PRINCIPLES OF CHEMISTRY I
PRINCIPLES OF CHEMISTRY I CH 301
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LECTURE 15 MORE ADVANCED IDEAs INVOLVING GASES How fast are gas molecules From kmt T on E 12 kT temp term 12 mv2 velocity term Note that the velocity is easily determined from E 12 mv2 Also note that the higher the temperature the higher the velocity Depending on the mass and T gas molecules more at hundreds of miles per hour at room temperature I Fractian v m s n A 0 00 IUD BUD 400 500 600 Speed msquot Also note that there is an inverse square relationship between molecular speed and mass that falls out of the equation Example At a certain temperature H2 is traveling 1000 mph how fast is Oz moving at that temperature Energy is the same so 12 mm v2H2 12 mm vzoz 4 2 v2H2 32 vzoz 4 322 v2H2v202 4 16 1000 H2 v 02 4 square root 4 1000v so v 250 mph 203 Diffusion and Effusion We know that gas molecules don t really move at hundreds of mph If they did smells would come and go much faster Actually at atmospheric pressure constant collisions occur and the actual speed is reduced many orders of magnitude at atmospheric pressure So what do they call this collisional velocity Diffusion And a similar kind of velocity that has to do with the ability ofgas molecules to get through a pin hole is called effusion diffusion effusion The good news from a calculation perspective is that while the math is much more difficult when looking hat the same inverse square relationship In both cases the rate of effusion and diffusion is the same inverse square relationship as speed So the 4 fold slower velocity ofOz than H2 is also a 4 fold slower diffusion and effusion 204 NonIdeality of gases Is kmt awed Recall that in the introduction to gases we learned that according to kmt gas molecules have no volume gas molecules are not attracted to each other all collisions are elastic But in practice neither statement is completely true Gas volume is not zero Consider whether a gas atom or molecule takes up physical space Of course it does and we can actually see this when we pour liquid nitrogen over a balloon and watch the gas liquefy skullde 4 m 3 an Note also bigger molecules take more space and are less ideal A Ar a we He 205 Attraction between gases occurs Gases bump into each other and stick not a lot but some So the collisions are actually somewhat inelasticinot much or they wouldn t be gases but some As we will learn in Chapter 5 the bigger the molecule the more sticking and the more polar the molecule the more sticking Why does this matter It reduces the number of particles hitting wall and consequently P L MO I l Q Q a mtg 0 Ch 2 mr 0 1 xi so ash ch mimic M Correcting for nonideality How do we correct Fudge factors x non ideality PV i nRT a P Fudge Factor V Fudge Factor nRT P attraction issues T equation for non ideality V volume issues There are many versions of non 7 ideal gas laws The Vanderwaals equation is one P n2a v2 v nb nRT In the equation a and b are fudge factors that are dependent on the kind of gas 206 The bigger a and b the more non ideal For example for He a 0034 and b 0237 These values suggest that He is small and not attractive for NH3 a 417 and b 371 These values suggest that NH3 is bigger and really sticky So when is a gas more ideal at high temperature and and low pressure fewer collisions occur so the gas behaves more ideally for small non polar gases the volume taken and the attractive forces in the collision are small and so the gas behaves more ideally Summarizing Trends For small gases like He and H2 PV nRT is a fine equation to use because the gas is more ideal due to less attraction and less volume For large gases like C02 0r H20 P n2a v2 v nb nRT is the better equation because the gas is less ideal due to stronger attraction and greater volume Other trends For small gases For larger gases Faster speed slower speed Faster diffusion slower diffusion Faster effusion slower effusion 207 LECTURE 7 AN INTRODUCTION TO THE CHEMICAL BOND A summary We use the concept of valence electrons surrounding atoms to create 2dimensional structures in which species with chemical bonds are more stable than bare atoms We base the stability argument for chemical bonds on the generation of species that have achieved stable noble gas configurations s2p6 One kind of bond is ionic electrons are donated or accepted to create anions and cations that have s2p6 configurations A second kind of bond is covalent and occurs when nonmetal atoms share electrons Many compounds achieve s2p6 configurations by sharing electrons in overlapping p orbits to form double and triple bonds as well as resonance structures Bonds can form even when s2p6 configurations are not possible Atoms like boron have 3 valence electrons and usually can fOI H l only 3 covalent bonds with just siX electrons Compounds that contain an odd number of electrons form radicals that can t satisfy octet Larger atoms n3 and higher have available d orbits to hold five and siX bonds Many compounds can have multiple lewis structures that satisfy the octet rule It is possible to evaluate the formal charge of atoms in the resonance structure to find the lowest energy most stable structures Electronegativity is a measure of the pull that an atom has for electrons in a chemical bond Calculation of the difference in EN assists in distinguishing ionic and covalent character of bonds Trends in bond energy and bond length can be predicted Multiply charged bonds are higher energy and shorter Some last periodic table trends as we say goodbye to elements and take on bonding As We leave atoms and take on bonding We need to have Impact on materials 7 main group s and p Valence Wu mer mm Mel1H1 S These main group materials exhibit Very distinct changes by group This makes for easy chemistry to teach Trends are actually present Speaking of trends a new one metallic character is in the main group elemenw Note that Cs is most metallic that the entire le side of table is metallic The right side is more nonmetallic but in groups as you go down metallic character increases Example 02 is nonmetal gas39 S is nonmetal gas Te and Po are metalloids Transition metals d block elements are a mess There are no trends properties are similar they all look like metals This makes teaching them awful in this course Why are transition metals so similar 0 The d electrons are inner electrons and since they are what change nothing much happens to valence e and properties are the same Can this be good 0 Similar atomic radii means we can mix and match to form allows with neat properties 7 like superconductors 0 Lots of oxidation numbers mean e transfer in biological systems On to Bonding A Comparison of Covalent and ionic Bonds The big picture We create 2D Lewis structures by generating Lewis structures of atoms with valence electrons assigned o 39 A O 39 a u 39 9 o H F C le 3976 f I e 96 And mixing and matching to form chemical species in which the duplet or octet is satis ed A Bond What happens when two electrons are placed in an orbit and the overall energy is lowered Example 9 H has nl shell lled C has n2 filled I 3 I 6 Shared electron pair There are two kind ofbonds Ionic in which there is a donation of electron and covalent where there is a sharing Na has n52 shell lled F has n2 shell lled This is anionic bond C has n2 lled O has n2 lled This is a covalent bond Theory ofionic bonds Na g C1 g EA ofCl is E ofNa is 349 K 494 K c1 g Nag c1g9 Nag Nag cl39g Is not favored We want to know if Nag Clg 9 Nat C17 is energetically favored So that Nag Cl g 9 NaCl s is 642 KTmole Wef it i favofge cause lattice NaClTNa J because of all that Coulomb attraction happens energy 01quot c1 Nac1 NaCl salt numer salt crystal is made cm s mmm oem m n mmm m mum m nxm 63 Wk A W3 1 W7 x M T X EMK Twni a 9 possible neutral forms of ionic salts Nacl X Y 6 group land 7 C2109 X Y 6 group 2 and 6 N9 X Y 3 group 3 and 5 Na209 2 X Yquot egroup lando Cacl 2Y egroup 2and7 L13N9 3X 3Y 6 group land 5 AlF X3 v 3 7 group 3and7 CaZN 3X 2Y 3 6 group 2 an 5 So as an example A12039 2X 3 sf 6 group 3 ando The general structure ofLewis ions is MX Him All e removed makes e added makes anion cau39orr 52p6 2po Time Out for an aside on Lattice Energyquot We can develop a reasonable argument from charge density considerations that explains the magnitude of lattice energy Consider four ions Li We can rank the charge density gt Be gt Be2gt Mg2 gt Ligt Na Na Mg gt Higher Lower Charge Charge When we take ions like this and combine them with anions the higher the charge density the closer the bonds and the higher the crystal lattice energy is weaker than 2 2 Example rank the lattice energy of 2 2 NaF KCl MgC12 Singly Multiply high MgC12 gt NaF gt KCl low Charged Charged multiple single charge charge low density Study Strategies in Dr Laude s General Chemistry Before we start time out for Thoughts on being an Active Learner rather than Passive Learner Note that the procedures developed in this handout are among a million ways you might do things However they all fall in the category of ACTIVE LEARNING Whatever you do be an ACTIVE LEARNER Example of a passive learner Reads the chapters from beginning to end Works the homework problems with answer keys or similar problems readily available Blah blah blah Just like always in every class But most importantly has no evidence that anything is actually learnediinstead assumes that by reading the chapter and doing the homework and coming to class that everything is learned Active Learners Constantly assesses what is understood and what is not understood Comes to class aware of what will be covered and knowing what is not known Comes to office hours with speci c questions about a lack of conceptual understanding Targets the speci c content material to be learned Has a way of proving that the material is actually known Assesses testtaking and content problem areas from previous exams and quizzes Creates realistic test taking simulations How to get an A in CH301 and CH302 First Know Yourself Second Know Your Exam Once this is done Know Your Subject Part 1 Knowing yourself as a test taker Ask the following questions about each test or quiz 0 Did I feel I knew the material going into the test 0 Was I happy with my studying habits 0 Did I use time wisely on the test 0 How did I feel about my performance while I was taking the test 0 How did I feel right after the exam or quiz 0 How did I feel after I received my grade Based on the answers to these selfanalysis questions diagnose the follow symptoms Symptom Comes to test poorly prepared and does badly Diagnosis Immature study habits or misplaced priorities Symptom Come to test con dent but soon realize that you cannot work many of the problems Diagnosis Poor calibration of what needs to be done to succeed on a collegelevel exam Symptom Comes to class prepared but quickly develops stress and timemanagement issues Diagnosis This student tends to blame testtaking anxiety but often offers this as an excuse for not really being con dent about the material Symptom Moves con dently through exam and leaves certain of a good grade only to be disappointed by results Looks back at material and blames it on stupid mistakes There are two kind of students who have this experience Diagnosis 1 One type is overcon dent about their knowledge base They are good students who know 90 of what is needed but on a multiplechoice test that is only enough knowledge to select an incorrect but pretty close answer These students have miscalibrated the amount of learning necessary to be successful This student is so bound by rules that if questions are even slightly different from previous material then they miss them This is the student who most of ce blames the instructor for bad questions rather than looking in the mirror Diagnosis 2 The second overconfident student really does know the material but has no interest in playing the game to do well on an exam This student shows up with the wrong number pencil a calculator with a dead battery and no scratch paper This kind of student believes that nishing rst is more important than getting the problem right You know who you are it bothers you when you see other people leaving not because your are nervous about nishing but because you don t want to believe other students know the material better and faster This kind of student misses negative signs and units doesn t see the word NOT thinks small to large instead of large to small This kind of student would never dream of actually checking workyou may you will but deep inside something is screaming you don t need to do this you don t make mistakes By the way I know this last kind of student well because it is me Oh and don t atter yourself that you are in this category Being is this category is to suffer the sin of arrogance Also to be in this category requires that you really do know the material and the vast majority of students do not Developing tangible solutions based upon Who you are First Obtain old exams and quizzes Next to every missed question on an exam or quiz ask the question why did I miss this problem What was I thinking at the time Was I overconfident was I guessing Was I freaking out If I missed it because I didn t know the content why is that Did I believe I knew the material when I did not Did I not study material in that section as well as in other Look for patterns in your mistakes When you see the reason ask yourself what can I do to not make that mistake again Maybe you missed the material that was taught at the end Maybe you missed the material that was taught at the beginning Maybe you missed the material that you learned while riding in a car to Dallas Second Based upon what you glean from an honest assessment of your exams make lists of ways you make mistakes in exam preparation and ways you make mistakes in test taking Sample list for exam preparation I learn best when I go to the Thursday help session I learn best when I study in the library I learn best when I work the problems in Davis first I learn best when I read the notes just before class Now make your own list for exam preparation Sample list for test taking to be considered before every question you answer I will always make sure I look for the correct units especially kilograms to grams I will make sure I see if the answer is ascending or descending order I will make sure I hit the exponent button on the calculator I will make sure that I enter the numbers on a calculator twice I will make sure I rule out clearly incorrect answers before working calculations Now make your own list for exam preparation Part 11 Know your exam You take multiple choice exams based upon specific problem types identi ed in class So develop a strategy that works for this kind of test Here is an approach in two parts First Learn the material from the perspective of content areas that will be on the exam rather than by learning all the material in a serial fashion Question A man stands outside the library and says you can answer the question I ask in one of two ways First you can go in the library and read every book and then come out and I will ask you the question or I can tell you the question and then you can go learn the answer Sadly most of you learn the first way though you don t realize it You act as if you need to learn everything cover to cover and from the first problem to the last rather than knowing what you need to know Solution One solution is to create individual cards on which you place all the information about a speci c question Whether you learn this material in a lecture from a friend from a HW from the Internet write it down on the card That way you are localizing all the material for what you know will be a test question Then when the test comes all you see in front of you is the card with the information on it rather than a blur of dozens of hours of lectures and studying for the entire exam This is no different than what you do naturally for the things you know well I know sports But I don t know it because I memorize every fact from Sportscenter or the paper in order Instead when I read something new I immediately put it onto the appropriate index card in my case the index cards are in my brain Cards like Oakland Raiders or my lovehate relationship with Steve Sparer So every time you see a new set of content areas like in every musings create a new card That way you study for an exam with a handful of cards in your hand not a zillion pages of notes and answer keys A picture of how information you process finds its way on to cards An example of a card on electronegativity Second Prepare for the way an exam is given These multiple choice exams are random collections of problems You may know what is coming but you don t know the order And you don t know for sure that when you read a problem you know exactly what type it is you don t know the type of index card to pull into your brain To develop this ability practice it Get a Wal Mart bag Make a photocopy of your exams and quizzes Cut the photocopied exam into individual questions Jumble the questions up in the Wal Mart bag Remove them randomly and try to guess the problem type the index card Do this over and over until you are able to instantly identify the type of problem On the exam you will nd that magically a little voice in your head will start whispering the problem to you every time you start to work a problem AN INTRO TO THE DESCRIPTIVE CHEMISTRY To this point in our review we ve worked on methods for establishing a QUANTITATIVE foundation in chemistry We can now manipulate all manner of unit factors to solve problems involving amounts of chemical materials and while there was some modest requirement that you understand the nature of the substances involved in the problems you might just as well have applied the techniques you learned to solve problems associated with preparing a good white sauce make the units cancel and you ve learned the right answer whatever those numbers meant There was nothing particularly relevant to chemistry in the problem solving Well now there is a radical change in material For one thing there aren t any problems to work Reading this material is like taking a botany class Suddenly our primary focus is on DESCRIBING chemistry So when you get down to it in this chapter there is a whole lot of MEMORIZING going on But I will also introduce you to the basic theoretical foundation that signi cantly reduces memorization by learning the following basic concepts Concept 1 Periodic Trends Like Metallic Character 0 You learn basic trends in the elements that prompted the creation of a periodic table of those elements The first is which elements are metals and which are not Concept 2 Acids Base Chemistry 0 You will learn what things do and don t behave as acid and bases Concept 3 Which Ions dissolve in Water 0 You will learn elementary solubility rules for ions in water Concept 4 OxidationReduction 0 You will learn to assign oxidation numbers to elements The oxidation number is you first indication of where ELECTRON DENSITY is located in chemical compounds Concept 5 Active Metals 0 You will learn about displacement reactions which means you will learn to predict what happens when you dump metals into water Concept 6 Chemical Nomenclature 0 You will learn the common way to name binary and ternary ionic compounds A hint don t memorize compound names memorize naming rules The Periodic Table Long about 1870 Mendeleev was inspired to put together a tabulation of the known elements in such a way as to describe in a periodic way their physical and chemical properties The modern version of Mendeleev s Periodic Table is an attractive addition to most science lecture halls it is worth studying during drier moments of lectures if for no other reason than to prepare for chemistry tests Families of Elements Note that the table of elements consists of columns groups or families of elements in which similar properties are observed Group IA alkali metal Li Na K Rb Cs Group HA alkaline earth metals Be Mg Ca Sr Ba Group VHA halogens F Cl Br I Group 0 noble or rare gases He Ne Ar Kr Xe Periods Chemical Trends along Rows ofElements You can also look at the table as a collection of horizontal rows called periods Row 2 Li Be B C N O F Ne As we will leam important trends in chemical and physical properties are observed as we move across a row For example Trend 1 Metals and Nonmetals We will look at numerous trends within the periodic table during the semester Our first trend will be with respect to metallic character in elements Note in Table l the qualities of metals Table 1 Some Physical Properties of Metals and Nonmetals Metals Nonmetals 1 High electrical conductivity 1 Poor electrical conductivity 2 High thermal conductivity 2 Good heat insulators 3 Metallic gray or silver luster 3 No metallic luster 4 Almost all are solids 4 Solids liquids or gases 5 Malleable 5 Brittle in solid state 6 Ductile can be drawn into wires 6 Nonductile Your rst periodic table trend Metallic Character increases from right to left and top to bottom Thus Cs is the most active metal Note that most elements are metals Nonmetallic Character increases from left to right and bottom to top The most active nonmetal is F Metalloids The switch hitters of the world along the interface between metals and nonmetals These include elements like B Si As Ge You may notice that the world of semiconductors revolves around the metalloids Aqueous Chemistry If there is one molecule worth giving too much attention it is water Water makes up 75 of the earth s surface 70 of the human body and 100 of a Diet Coke It is not surprising then that so much effort is devoted to understanding the chemistry of water ahnost every reaction we will examine between now and the end of the course will occur in water Electrolytes Ions Moving Through Water The chemistry of water is primarily the chemistry of dissolved ions Water is a polar solvent with the ability to promote the dissociation of ions One property of these ions conduct electricity in water Strong Electrolytes Compounds that dissociate completely in water to form ions are called strong electrolytes Examples of these include alkali metal salts and strong acids and bases NaCl 9 Nal Cl39 KNO3 9 Kl NO339 HC1 9 H Cl39 NaOH 9 Nal OH39 We assume that essentially 100 of the salts or acids of strong electrolytes dissociate to form ions Weak electrolytes Some compounds dissociate only slightly preferring to remain primarily in an undissociated form These molecules are referred to as weak electrolytes and include a wide range of sparingly soluble salts as well as weak acids and bases AgCl 9 Ag 0139 Caco3 9 Ca CO3 CH3COOH 9 H CH3COO39 Nonelectrolytes Of course there are molecules that are too tough to have their bonds ripped apart in water These are molecules like sugar which possess covalent rather than ionic bonds Water may be capable of solubilizing these molecules dissolving them but no ions are formed and electricity is not conducted in solution SUGARS gt SUGARW Note that ions are not formed but the sugar is dissolved in the water aq means aqueous Acid Base Chemistry What is the big deal with acids and bases Again it is because we are working with water which as we will see has its own chemistry that produces ions like H and OHquot and which as everyone knows are what Arrhenius called acids and bases Consequently we will spend a lot of time looking at what happens with these two ions the proton or hydronium ion Hl and the hydroxide ion OHquot In CH 302 we will develop many equations that attempt to determine their concentration in solution their pH But again understand the context we are working in water and we are examining electrolytes In other environments H and OHquot would have no significance For example how often do you hear people talk about the pH of gasoline BronsteadLowry De nition Acids and Bases acid capable of donating a proton base capable of accepting a proton The general equation for the dissociation of an acid is simply HA gt Hl A39 For example HC1 gt Hl C139 or CH3COOH gt Hl CH3COO39 TABLE D39l Common Anions and Their Parent Acids Anion Parent acid Anion Parent acid fluoride ion F chloride ion Cl bromide ion Br iodide ion I oxide ion 01 hydroxide ion OH sulfide ion 52 hydrogen sulfide ion HS cyanide ion CN acetate ion CHSCOZ carbonate ion C032quot hydrogen carbonate bicarbonate ion HCQ hydrofluoric acid HF hydrogen fluoride hydrochloric acid lICl hydrogen chloride hydrobromic acidan IIBr hydrogen bromide hydroiodic acid HT hydrogen iodide water H20 hydrosulfuric acid H25 hydrogen sulfide hydrocyanic acid HCN hydrogen cyanide acetic acid CH3COOH carbonic acid HZCO nitrite ion NOl nitrate ion NO phosphate ion POX39 hydrogen phosphate ion HPOf dihydtogen phosphate ion HZPOI sulfite ion 5031 hydrogen sulfite ion HSO sulfate ion 5041 hydrogen sulfate ion HSO hypochlorite ion ClO chlorite ion 10 chlorate ion CJO3 perchlorate ion C104 39The name of the aqueous solution of the compound The name of the compound itself is in parentheses Distinguishing Strong and Weak Acids and Bases nitrous acid HNO2 nitric acid HNOS phosphoric acid H3PO4 sulfurous acid H1505 sulfuric acid IZSO4 hypochlorous acid HClO chlorous acid HClOl chloric acid HCIO3 perchloric acid HClO Now just as there are strong electrolytes which dissociate completely and weak electrolytes which only partially dissociate there are the equivalent strong and weak acids and bases 0 Strong acids are strong electrolytes 0 Weak acids are weak electrolytes The definition of a strong or weak acid When we start to do a lot of problems involving acidbase chemistry it is important to be able to distinguish which compounds are strong acids and bases and which are weak acids and bases Remember that something is de ned as an acid or base in water by an ability to donate a proton or hydroxide respectively Whether a compound is a strong or weak acid or base has to do with the extent to which it dissociates Strong acids and bases Compounds that are assumed to dissociate completely upon addition to water HA 9 Hl A39 initial 100 0 0 equilibrium 0 100 100 Common Strong Acids Anions of These Strong Acids Formula Name Formula Name HCl hydrochloric acid Clquot chloride ion HBr hydrobromic acid Brquot bromide ion HI hydroiodic acid Iquot iodide ion HNO3 nitric acid N03quot nitrate ion HClO4 perchloric acid C104quot perchlorate ion HClO3 chloric acid C103quot chlorate ion H2804 sulfuric acid HSO439 hydrogen sulfate ion How do we know which compounds are strong acids or bases We memorize the table Weak acids Of course if an acid or base doesn t dissociate completely it behaves as a weak electrolyte Most of the acid stays in the molecular form Only a small amount dissociates to form a proton and the anion CH3COOH Hl CH3COO39 initial 100 0 0 equilibrium 99 l 1 How do we know which acids are weak Simple It is any acid that isn t one of the seven strong acids Several examples are shown in the table above Bases We can describe an analogous collection of strong and weak bases that produce OHquot in aqueous solution The strong bases include the Group IA and HA metal hydroxides For example N OH a Nal OH39 Initial 100 0 0 equilibrium 0 100 100 Table of Strong Bases LiOH lithium hydroxide CsOH cesium hydroxide NaOH sodium hydroxide CaOH2 calcium hydroxide KOH potassium hydroxide SrOH2 strontium hydroxide RbOH rubidium hydroxide BaOH2 barium hydroxide Weak bases If a base is a weak electrolyte it does not dissociate significantly in solution The most famous weak base is ammonia NH3 NH3 NH OH39 initial 100 0 0 equilibrium 99 l l Solubility Throw a compound into water Does it dissolve or does it sink to the bottom of the ask Whether this happens or not determines the SOLUBILITY of a compound A soluble compound dissolves An insoluble compound usually sinks to the bottom of the ask as a PRECIPITATE although it may fOI H l a SUSPENSION in solution For the most part we are interested in what ionic compounds do in water How do we know what these ionic materials do in solution We learn rules about solubility see the next page Solubility of Common Ionic Compounds in Water There are two ways to learn the solubility rules 0 Memorize the individual solubility rules for each kind of cation and anion The two tables below list the ions that are generally soluble and the ions that are generally insoluble If the thought of memorizing a lengthy table makes you sad see if you can spot some generalizations that make it easy to slide by with some simple rules that account for most of the ion solubilities TABLE ll Solubility Rules for Inorganic Compounds Soluble compounds Insoluble compounds compounds of Group 1 elements ammonium NH439E39 compounds carbonates CO32 eliminates CrO4l chlorides Cl bromides Br and maladies C20427b and phosphates iodides 1 except those of Ag Hg22 PO43 except those of the Group 1 and szar elements and NHf nitrates NOB gt3 acetates Cchoj L sulfides 82 except those of the Group 1 chlorates ClO3 and perchlorates and 2 Elements and NH ClO4 hydroxides OH and oxides 02 sulfates SO 27 except thOse of Ca2 except those of the Group 1 and 2 elementsiF 4 a 9 SrH Bay Pb Hg22 and AgJr PbCl2 is slightly soluble 1 AngO4 is slightly soluble i CaOHZ and SrOH2 are sparingly slightly soluble MgOHl is only very slightly soluble There has to be an easier way Some cation solubility rules 0 Rule 1 All of the alkali metals Kl Nal etc ions plus NH4 are always soluble 0 Rule 2 Heavy cations down the periodic table like Ball and Ag and Pb are insoluble Some anion solubility rules 0 Rule 3 Anions that are always insoluble except for Rule 1 are mostly the multiply charged species S CO P043 0 etc 0 Rule 4 The anions that are primarily soluble are the conjugate bases of strong acids like Cl39from HCl Brquot from HBr N03quot from HNO3 ClO439from HClO4 etc These rules aren t perfect but they are good enough to get an A in CH301 without doing a lot of memorizing The Best Solubility Rule of All But the biggest trend of all the rule of thumb if you only want to remember one thing is this the singly charged ions are usually soluble and the multiply charged ions are usually insoluble The reason for this is something we will learn in CH 302 Solubility Example We can use this information to decide the types of reactions that occur when we place compounds in solution Consider the reaction of CaNO3 and KCO3 Note from above that nitrates and alkali metals are soluble So when these compounds are added to solution four ions are formed Ca NO339 Kl CO3 Note from above that carbonates are generally insoluble so it is expected that the following precipitation reaction occurs Caaq C03 1 quotquot39gt caCO3 S Oxidation Numbers Reactions in which substances undergo changes in oxidation number are called oxidationreduction reactions or redox reactions Redox reactions involve the transfer of electrons Some definitions 0 oxidation an algebraic increase in oxidation number in which electrons are lost from a compound 0 reduction an algebraic decrease in oxidation number in which electrons are gained from a compound 0 oxidizing agent substance that gains electrons and oxidizes other substances by being reduced 0 reducing agent substance that loses electrons and reduces other substances by being oxidized Oxidation Rules Assignment of the oxidation number for a compound follows certain rules 1 The oxidation of a free element is zero Na is 0 2 The oxidation number of an element in a monatomic ion is the charge on the ion Na is H 3 The charge of a monatomic ion is usually determined by its group column on periodic table See table below 4 In the formula for any compound the sum of the oxidation numbers of all elements in the compound is zero NaCl is 0 5 In a polyatomic ion the sum of the oxidation numbers of the constituent elements is equal to the charge in the ion N0339 is l Some oxidation numbers for each Examples of Oxidation Number Assignment 1 5 2 1 4 2 1 1 5 2 Na N 03 K2 Sn H6 H3 P 04 42 1 42 6 2 s 03392 H C 0339 Cr207392 Displacement Reactions The world is filled with two kinds of metals those that dissolve in your pants and those that don t Coinage metals like gold silver copper don t dissolve in your pants or when you bury them in the ground This is why they are so valuable But valuable also means boring If you want real fun you hang out with active metals like potassium and magnesium and lithium active metals that explode at the slightest provocation like placing them in water So what does happen when you throw a metal in water MH209MH2OH o The metal is oxidized becomes a cation 0 The water is reduced making hydrogen this is why Na explodes in water 0 The water turns basic you can see this with an indicator turning color Wow what a famous reaction There is a special kind of reaction in which one element displaces another element from a compound For example CullSO4 Zn gt ZnSO4 Cu In general active metals displace less active metals and hydrogen There are three categories to consider 0 Reactions that displace hydrogen from nonoxidizing acids 0 Reactions involving metals that displace hydrogen from steam 0 Reaction of metals that displace hydrogen from cold water These results are tabulated below Type I Elements Common Common Reduced Form Oxidized Forms Li Li Lil K Displace hydrogen K K Ca from cold water Ca Ca2 Na Na Na Note these elements are the ones that eXplode in water Type 11 Elements Mg Mg Mg2 Al Al Al3 Mn Displace hydrogen Mn Mn2 Zn from steam Zn Zn2 Cr Cr Cry Cr6 Fe Fe Fez Fe3 Type III Elements Cd Cd Cd2 Co Displace hydrogen Co Coz Ni from nonoxidizing acids Ni Ni2 Sn Sn Sn2 Sn4 Pb Pb szi Pb Type IV Elements Cu Cu Cu Cu2 Hg don t react Hg Hg22 Hg2 Ag Ag Pt Pt Pt2 Pt In reading the metal activity table the metals at the top of the chart displace salts of the less active metals below them An easy way to think of this a reaction occurs if the more stable metal the one lower on the chart is a reaction product Again what are some of the general rules you might use rather than have to memorize everything The farther to the right the more reactive the metal 0 Type I The alkali metals column leXplode in cold water 0 Type II The alkali earths column 2 dissolve in hot water 0 Type III The transition metals dissolve in acid 0 Type IV The coinage metals don t do anything Not 100 accurate but good enough for an A alright a low A in CH301 Foreign Language Class Chemistry 506 All of you must have taken a foreign language at some time This means you ve had practice at memorizing large collections of random letters that make up the names we assign to different types of chemical compounds We are specifically interested in procedures for naming BINARY compounds which are formed by combining two elements and TERNARY compounds formed by putting together three elements To assist us in our endeavor it will be of great assistance to memorize the now expanded list of common cations and anions shown in the Table below Try putting these on ash cards as well Naming Binary Compounds Let s look at rules for BINARY IONIC COIVIPOUNDS In putting together two elements as ions the following rules apply Rule 1 The element that is more metallic more electronegative is listed first Example Sodium is always listed first because it is always l Rule 2 If the element has more than one common oxidation state that oxidation number is included in parenthesis after the element Copper is either Copper I if it is H oxidation state or Copper II if it is 2 oxidation state Rule 3 The element with less metallic character is listed second This second element is named by adding the suffix ide to the STEM of the element Naming the nonmetals element symbol stem name boron B bor boride carbon C carb carbide silicon Si silic silicide nitrogen N nitr nitride phosphorous P pho sph phosphide arsenic As arsen arsenide antimonv Sb antimon antimonide oxygen 0 ox oxide sulfur S sul sul de selenium Se selen selenide hydrogen H hydr hydride uorine F uor uoride chlorine Cl chlor chloride bromine Br brom bromide iodine I iod iodide Examples of Binary Compound Names Compound Name LiBr lithium bromide MgC12 magnesium chloride LiZS lithium sulfide A1203 aluminum oxide Na3P sodium pho sphide Mg3N2 magensium nitride Multiple Oxidation Numbers If only life were this simple Recall that not all elements have a single common oxidation number in ionic form The idea of using a Roman numeral after the name was proposed to name these compounds However there is an older way of naming these ambiguous compounds using ous and ic to terminate the metal The ic stood for the higher oxidation state and ous was attached to the metal with the lower oxidation number copper I is also called cuprous copper H is also called cupric Examples compound older name modern name FeBr2 ferrous bromide iron H bromide FeBr3 ferric bromide iron III bromide SnO stannic oxide tin H oxide Sn02 stannous oxide tin I oxide TiC12 titanium H chloride TiCl3 titanium III chloride TiCl4 titanium IV chloride Pseudo Binary Compounds Names Polyatomic Ions But what about all the compounds containing polyatomic anions and cations Ions like hydroxide OHquot ammonium NH4 sulfate 804392 Well these ions behave as simple monatomic anions and cations so we include them in our naming of binary ionic species using the same rules as above except that we have to memorize all of the polyatomic ion exceptions There are only 50 or 100 listed below for your memorization pleasure Common Cations Common Anions L1 1 lithium ion F 1 uoride ion Nal 1 sodium ion Clquot 1 chloride ion Kl 1 potassium ion Brquot 1 bromide ion NH4 1 ammonium ion 139 1 iodide ion Agl 1 silver ion OHquot 1 hydroxide ion C02 2 cobalt 11 ion CN39 1 cyanide ion Mg2 2 magnesium ion ClO39 1 hypochlorite Ca2 2 calcium ion C102quot 1 chlorite ion Ba2 2 barium ion C103quot 1 chlorate ion Cd2 2 cadmium ion C104quot 1 perchlorate Zn2 2 zinc ion CH3COO39 1 acetate ion Cu2 2 copper 11 ion MnO439 1 permanganate Hg22 2 mercury 1 ion N02quot 1 nitrite ion Hg2 2 mercury 11 ion N03quot 1 nitrate ion Mn2 2 manganese 11 ion SCN39 1 thiocyanate Ni2 2 nickel 11 ion 0239 2 oxide ion Pb2 2 leadH ion 8239 2 sulfide ion Sn2 2 tin 11 ion HSO339 1 bisulfite ion Fe2 2 iron 11 ion SO32quot 2 sulfite ion HSO439 1 bisulfate ion Fe3 3 iron 111 ion SO42quot 2 sulfate ion P043quot 3 phosphate ion Al3 3 aluminum ion HCO339 1 bicarbonate Cr3 3 chromium 111 ion C032quot 2 carbonate ion CrO4239 2 chromate ion Cr207239 2 dichromate ion Examples of compounds made with pseudobinary ion name sodium sulfate nitrate lithium ammonium chloride So What if it isn t an ion Naming Binary Molecules Covalent Bonds Often two nonmetals are put together In these cases neither has a great desire to rip away or give up electrons so ionic species aren t formed Moreover these types of compounds may exist in a variety of oxidation states Rather than deal with oxidation state the number of each atom is listed with a prefix noting the number of atoms of each element Iatoms 2 3 4 5 I6 7 I8 I I prefix I di I tri I tetra I penta I hexa I hepta I octa I Examples of molecules name carbon dioxide sulfur trioxide di uoride hexaoxide dichorine Ternary compounds after two comes three Ternary compounds contain combinations of atoms from three different elements Things can get really complicated with the additional element so we will stick to just a few simple classes First in working with ionic compounds there were a variety of polyatomic ions that you were asked to memorize These followed the basic rules of binary ions and are easy to name IF you have them all memorized Ternary Acids and Their Salts There are a collection of well know ternary acids which consist of hydrogen oxygen and a nonmetal The most famous example is H2804 sulfuric acid Rules for Naming Ternary Acids There are some basic rules for naming such compounds which depends upon the oxidation state of the central atom XXX Ternary acid anion salt decreasing perXXXic acid perXXXate decreasing oxidation XXXic XXXate oxygens number Of X XXXous acid XXXite on X hypoXXXous acid hypoXXXite Examples of Ternary Acids acid name sodium salt name HN02 nitrous acid NaN02 sodium nitrite HNO3 nitric acid NaNO3 sodium nitrate H2803 sulfurous acid NagsO3 sodium sulfite H2804 sulfuric acid NaZSO4 sodium sulfate HClO hypochloric acid NaClO sodium hypochlorite HC102 chlorous acid NaC102 sodium chlorite HClO3 chloric acid NaClO3 sodium chlorate HClO4 perchloric acid NaClO4 sodium perchlorate The end I have never done anything so boring in my life as type this particular set of notes
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