Exam 2 Study Guide
Exam 2 Study Guide CHE 106 - M001
Popular in General Chemistry Lecture I
CHE 106 - M001
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This 20 page Study Guide was uploaded by Madeline Merwin on Tuesday October 27, 2015. The Study Guide belongs to CHE 106 - M001 at Syracuse University taught by R. Doyle in Fall 2015. Since its upload, it has received 37 views. For similar materials see General Chemistry Lecture I in Chemistry at Syracuse University.
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Date Created: 10/27/15
Doyle Chemistry CHP 4 Exam two will have different exams all mixed up 4 levels of test bank questions all of the questions were level 2 questions except for 2 level 1 and 1 level 3 Exam 2 is much more difficult The homework question will be harder than the exam questions So get the 10 on the homework and it will help you test grades Easiest of the next 3 chapters 456 are all very different There is not relationship betweent hem Reactions in aqueous solution How is it that everything takes place in water The properties of water H2S stinking rotten gas small Chemical they should be the same not two different states and different anything else Water s partial charge what will dissolve in water and what won t What is a solution defined as homogeneous mixtures of two or more pure substance The solvent the substance in greatest abundance So water is the life Solutions 0 Solutions are defined as homogeneous mixtures of two or more substances 0 The solvent is present in greatest abundance 0 All other substances are solutes Ions in aqueous solutions 0 Ionic theory of solutions Many ionic compounds dissociate into independent ions when dissolved in water 0 The compounds that freely dissociate into independent ions in aqueous solution are called electrolytes 0 Their aqueous solutions are capable of conducting an electric current 0 When an ionic substance dissolves in water the solvent pulls the individual ions from the crystal and solvates them called dissociation 0 Water is great for this because while it is a neutral atom the slightly pos O and slightly neg H atoms break apart the ionic compounds 0 Some ionic compounds dissociate into ions and the resulting solution is electrically conducting so we say the molecular substance is an electrolyte 0 dissolve but do not dissociate into ions These compounds are referred to as nonelectrolytes Dey dissolve in water to give a nonconducting solution Glucose will dissolve in water 0 A nonelectrolyte may dissolve in water but it does not dissociate into ions when it does This yields a nonconducting sol 0 Molecular solids typical do not form electrolytes exceptions for acids HCl HNO3 0 Electrolytes are substances that dissolve in water to give an electrically conducting solution 0 Ionic solids that dissolve in water are electrolytes Most entirely dissolve completely into ions and are strong electrolytes 0 Molecular compounds such as acids also dissociate in aqeous solutions and are considered electrolytes 0 Solutions of weak electrolytes contain only a small percentage of ions We denote this by writing the equation with a double arrow In summary substances that dissolve in water are either electrolytes or nonelectrolytes Strong Electrolyte Weak Electrolyte Nonelectrolyte All strong Acids table 42 Weak acids and weak bases All other compounds ionic substances ionic substances molecular substances Form a strong conducting Form a weak conducting Form nonconducting solution because it is solution because it is solutions because they dissolved as ions dissolved as small amt of ions dissolve as molecules DEF DEF An electrolyte that eXists in An electrolyte that dissolves solution almost entirely as in water to give a relatively ions small percentage of ions Ionic Solids and Electrolytes Qs If you have equal concentrations of each of the following which will have the highest conductivityaka the greatest electrolyte ACaC12 Only 3 ions B KBr Only 2 ions CNe2SO4 Only 3 DAlNO33 only 4 E LiCH3OO only 4 All will dissolve and disassociatebreak apart into its ions in water The key is more ionsconductivity The answer is D the most ions the more current Strong Acids Strong Bases Hydrochloric HCl Group 1A metal hydroxides LiOH NaOH KOH RbOH CsOH Hydrobromic HBr Heavy group 2A metal hydroxides CaOH2 SrOH2 BaOHl2 Hydroiodic HI Chloric EClOg Perchloric HClO4 Nitric HNO3 Sulfuric H2504 Precipitation ruleswhat will dissolve in water and what will not What is weak and what is strongwho entirely gives e and who only partially does How many ions doe sit have which has the most Soluble Ionic Compounds Important Exceptions Compounds containing NOg None CH3CQCF None Cl Compounds of AgI Ilgfi and PbP Br Compounds of Pig Hgfi and Pb2 I Compounds of AgI Hgfi and Pb2 8042 Compounds of Sr2 Bazl Him and Pb Insoluble Ionic Compounds Important Exceptions Compounds containing 32 Compounds of NI lf the alkali metal cations and Ca2 5132 and B512 C0532 Cornpounds of N Hf and the alkali metal cations PC143 Compounds of NH4 and the alkali metal cations OH Compounds of the alkali metal cations and NHf Ca2 Sr2 and Ba2 2 things Solubility tables and the concept of strong and weak The in the middle is hybrid but it s weak Strong Electrolyte a strong electrolyte is one that eXists in solution almost entirely as ions Fully dissociates Most ionic solids are strong electrolytes Weak Electrolyte Dissolves in water but gives a relatively small percentage of ions To indicate this weak electrolyte situation we use the double arrow Weighted one way or the other which side is more molecular This indicates the equilibrium of both species Most Soluble molecular compounds are either nonelectrolytes or weak electrolytes In the molecular world they are either all molecular or not at all The exception are bases and acids Tables in the book will be good to memorize 41 42 These are rules you can learn and understand them or you can just learn them Solubility rules You must know whether it will dissolve for any of this stuff to matter and be relevant Substances vary widely in their solubility in water 0 Things that dissolve in olive oil are the best for anesthetics Anything that ends in the nitrate ANYTHING ending in ate dissolves in water no exception Most sulfites dissolve except for with heavy metals Sr Ba Hg Pbbottom right hand corner of the periodic table Barium can be ingested and them have you be xrayed to see if you have a blockage in your digestive tract Most ending with ide dissolve but no Ag Hg and Pb GO OVER THE INSOLUABLES SO writing molecular Reactants and products are written as if they were molecules even if they may exist in solutions as ions Ionic equations represent strong electrolytes as separate independent ions A complete ionic eqn is a chemical equation in which strong electrolytesex Soluble ionic compounds are written as separate ions Net ionic eqn eqn with spectator ions removed Spectator ions an ion in an ionic equation that des not take part in the reaction Write a molecular ionic equation from the other one Balance it from charge must have net neutrality Energy or matter cannot be created or destroyed l 2 A molecular equation is one in which the reactant and products are written as if they were molecules even though they may unlikely but may exist in solution as ions An ionic equation represents the strong electrolytes as separate independent ions a This is a more accurate representation of what is truly happening in solution You now know that when glucose goes in it doesn t come out the same and neither does NaCL and you show the big picture to gain better idea So what s going on In this reaction is calcium carbonate dissolves in water it precipitates down arrow our solution Number 2 is termed the complete ion equation a This is an equation that removes spectator ions b A spectator ion is one that Reaction types Oxidation reduction reaction always swapping ions Acid base reactions Precipitation reaction 0 Occurs in aqueous solution Because one product is insoluble O The precipitate is the insoluable said tp Metathesis exchange reaction means to transpose the ions in the reactant compounds exchange or transpose ions Precipitation Reactions A Acid Base rxs 3 Oxidation reactions 2 Acids and bases DEF The Archenius concept1884 defined and acid as a substance that produces hydrogen ion H when dissolved in water fare too loimiting Acids and bases are ELectrolates H e g HN03 Nitric Acid HN03water H aq N03 If you want the right order add acid to water The archenius concept defines bases as substances that produce hydroxide ions in water Eg Na0Hs waterNa aq 0HA aq Therefore Na0H is a base Eg NH3aq h2odouble arrowNH aq 0HA aq weak electrolyte hence the double arrow but is still a base 11 The Bronsted Lawry concept this says that an acid is a substance that transfers a proton to an acceptor which is the base 0 This says that acid bases rxns are actually proton transfer rxns Eg NH3aq h2o double arrow NH4 aq 0H aq NH3 accepts the proton so it s the base H20 donates the proton so it s the acid Eg HN03aq h2ol double arrow N03 aq H30aq HNOs donates the proton so it is the acid H20 accepts the proton so it s the acid Water is both an acid and a base depending on the circumstances H30hydronium ion DEF Neutralization reactions one of the chemical properties of acids and bases is that they neutralize each other DEF a reaction od an acid a base that produces a saltionic compound and water ABSalt H20 HCN KOH KCN H20 NET ionic equations result in a transfer of a proton HO COMPL IONIC EQN Haq CL aq Kaq 0HaqKaQ Cl aq H20l Net Haq 0Haq H20l AB rxns involving carbonate C02 Na2CO3aq2HClaQ 2NaCLaqh20C02 g Sulfites and sulfides Nazso3 2HC1 2NAC1 H20soz Nazs2HC1j NaClHZS LOOOK UP WHAT UP AND DOWN ARROWS LOOK LIKE 3 Oxidation reduction rxns the transfer of e Oxidation a loss of e Reduction a gain of e One always happens with the other You cannot have one without the other Eg Fes CuSO4aq I FeSOaq Cus Use the net ionic eqn to see what is happening subscripts Evolution of water and sky used to be green and once Oxygen evolved it all turned blue Oxidation numbers are a conceptual tool to track e in a reaction DEF The oxidation numberstate of an atom in a substance is the actual charge of the atom if ut exists as a monatomic ion Rules 1 A pure element has the ox of zero 2 Monoatomic ions have the ox is the charge of the ion 3 Oxygen ox is 2 w exception to H202 and other peroxides when ox l 4 Hydrogen ox 1 5 Halogens ox F is l in all of its compounds Other halogens are 1 unless the other element is another halogen or oxygen 6 Compounds and ions the sum of the ox of the atoms in a compound is zero The sum in polyatomic ion equals the charge on the ion Lets look at the ion reaction eqn Can break the net ionic equation down even further Half reaction one of the two parts of an oxidation reduction reaction One involves the loss of electrons oxidations and the other involves the gain of electronsreductions M01 eqnleomplete eanINet eqnl ox red rxn Half reaction eqn Note the species that was oxidized caused our reduction and is therefore called our reducing agents IT itself is oxidized When you displace an element during a reaction like this this is called a displacement reaction Displacement Oxidation reduction eqn Balancing Ox Re Rxns 0 An oxidizing agent is a species that oxidizes another species it is itself reduced 0 A reducing agent is a species that reduces another species it is itself oxidized Zns 2HClaq a ZnCl2 aq H2 g Oxidation numbers Zn 0 gt Zn 2 Zinc is oxidized H 1 gt H 0 Hydrogen is reduced But now we deal with charges Mass must be balanced but also much change Use the half rxn to help Most of the reactions we have discussed occurred in a solutions so when you run reactions in liquid it is convenient to dispense volumes DEF Concentration is the quantity of solute in a standard quantity of solution DEF Molar Concentration molarity is the moles of solute in l L of solution The reason we define it to liter is bc we use mL Molarity Moles of solutel of solutions Moles per liter H20 in one mol has 602 1023 moleculesl8g so 1M of H20 l8g in L Eg A sample of 00341 mol ironIII chloride FeCl3 was dissolved in water to give 250 mL of solution What is the molarity of the solution M 00341 mole of FeCl3 136MFeCl3 00250 hter of solutlon NOTE Molarity and Volume are inversely proportional This takes the form of Mi x ViMf x Vf Iinitial Ffinal Adding to the intial volume to increase production of Vf leads to a dec of Mf Eg H2SO4 aq2NaOHaq I 2H20l Na2SO4aq Suppose a beaker contained 35 0 mL 0175 M H2804 1 First we must convert the 00350 L 350 mL to moles of H2804 using the molarity of the H2804 2 Then convert to moles of NaOH from the balanced chemical equation 3 Finally convert to volume of NaOH solution using the molarity of Na0H Chapter 5 Thermodynamics Theremoheat dynamicsmovement Heat ow amics The science of the relationship between heat and energy 0 Thermochemistry is the study of the quantity of heat absorbed or evolved by chemical reactions The Laws of thermodynamicsZeroth You must play the game First You can39t win 8econd You can39t break even Third You can39t quit the game lSt aka Law of Conservation of Energy states that energy cannot be created or destroyed in a chemical reaction 2nd he second law of thermodynamics states that the entropy of any isolated system not in thermal equilibrium almost always increases 3 The third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches absolute zero If you obtain absolute zero you can stop absolute chaos but that is unattainable SIDE NOTE Gibbs free energy The energy associated with a chemical reaction that can be used to do work The free energy of a system is the sum of its enthalpy H plus the product of the temperature Kelvin and the entropy 8 of the system G2H TS Free energy of reaction 5 G The change in the enthalpy 5 H of the system minus the product of the temperature Kelvin and the change in the entropy 5 8 of the system G H T S Thermochemistry is the study of the quantity of heat absorbed or evolved by chemical reaction Enthalpy is a state function depends on how much is there Energy is the ability to move matter or to do work The ability to do stuff It can be many forms matter is a form of energy 1 Radiant energy eX inerfed electromagnetic radioation 2 Thermal energy Essential the motion of molecules or atoms 3 Chemical the energy stored in bonds For humans we store this as ATP I wonder what dinosaur cells looked like There are 3 overall broad concepts of Energy 1 Kinetic energy the energy associated with an object by virtue of its motion 2 Potential Energythe energy an object has by virtue of its position in a field of force EX Humans and gravity 3 Internal Ethe sum of the kinetic and potential energies of particles of a substance Win a substance there is energies in the particles that make up the substance 1 Kinetic E an object of mass m and speed or velocity v have energy Ek This shows that the kinetic E of an object depends on both its mass and its speed EXam Q consider the kinetic E of a person of mass 130 lbs 59 kg traveling in a car at 60 mph 268 ms Ek 1259o kgX288 ms 2 Ek2l2X10 A4 kg X msquot2aka a Joule 6184 Jl calories 1 cal4184 J 2 Poential Energy the E depending on the virtue of the position in an applied field of force EX Water in a damn of mass m has a position h in a gravitational field g of Epmgh Simple use of your brain to get EX What is the Ep of 1000 lb of water at the top of a 300 ft dam 4536 kg X 980 msA2 X 9144 m Ep406 X 10 A5 kg X mA2sA2 or 406 X 105 J Energy can be converted but never destroyed it is conserved lSt thermodynamics law NOTE that books use Etotal but in this class we use U U is the energy of the particles making up a substance So the total energy Law of conservation of Energy which states that energy may be conserved into one form or the other but the total quantity of EnergyEt0mremains constant A same as the first law of thermodynamics Heat of Reaction Heat is as the energy that ows into or out of a system because of the difference in temperature between the system and its surroundings Heat and temp are not the same Heat has a mass component temp does not Heat ows from a region of higher temperature to one of lower temperature once the temperatures are equal heat ow stops and thermal equilibrium is reached It aaaall boils down to the universe trying to reach thermal equilibrium to share the energy in essence Heat itself is denoted at q If q is heat is absorbed by the system Endothermic reaction Heat into a system If q is heat is evolved from the system Exothermic reaction Heat out of a system The heat of reaction is the value of q required to return a system to its original temperature after a reaction How much energy would be required to take you up and pick you up off the ground once you ve jumped and hit the bottom We look at it this way so we are able to physically measure it We grasp it from back to front View is from equilibrated hot cup of coffee to hot cup of coffee Based on scientists ability to perform and experiment Enthalpy and its change The heat absorbed or evolved depends on the conditions in which it occurs Usually a reaction occurs in an open vessel at atmospheric pressure If you change pressure you will change the protein The heat of this type of rxn is denoted by qp heat at constant pressure You have to denote the pressure bc it plays a major fole on Q and energy ow TO obtain the heat absorbed or eveolved in a chemical rexm you use extensive properties Enthalpy aka H is a state function An extensive property of a substance that can be used to obtin the heat absorbed or evolved in a chemical rxn An extensive property is one that depends on the quantity of substance mass volume a state function is a property of the system that depends only on its present state and so is independent on any previous history Enthalpy The change in enthalpy AH Deltachange triangle You don t actually measure H you only measure the change in H Because this is thermoDYNAMICS energy is changing movement The change in enthalpy for a rxn at a given temp and pressure which is called the enthalpy of rxn is obtained by subtracting the enthalpy of the reactants from the enthalpy of the products AHH H products reactants EX A neg delta H 3686 This means that 3686 is released This represents the entire change in internal energy IIJ minus any expansion work done by AH qp the system Enthalpy and internal Energy U is defined as the heat at constant pressure qp plus the workw done by the system U qp w W the change in vol at a given pressure AU AH PAV This means that internal EU changes by energy entering or leaving 1H or the system increase or decreases in volume PIN A thermochemical equation is the chemical equation for a reaction including phase labels in which the equation is given a molar interpretation and the enthalpy of reaction for these molar N2g3H2g a 2NH38 AH 918 M amounts is written directly after the equation Ex It s important to note phase labels because the enthalpy change DH depends on the phase of the substances Doyle The end justifies the means How you got to where you re at is irrelevant it only matters that you got there Enthalpy of Reaction Heat of Rxn The Change in enthalpy A H is the enthalpy of that products minus the enthalpy of the reactants Also the value of q requited to return a system to the original temperature at the completion of a reaction A H Hproducts Hreactants Combustion gives off heat exothermic and neg enthalpy it takes that much heat to get it back AH lt0 is exothermic PAY ATTENTION TO SIGNS IN CHP 5 These enthalpies are in k unless they are in relation to moles and then it is kJmol Hesse s law is dependent on the idea of a state function Thermal chemical eqn 1 The eqn is given a molar interpretation aka BALANCE 2 The enthalpy of the an is written after the equation 3 The phase labels must be included BC remember H is a state function so phase is important 4 When multiplying by any factor the value of A H for the new equation is obtained by multiplying by the same factor BC remember H is an extensive property 5 When a Chemical eqn is reversed the sign of A H is reversed Sign is important In other words the reverse an is equal in magnitude but opposite in heat ow terms EXAM q How much heat q is obtained by burning 10g of CH4 in 02 Fill in CH4 g 202 g a C02 g 2H20l 1 Balanced the eqn 2 Second mole conversion X lOgl6gpermol0625 3 Conversion factor mol to kL using enthalpy of an One mole 8903 k 4 Answer 0625 mol 556kj Heat capacity determines the amount of heat a material can absorb C or the heat required to raise the temp of a substance How do you relate the different heat materials to each other I We use specific heat capacity Specific heat capacity specific heat the heat required to raise the temperature of one gram of a substance by one degree Celsius To obtain multiply the specific heat of the substance s times its mass in grams m and the temperature change AT Cs Qs X m X A T Different substances have different Cs values you can generate tables of them and measure their heat capacities Water s is always 4184 jg K which is also 1 calorie1 cal Elements and molecules are in joules grams per K Qs Cs X m X A T Calculate the heat absorbed when the temperature of 15 g of water is raised from 20 degrees centigrade to 50 degrees Q 4l8Jg C150 g 30 C 188 X 108 J To physically measure heat absorbed or energy use the calorimeter9 a device used to measue the heat absorbed or evolved during a physical or chemical change Its content is the negative of the qwlulilucm nu heat of the reaction in this specific eXample Hesse s Law of heat summation states that for a chemical equation that can be written as the sum of multiple reactions or steps2 or more the enthalpy change for the overall is the sum of the A Henthalpy for each step eXplains why A H a state function There is no history how you got there in terms of the chemical eqn is irrelevant Hesse s law is very helpful when you can t measure reaction energy change directly because over the years we have built up tables of enthalpy s reaction 2 important rules for manipulating thermochemical eqns 1 When a thermochem eqn is multiplied by any factor the value of AH for the new eqn is obtained by multiplying the AH in the orig eqn by the same factor 2 When a chem eqn is reversed the value of AH is reversed in sign 3 To find the enthalpy in these two reactions we multiply the first equation by 2 and reverse the second equation They will sum together to become the third 35ls2 31gjl gt 2504 AHquot I297 ijllxiiijll L I w Llljs39IlClI gl 43933432 AHquot 198 klegtltIj 1 It 238 302g a 2303 g AHO 792 k The term standard state refers to the standard thermodynamic conditions to chose for substances when comparing or listing thermos data 1 atmosphere pressure and the specified temp usually 25 C TO define AV as standard we use A H f naught is the enthalpy change for the formation of one mole of a substance and its standard state from its elements in their standard AH change for a rxn in which reactants are in their standard statesAHO AH zero or AH naught for a pure element at 25 degree C lAPM is zero The standard of enthalpy of formation of a substance denoted AHfO is the enthalpy change for the formation of one mole of a substance in its standard state from its component elements in their standard state 0 Consider water formation the most stable forms of Hydrogen and oxygen at 1 ATM and 25 deg are H2g and O2g H2g02g gt HZOZAH 2858kJ 0 The thermal equation is If we look at the AHfO the book gives ton of different values for different number depending in stateg l aq s but also diamond or graphite these are allotropes the property of some chemical elements to eXist in two or more different forms in the same physical state so be careful Phase matters Use law of summation of heats of formation the enthalpy of a reaction is equal to the total formation energy of the products minus that of the reactants AH 0 Z nAH products Z mAH reactants AHfO 2 means Sum of m and n are the coefficients of the substances in the chem equation EX You record the values of AHfO under the formulas in the equation multiplying them by the coefficients in the equation 4NH3 g 502 g a 4N0g 6H20g 4 45 9 50 4903 6 2418 You can calculate AH0 by subtracting the values for the reactants from the values for the products Using the summation law AH 0 Z nAHJ Z products Z mAHJ Z reactants AH0 4903 6 2418 kJ 4 45 9 50 kJ AHO 906 kJ 4NH3 g 502g a 4N0g 6H20g 0 Answer Heat of Vaporization use standard enthalpies of formation calculate the heat of vaporization AHovap 0 1X 2858 1X 2418 H200 gt H20g AH 3 Z nAHJ Z products Z mAHJ Z reactants 0 44 kJ CHP 6 Electron Configurations should be very well understood Exam 2 is on Chp 456 held next Thursday October 29th This chp is science fictiony E comes in many formsATP Thermal and now radian EDLight is electromagnetic Energy is the capacity to move matter It comes in many forms 0 Radiant Energy Electromagnetic radiation 0 Thermal Energy Associated with random motion of a molecule or atom 0 Chemical Energy Energy stored within the structural limits of a molecule or atom Emission Line Spectra of Some Elements spectra plural of spectrum are due to light and matter interacting A wave is a continuously repeating change or oscillation in matter or in a physical field 0 Light has a wave characteristic 0 It consists of oscillations in electric and magnetic fields that travel through space Visible light X rays and radio waves are all forms of electromagnetic radiation So the in the wave nature of light a wave can be characterized by wavelength and frequency The wavelength A lambda is the distance between any two adjacent identical points of a wave The frequency nu of a wave is the number of wavelengths that pass a fixed point in one second Measured in HzHertzsA lwaves per second The speed of the wave on ms is expressed by multiplying the freq v wavessec and the wavelength A mwaves of a light wave 0 In a vacuum the speed of light is c299979245 8 ms approx 30xlOA8 mS MEMORIZE this is a constant value for all A and v 0 SO cv A and this equation is true for all forms of electromagnetic radiation The range of the A or v of electromagnetic radiation is called the electromagnetic EM spectrum Visible light extends from the violet end of the spectrum at about 400 nm to the red with wavelengths about 800 nm Beyond these extreme EM radiations are not visible to human eyes What is the wavelength of a yellow light with a freq of 509 x 10A14 sA l 0 If cv A the rearrange the eqn to Acv and plug in values 0 V 509 x lOAl4 sA l c300x10 8 msspeed of light A 0 Answ 589 x lOA 7 m or 598 nm Quantum effects and photons background end of 19th century wave theory seemed to explain all experimental observations except for colored metal ames considering light as just waves So Einstein proposed that light had both wave and particle properties ie photoelectric effect experiment based on work of Max Planck 0 Planck atoms of a solid oscillate with a definite v An atom could only have energie of vibration E Enhv O V frequency ninteger h Planck s constant of 663xlOA 34 st 0 Thus the only energies a vibrating atom can have are lhc 2hv 3hv and so on 0 Numbers symbolized y n are quantum numbers the vibrational energies of the atoms are said to be quantized I Energy is changeable in a uniform continuous way but at the atomic level it is quantized meaning that energy can only be changed in discrete incrementseX Walking up stairs 0 Einstein extends this to include the structure of light used this concept to eXplain photoelectric effect 0 If a vibrating atom changed energy from 3hv to 2hv I it would decrease in energy by hv O This energy would be emitted as a bit or quantum of light energy 0 Thus light consists of quanta called photons or particles of EM energy 0 This energy is proportional to the observed frequency and the proportionality constant would be Planck s h I E hv O Einstein s assumption that an electron is ejected when struck by a Single photon suggests that it behaves like a particle Photoelectric effect is the ejection of electrons from the surface of a metal when light shines on it 0 When the photon hits the metal its energy hv is taken on by the electron 0 After the photon ceases to eXist as a particle it is absorbed Electrons are ejected only of the light exceeds a certain threshold frequency EX Violet light will cause potassium to eject electrons but no amount of red lightlower freq has any effect on K Wave Particle duality of light the wave and the particle pictures of light should be regarded as complementary views of the same physical entity 0 E hv displays this duality E is the energy of the particle photon and v is the frequency of the associated wave 0 EX What is the energy of a photon corresponding to radio waves of frequency 1255 X 106 sA l O Solve for E using Ehv 6626 X IDA 34 JXs X 1255 X 106 squot 183156 X IDA 28 J PRIOR to Bohrs work the stability of the atom couldt be eXplained using the then current theories Then in 1913 using Einstein and Planck work he applied a new theory to the simplest atom hydrogen But first the Atomic Line structure 0 When a heated metal filament light bulb emits light we can use a prism to spread out the light to give a continuous spectrum that is a spectrum containing light of all wavelengths 0 The light emitted by a heated gas such as hydrogen results in a line spectrum a Spectrum Showing only Specific wavelengths of light 0 For atoms amp molecules only a line spectrum of discrete wavelengths can be observed not a continuous spectrum such as from a white light source SO Bohr s Theory of the Hydrogen Atom His Postulate s Bohr set down postulates to account for l the stability of the H atom and 2 the line spectrum of the atom 1 Energy level postulate An electron can have only specific energy levels in an atom quantized 2 Transitions between energy levels An electron in an atom can change energy levels by undergoing a transition from one energy level to another He thus derived the formula E R g nl23cgto forHatom n 11 principle quantum number RhRydberg Constant J of 218 X 10 18 J for the energy levels of the electron in the hydrogen atom When an electron undergoes a transition from a higher energy level to a lower one the energy emitted as a photon i R11 0 From Postulate 1 Hi f iinitial ffinal Energy of emitted photon hv 2 AE 2 EJ El 0 If we make a substitution into the previous equation that states the energy of the emitted photon hv equals Efinal minus Eintial 1 1 rearrange to get n2 n2 f l l 1 Energy of the emitted photon hv Rh 0 800000 therefore Bohr s Postulates cont Bohr s theories eXplain both the emission and the absorption of light When and e falls aka energy decreases from n3 to n2 energy level a photon of red light A 685 nm is emitted When a red light of this same A shines on a hydrogen atom in the n2 level the energy is gained by the electron that undergoes a transition to n3 EX Calculate the energy of a photon of light emitted from a hydrogen atom when an electron falls from level n 3 to level n 1 EhvRh12 12 E 2 18 1018 1 1 nr 111 X J 17 272 E 194 XIOA18 J Please note that AE final sign is negative because Energy is emitted when the e drops from a higher to lower level Bohr s theory established the concept of atomic energy levels however he didn t fully explain the wave like e behavior Current ideas about atomic structure depend on the principles of quantum mechanics a theory that applies to subatomic particles such as e Louis de Broglie said if light has particle aspects then perhaps these particles of matter have wave characteristics A particle w mass m and a velocity v has an associated 2x A hmv is the de Broglie relation h is Planck s constant Then why are the wave properties not commonly observed The de Broglie relation shows that a baseball 0145 kg moving at about 60 mph 27 A 663x10 34 kg mz 17gtlt1034m 0145kg27ms ms has a wavelength of about 17 X 103934 m Because as the answer shows the value is too small to be detected So electrons 0 Electrons are very light particles 91X10 31 kg 0 Electrons have wavelengths on the order of a few picometers 1 pm 10 12 m 0 Under the proper circumstances the wave character of electrons should be observable 1927 it was demonstrated that just like a X rays a beam of electrons could be diffracted by a crystal I leading to the electron microscope in 1933 QUANTUM MECHANICS The branch of physics that mathematically describes subatomic particles wave properties This eliminates the idea that an e has a precise orbit in an atom because this would be knowing its exact position and velocity but Heisenberg showed via quantum physics that you cannot possibly show both at the same time Buuuut we can obtain the probability of an e s location at a given point around the nucleus 0 Schrodinger defined this probability in a math eXpression called a wave function denoted by w psi 0 The probability of finding a particle in a region of space wz So wat are these wave functions called Atomic Orbitals I these describe the region of space where there is a high probability of finding electrons They have special sizes orientations and shapesin a 3 D space According to quantum mechanics each electron is described by four quantum numbers Principal quantum number 11 Size Magnetic quantum number m Orientation Angular momentum quantum number 1 Shape Spin quantum number ms The first three define the wave function in space for a particular electron The fourth quantum number refers to the magnetic property of electrons No two e can have the same 4 quantum numbers Impossible The shell number in which the e resides is represented by the quantum number n n1 2 3 n is related to orbital size The smaller 11 is the smaller the orbital The smaller 11 is the lower the energy of the electron For simple atoms such as H U or He n is the only quantum number determining the energy of the electron The angular momentum quantum l distinguishes the subshells within a given shell that have diff shapes Ea main shell is divided into subshells win each shell of quantum number 11 there are 11 sub shells ea w distinctive shapes l distinguishes them with any integer value from to 11 minus 1 The different subshells are denoted by letters Letter s p d f g l O l 2 3 4 The magnetic quantum number m distinguishes orbitals within a given subshell that have different shapes and orientations in space Each subshell is subdivided into orbitals each capable of holding a pair of electrons m can have any integer value from l to 1 Each orbital within a given subshell has the same energy The spin quantum number ms refers to the two possible spin orientations of the electrons residing within a given orbital Each orbital can hold only two electrons whose spins must oppose one another The possible values of mS are 12 and 12 To describe the orbitals we use the calculated probabilities of electron position s subshell orbital there is only one is spherical 0 Value of l is O O Spherical O Raduis od sphere increases with the value of n p subshell orbitals there are three are dumbbell shaped 0 Value of l is l 0 Have 2 lobes with a node between themdumbbell shaped or symmetrical bowling pin d subshell orbitals there are five are a miX of cloverleaf and dumbbell shapes 0 Value ofl is 2 m 2 1012 0 Mix of cloverleaf shapes and dumbbell shapes 0 Four of the five d orbitals have 4 lobes the other resembles a p orbital with a doughnut around the center EXAM OCTOBER 27 2015
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