electron density above and below and in front and behind the central atoms Organic easily these 1 which are given the designations alkene and alkyne with corresponding iene and yne suf xes In the two examples below identify the number of O39 and 7t bonds for old time s sake And note that the same attention to numbering and root names is in place as for other organic molecules 17 6 and 1 7r bond 6 6 and 2 7r bonds CH2 CH CH3 CH crf H3C C CH 8 Propyne CH3CCH H3C 5 3Hexene CGH12 Let s get cyclic A bit more nomenclature involving hydrocarbons It is possible for a molecule to form a loop on itself These are two kinds of cyclic compounds Cyclic hydrocarbons are known as cyclic compounds and we designate them with the prefix cyc o 16 Cyclohexane C5H12 Benzene and its aromatic friends The really important cyclic species are aromatic compoundsithose based on the ring structure shown below 31 Benzene CEH6 As we learned while discussing molecular orbital theory in CH301 aromatic compounds are hexagonal ring structures formed from the overlap of CspzCspz that form 039 bonds What makes aromatic compounds is the leftover 6 electrons that form a sea of delocalized TE electrons positioned above and below the ring It is this pbonding structure that creates a unique stability and reactivity for aromatic species While we won t spend any more time on these structures it is enough to know that aromatic species are ubiquitous in nature whether in petrochemicals like anthracene or drugs like Tylenol or biologicalactive molecules like adenine CH3 NH2 A N quotH quotkD N N H 33 AnthraceneC14H1o 0H 14 Tylenol 22 Adenine Other functional groups in organic molecules Rather than methodically work my way through all the suffixes for organic molecules besides ane I think I will simply provide you with a nice table listing them Note that it you want to have each suffix explained in mindnumbing detail take an organic course oops my bitterness about that time of my life is oozing through Now don t paniciI list them all here straight from Wikipedia because your book doesn t think a table of functional groups is useful so that those of you salivating over starting organic can have at it over the summer For the rest of us the ten or so highlighted in red are the ones I will test on What is most important to note are the prefixes and suffixes that will surround the family name largest carbon root Also note that there are often two names for the compounds the result of common name usage dying only very slowly in the traditional world of organic chemistry M Group Formula Strum Prefix Suffix Example class Formula 0 o A Acylhalide Haloforrnyl RCOX i haloformyl oyl halide CI R X Acetvl chloride Ethanoyl chloride H H RO HC O Alcohol Hydroxyl ROH H hydroxy ol H Methanol O o A Aldehyde Aldehyde RCHO oxo al H R H Acetaldehyde Ethanal 3 w Ammes Alkyl RH Alkenyl R2CCR2 Auqmyl arb met A mu 2 ana m2 amme Secondg RZNH amme T 1 KEN amme 4 ammomum RAN xon Azxde RN F R N w W N H R H H R N R Ry RAN R r th alkylr alkenylr alkynylr carb examde ammo ammo ammo ammomor azxdor Vane rene ryne ramxde ramme ramme ramme rammomum alkyl mag m Memmm me H kn DxmeLhylamme N Tnmethylamme 740H Cholme x azxde hen 1 Azxdob enzme 1 hydroperoxv alkvl de 1 1 n o r hydmpemxide Mem 1 am 1 kewne gerox1de Pnng 7 6mm RCGNTDR 1rn1nor dmme M RCN39RR 1rn1nor dmme eumme mee Pnng 7 aldmne RCGNTDH 1rn1nor dmme W RCN39R H 1rn1nor dmme ald1m1ne Irmde m1de gamma 1 V 1m1dor r1m1de Isocyamde sogamde RNC 1socyanor alkylisucyznide N H3C c soganate RNCO 1socyanawr alkyllsncyznzte 150C mates Methyl 1sogzanate sotmogan RNCS 1soLh1ocyana alkyl N M 039 mmymm A11y11soth1ogana1e O Ketone Carbonyl RCOR k kemoroxor rone R R2 Menu 1 em 1 kewne 511mm N1Lrate 11mm RONO o TOOXVquot alkylnitrzte 2 n c k V o m oxy Am 1 mme Lmtraaxypemane 7quot N1Lr1le 1m1e RCN cyanor alkanenmfk alkyl cyade Benzommle Nxmte 1Lrosoox1 Nxtro m comgound Nxtroso 1Lroso comgound Peroxxde Pao Benzene denvauve m Phosphme Phosphmo Phosphodxes a n M Phosphomc Phosphm M Phosphate Phosphate RONO Van RN02 R xk 0 RNO RN Va R ROOR o q R RCEHS R3 a 2 HOPOOR2 clawR mm RPOgtOH2 R F H 0 o V P on 0 EH mtrosooxyr mer er0507 PemXY39 phmylr phosphmor phosphonc acxd d1ubtztuen t ester phosphonor phosphor alkyl nitrite HPhenyt Cyamde 1 mmte Mew1 mrrasaaxybutane H o H 0 1LromeLhane o i 4 1Lrosobmzene lkl 39d K a y pm 3 Dxrtatrbutyl gaoxxde rbenzme Cumene erwwl rapane 39ph sph e Memylpmpylphosph ane axmrmm ate n substtment 39 f nh nh m vi acxd ee 1 G1 cemldeh de 37 ghoghate 4sp39y39rld39y39l pyrldlnAr Y1 3spyrldyl Egrldlne dmvame Pmdyl RC5H4N gimme spyndlne Zspyrldyl erldlanr V1 s dlwbstltuent Ah m RSR R R39 sul de DlrneLhylsulflde 0 IO Sulfone Sulfonyl RSO7R 0V0 sulfonyls d wmmm S R R Sulfone DlmeLh39y39l sulfone Mcmpsumouptmcm LE 0 o V Sulfonlc Sumo Rso s sum munacut an M R OH sulfnmc and O 0 Hub gt g H V 1 mm Sulfoxlde Sulflnyl RSOR RSRv sulfmyl mmmide g hph Dlphenyl sulfoxlde Th l s lfhyd l RSH R S macaw Lh l ASH i sulfanylr 39 lhanelhiol mpzmmpm u o Alcohols Ethane plus 701an alcohol make ethanol a 2 carbon alcohol o Aldehydes pemahe plus ial aketone make pentanal as carbon ketone o Carboxylic aci s Dodecane plus roic acid a carboxylic acid makes dodecanoic acid a 12 carbon at u u i r we dhave 2 2 4trimethylpentane a 2 2 4trimethylpentanol Organic Chemistry Reactivity What makes organic such a challenge isnlt simply being able to assign names to compounds it is being able to predict the reactions that this incredibly broad array of compounds undergo To say an understanding of organic reactivity is beyond the scope of this course is about as understated a comment as one can make To understand organic reactivity is to understand the chemistry of not just these relatively small molecules but also the fields of polymer chemistry and biochemistryiyou know pretty much everything But we can create three classes of general reaction mechanisms They are listed below in some nice pictures from the text that suggest why the names are given to these reactions Elimination gt Addition gt J C And that is more than enough to know about organiciexcept that we can make a lot of large polymers and biopolymers with them as we will discuss in the next lecture
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