The EASY Guide to Ace General Chemistry I and II: General Chemistry Study Guide, General Chemistry

ACEGENERALCHEMISTRYIANDII(THEEASYGUIDETOACEGENERALCHEMISTRYIANDII)BY:DR.

HOLDENHEMSWORTH

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TABLEOFCONTENTS

CHAPTER1:IntroductiontoChemistry

CHAPTER2:ComponentsofMatter

CHAPTER3:StoichiometryofFormulasandEquations

CHAPTER4:ChemicalReactions

CHAPTER5:QuantumTheoryandAtomicStructure

CHAPTER6:ElectronConfigurationandPeriodicProperties

CHAPTER7:ChemicalBonding

CHAPTER8:GeometryofMolecules

CHAPTER9:BondingTheories

CHAPTER10:GasesandGasLaws

CHAPTER11:Thermochemistry

CHAPTER12:Solutions

CHAPTER13:ChemicalKinetics

CHAPTER14:ChemicalEquilibrium

CHAPTER15:AcidBaseEquilibrium

CHAPTER16:SolubilityEquilibrium

CHAPTER17:Electrochemistry

CHAPTER18:NuclearChemistry

CHAPTER1–INTRODUCTIONTOCHEMISTRY

WhatisChemistry?

Chemistryisthebranchofscienceconcernedwiththeunderstandingofmatter;thesubstancesitiscomposedofandtheirproperties,aswellasthewaysinwhichtheyinteractandchangetoformnewsubstances.

Matter

Matterisanythingthathasmassandtakesupspace.Massistheamountofmatteranobjectcontains;awayofquantifyingmatter.Matterexistsinthreephysicalstates.

Solid–matterwithfixedshapeandvolume(rigid)

Liquid–matterwithafixedvolumebutindefiniteshape

Takesontheshapeofthecontaineritisin

Gas–matterwithoutafixedshapeorvolume

Conformstothevolumeandshapeofitscontainer

PhysicalandChemicalProperties

Physicalproperty–characteristicsthatcanbemeasuredandobservedwithoutchangingthechemicalmakeupofthesubstance

Examples:color,meltingpoint,boilingpoint,density,etc.

Physicalchange–asubstancechangesitsphysicalappearancebutdoesnotchangeidentity

Changesinstate(e.g.,liquidtogas,solidtoliquid)areallphysicalchanges

Chemicalproperty–anypropertythatbecomesevidentduringachemicalreaction

Examples:pH,corrosiveness,etc.

Chemicalchange(akachemicalreactions)–asubstanceistransformedintoachemicallydifferentsubstance

Mixtures

Mixturesarecombinationsoftwoormoresubstancesinwhicheachsubstancekeepsitschemicalidentity.Mixturescanbeseparatedintotwoormoresubstances.

Heterogenousmixtures–mixturethatisdividedintodifferentregionsofappearanceandproperties

Resultsfromcomponentsnotbeingdistributeduniformly

Homogenousmixtures–mixturethatisuniformthroughoutwithoutanyvisibleseparations

Solutionsarehomogenousmixtures

Whereasolid(thesolute)isdissolvedinaliquid(thesolvent)

ElementsandCompounds

Puresubstanceshavedefiniteandconsistentcompositionandarecomposedofelementsorcompounds.

Element-substancethatcan’tbebrokendownintoothersubstancesbychemicalmeans

Compound–substanceformedfromtwoormorechemicalelementsthatarechemicallybondedtogether

Lawofdefiniteproportions

Purecompoundsalwayscontainexactlythesameproportionsofelementsbymass

Energy

Energyisthecapacitytodowok.

Kineticenergy–energypossessedbyanobjectduetoitsmotion

Potentialenergy–energystoredinmatterbecauseofitspositionorlocation

Somethingsuspendedintheairhashigherpotentialenergythansomethingsittingontheground

TotalEnergy=potentialenergy+kineticenergy

Lowerenergystatesaremorestableinnature

Lawofconservationofenergy

Energycan’tbecreatedordestroyed…butitcanbetransformed

Example:potentialenergycanbeconvertedtokineticenergy

Energyisalwaysconserved

ScientificMethod

Thescientificmethodisatechniqueforinvestigationthatisusedtoanswerscientificquestions.

Hypothesis-aproposedexplanationmadeonobservationsorlimitedevidencethatservesasthestartingpointforfurtherinvestigation

Theory–explanationofgeneralprinciplesofaphenomenathathasbeenrepeatedlytestedandobserved

Fact–indisputabletruth

Stepsinscientificapproach

Observations,Hypothesis,Experiment,Developmentofamodelortheory,Furtherexperimentation

MeasurementsMeasuredquantitiesconsistofanumberandaunit.

UnitsarestandardizedintheformoftheInternationalSystemcalledSIunitsUnitshaveassociatedprefixestomakethemeasiertouseandreports

Conversionfactors–amathematicalmultiplierusedtoconvertaquantityexpressedinonesetofunitsintoanequivalentquantityexpressedin

Example:1yard=3feet(10yard=30feet)ScientificNotation

ScientificnotationisawayofhandlingverylargeorverysmallnumbersScientificnotationforanumberonlycontainssignificantfigures

Examples525,000=5.25x105

2,301,000,000=2.301x109

0.000000000670=6.70x10-10

Considerthefollowing:0.000023=2.3x10-5

Theexponenton10isthenumberofplacesthedecimalpointmustbeshiftedtogivethenumberinitslongform

Positiveexponent,shiftthedecimalpointtotherightNegativeexponent,shiftthedecimalpointtothe

leftSignificantFigures

Allnon-zeronumbersarealwayssignificant

1,2,3,4,5,6,7,8,and9Zeroesinbetweennon-zeronumbersarealwayssignificant

10001–5sigfigsAfinalzeroortrailingzeroesinthedecimalportionaresignificant

0.00500–3sigfigs1255.0–5sigfigs

Allzeroestotheleftofadecimalpointandthataddvaluetoanumberaresignificant

100.0–4sigfigs0.1–1sigfig

Inthiscase,thezeroaddsnovalue;itistheretoavoidconfusionandbyconvention

ExactNumber

Exactnumbersareconsideredtohaveaninfinitenumberofsignificantfigures

TheydonotaffectaccuracyorprecisionofanexpressiontheyareinYoudonothavetoconsiderthesignificantfiguresinexactnumberswhendoingcalculations

Conversionfactorsareexactnumbers

1yard=3feet(thereareexactly3feetinayard)1foot=12inches(thereareexactly12inchesinafoot)

MultiplicationandDivisionSignificantFigures

Firstperformalloperationsandarriveatananswer

Theanswershouldhavethesamenumberofsignificantfiguresasthenumberwiththeleastamountofsignificantfiguresusedinthecalculations

AdditionandSubtractionSignificantFigures

FirstperformalloperationsandarriveatananswerInadditionandsubtractionyouonlyhavetoconsiderthesignificantfiguresinthedecimalportion

Theanswershouldcontainnomoredecimalplacesthanthenumberwiththeleastamountofdigitsinthedecimalportion

Multiplication/DivisionCombinedwithAddition/Subtraction

FolloworderofoperationsIfthenextoperationtobeperformedisinthesamegroupasthepreviousoperationthendon’troundthecalculation

Forexamplewhenyouperformdivisionandthenmultiplication,youwouldnotroundthecalculation

Ifthenextoperationtobeperformedisintheothergroupfromthepreviousoperationthenyouwouldroundtheanswerusingtherulesbeforemovingontothenextoperation

Example:Youperformdivisionandthenextoperationissubtraction

Youwouldfirstroundtheresultofthedivisionusingthesignificantfigurerulesfordivisionbeforeyouperformsubtraction

AccuracyandPrecision

Accuracy–howclosearesultistotherealvalue

Precision–howcloserepeatedmeasurementsareinrelationtooneanother

Accuracyvs.Precision:

Uncertainty

Uncertainty–errorinameasurementExpressedasastandarddeviation

Whenmakingameasurementinvolvinganinstrument,themeasurementismadewithoneuncertaindigit

Example:Youmightrecordthemeasurementas20.03The3isanuncertaindigitbecauseitisestimatedandcan’tbereadoffexactlyfromtheinstrument

Temperature

Temperatureiscommonlyquantifiedusingthethreeunits:kelvin,Celsius,andFahrenheit.

Kelvin(K)–“absolutetemperaturescale”

Startsatabsolutezero

Containsonlypositivevalues

Celsius(˚C)–“waterbasedscale”

0˚C–freezingpointofwater

100˚C–boilingpointofwater

Mostcommonlyusedscalearoundtheworld

Fahrenheit(˚F)–“mercurybasedscale”

CommonlyusedintheUS

ConvertingTemperatures

FormulaforKelvintoFahrenheit:(9/5)(K-273)+32

FormulaforKelvintoCelsius:K–273

FormulaforCelsiustoKelvin:˚C+273

FormulaforCelsiustoFahrenheit:˚Cx(9/5)+32

FormulaforFahrenheittoKelvin:(5/9)(˚F–32)+273

FormulaforFahrenheittoCelsius:(5/9)(˚F-32)

CHAPTER2–COMPONENTSOFMATTER

ComponentsofMatter(Definitions)

Element-substancethatcan’tbebrokendownintoothersubstancesbychemicalmeans

Molecule-acombinationoftwoormoreatoms

Compound–substanceformedfromtwoormorechemicalelementsthatarechemicallybondedtogether

Mixture-twoormoreelements(orcompounds)minglingwithoutanychemicalbonding

LawsofMatter

LawofMassConservation

Totalmassesofsubstancesinvolvedinachemicalreactiondonotchange

Numberofsubstancesandtheirpropertiescanchange

LawofDefiniteProportions:

Purecompoundscontainexactlythesameproportionsofelementsbymass

LawofMultipleProportions

Iftwoelementsreacttoformmorethanonecompound,thentheratiosofthemassesofthesecondelementwhichcombinewithafixedmassofthefirstelementwillbeinratiosofsmallwholenumbers

PostulatesofDalton’sAtomicTheory

Allmatterconsistsofextremelysmallparticlescalledatoms

Allatomsofanelementareidentical

Theyaredifferentfromatomsofanyotherelement

Includinginmassandotherproperties

Atomsofanelementcan’tbeconvertedintoatomsofanotherelement

Compoundsresultwhenatomsofmorethanoneelementcombine

Agivencompoundhasaspecificratioofatomsofdifferentelements

PeriodicTableofElements

Theperiodictableisanarrangementofelementsinrowsandcolumnsbasedontheiratomicnumber,electronconfigurations,andchemicalproperties.

Period–horizontalrowonthetable

Group(Family)–columnonthetable

Elementsontheperiodictablecanbeclassifiedasmetals,nonmetals,andmetalloids

Metal–substancesthathaveluster,highheatconductivity,highelectricalconductivity,andaresolidatroomtemperature(exception:mercury)

Nonmetal–substancewithoutanymetalcharacteristics

Metalloid–substancethathavebothmetalandnonmetalcharacteristics

Atoms

Anatomisthesmallestunitofmatter.Atomsinteracttoformmolecules.Atomsarecomposedofsubatomicparticles(electrons,protons,andneutrons).

Electrons–negativelychargedparticles

Carriesachargeof-1.602x10-19Coulombs(C)

Chargeofatomicandsubatomicparticlesaretypicallydescribedasamultipleofthisvalue

So,referredtoas-1

Mass=9.10938291x10-31kg

Protons–positivelychargedparticles

Carriesachargeof+1.602x10-19Coulombs(C)

Referredtoasa+1electroncharge

Mass=1.67262178x10-27kg

Neutrons–unchargedparticles

Electricallyneutral

Mass=1.674927351x10-27kg

Protonsandneutronsarefoundinthenucleus

Nucleusisthecentralcoreofanatom

Electronsorbitthenucleusinan“electroncloud”

Elemental(atomic)symbol:shorthandrepresentationofatomsofdifferentelements

ExampleofanElementonthePeriodicTable:

Atomicnumber-numberofprotonsinanatomofaparticularelement

Foraneutralatom,numberofelectrons=numberofprotons

Allatomsofanelementhavethesameatomicnumber(samenumberofprotons)

Massnumber=thenumberofprotons+thenumberofneutrons

Allatomsofanelementsdon’thavethesamenumberofneutrons

Atomicweight(relativeatomicmass)–averagemassofatomsofanelement

Calculatedbasedontherelativeabundanceofisotopesinthatparticularelement

Units:atomicmassunits(amu)

Isotopes–atomsofanelementwiththesamenumberofprotonsbutwithadifferentnumberofneutrons

Sameatomicmassbutdifferentmassnumber

TypesofChemicalFormulas

Chemicalformulasareawayofexpressinginformationabouttheproportionsofatomsthatconstituteacompoundusing:elementsymbols,numericalsubscripts,andothersymbols(e.g.,parentheses,dashes).

Empiricalformula–smallestwholenumberratioofnumbersoftheatomsinamolecule

Molecularformula–actualnumberofatomsinamolecule

Structuralformula–chemicalformulashowinghowatomsarebondedtogetherinamolecule

CovalentandIonicBondsCovalentBonds

Twoatomssharetheirvalenceelectrons(electronsintheoutershellofanatom)

TwoTypes

Non-polarcovalentbond–electronssharedequallybetweenatoms

Electronegativityofthetwoatomsisaboutthesame

Typicallyelectronegativitydifferencebetweenthetwoatomshastobelessthan0.5fornon-polarbonds

Electronegativity–anatom’sabilitytoattractandholdontoelectrons,representedbyanumber

Polarcovalentbonds–electronsshareddisproportionatelybetweenatoms

Electronegativitybetweenthetwoatomsisdifferentbyagreaterdegreethan0.5butlessthan2.0

IonicBonds

Electronsaretransferred,notsharedbetweenatoms

Anatomwithhighelectronegativitywilltakeanelectronfromanatomwithlowelectronegativity

Typically,differenceinelectronegativityismorethan2.0

Ions

Ionsarechargedatomsormolecules.Ionsareformedwhenatomsorgroupsofatomsgainorlosevalenceelectrons.

Monatomicion–singleatomwithmoreorlesselectronsthanthenumberofelectronsintheatom’sneutralstate

Polyatomicions–groupofatomswithexcessordeficientnumberofelectrons

Anion–negativelychargedion

Cation–positivelychargedion

Ioniccompounds–associationofacationandananion

Thecationisalwaysnamedfirst

NomenclatureRulesforChargesonMonoatomicIons

Elementsingroup1formmonoatomicionswithchargesequaltotheirgroupnumber

Naisagrouponeelement,formsNa+,+1charge

Elementsingroup2formmonoatomicionswithchargesequaltotheirgroupnumber

Mgisagrouptwoelement,formsMg2+,+2charge

Elementsingroup17formmonoatomicionswitha-1charge

Example:Cl-,F-,I-

Cations

Monatomiccationsareformedfrommetallicelements

Na+-sodiumion

Zn2+-zincion

Someelementscanformmorethanonecation

ThechargeontheionisindicatedbyaRomannumeralinparenthesesfollowedbythenameofthemetal

Fe2+-iron(II)ion

Fe3+-iron(II)ion

Transitionmetalsoftenformtwoormoredifferentmonoatomiccations

Anions

Monoatomicanionsaretypicallyformedfromnonmetals

Namedbydroppingtheelementnameendingandadding–ide

Cl--chlorideion

F--fluorideion

Commonpolyatomicanions

OH–hydroxideion

CN–cyanideion

Manypolyatomicanionscontainoxygen,theyarecalledoxyanions

Inelementsthatformtwodifferentoxyanions,thenameoftheonethatcontainsmoreoxygenendsin-ate,theonewithlessendsin-ite:

NO2--nitriteion

NO3--nitrateion

Somecompoundshavemultipleoxyanionforms

ClO--hypochloriteion,prefix“hypo”addedtotheoxyanionwiththeleastnumberofoxygen,suffix“-ite”

ClO2--chloriteion

ClO3--chlorateion

ClO4--perchlorateion,prefix“per”addedtothe

oxyanionwiththehighestnumberofoxygen,suffix“-ate”

Manypolyatomicanionswithhigh(negative)chargescan

addoneormorehydrogencations(H+)toformanionswithlowernegativecharge,theirnamingreflectswhethertheH+additioninvolvesoneormorehydrogenions

HSO4--hydrogensulfateion

H2PO4--dihydrogenphosphateion

Acids

AccordingtotheBronsted-Lowerydefinition,anacidisprotondonating(donatesH+).

Anionswithnamesendingin-idehaveassociatedacidsthathavethehydro-prefixandan-icsuffix:

Cl--chlorideion

HCl–hydrochloricacid

Acidsofoxyanions

Iftheoxyanionhasan-ateending,thecorrespondingacidisgivenan-icending

Iftheoxyanionhasan-iteending,thecorrespondingacidhasan-ousending

Prefixesusedinthenamingoftheanionarekeptinthenameoftheacid

ClO--hypochloriteion,HClO-hypochlorousacid

ClO2--chloriteion,HClO2-chlorousacid

ClO3--chlorateion,HClO3chloricacid

ClO4--perchlorateion,HClO4-perchloricacid

MolecularCompounds

Apairofelementscanformseveraldifferentmolecularcompounds

Prefixesareusedtoidentifytherelativenumberofatomsinthesecompounds

COcarbonmonoxide

CO2carbondioxide

Prefixes

Hydrates

Hydratesarecompoundsthatcontainswatermoleculeschemicallyboundtoanothercompoundorelement

Hydratesarefirstnamedfromtheanhydrous(dry)compound

Itisthenfollowedbytheword“hydrate”andaprefixtoindicatethenumberofwatermolecules

CuSO4•5H2O–copper(II)sulfatepentahydrate

MonoatomicCationsandAnions

PolyatomicIons:

MorePolyatomicIons

OxyanionsandtheirAcids

ChemicalEquations

Chemicalreactionsareexpressedthroughchemicalequations

Anarrow(“→”)inachemicalequationmeans“yields”

2H2(g)+O2(g)→2H2O(l)

Hydrogen+oxygenyieldswater

H2andO2arereactants

Substancesthatundergochangeduringareaction

H2Oistheproduct

Substancesformedfromchemicalreactions

Commonphasenotation

g=gas

l=liquid

s=solid

BalancingChemicalEquations

BalancedchemicalequationsadheretotheLawofConservationofMatter

Abalancedequationhastohaveequalnumbersofeachtypeofatomonbothsidesofthearrow

Balancingisdonebychangingthecoefficients

Thecoefficienttimesthesubscriptgivesthetotalnumberofatoms

Iftherearenocoefficientsinfront,coefficientisequaltoone

Ifanatomdoesn’thaveasubscript,subscriptisequaltoone

Subscriptsareneverchanged

CHAPTER3–STOICHIOMETRYOFFORMULASANDEQUATIONS

MassandMoles

Inthemetricsystem,thestandardunitofmassisthegram(orkilogram).

Allelementshaveauniquemass(atomicweight)

Expressedaseitheratomicmassunits(amu)orgrams

Sameweightoftwodifferentelementsrepresentsadifferentnumberofatoms

Considerthereaction:H2+F2→2HF

Doesnotmeanthat1gramofhydrogenwillreactwith1gramoffluorinetoform2gramsofhydrogenfluoride

Inreality2.016gofhydrogenwillreactwith38.000goffluorinetoform40.016ghydrogenfluoride

2.016gofhydrogencontainthesamenumberofH2moleculesas38.000goffluorine(F2)

40.016gramsofHFwillcontaintwiceasmanymolecules

Numberofmolecules,eveninlowmasses,areextremelylargenumbers

Soforconvenience,amountsinchemistryareexpressedinmoles

Mole-quantityofasubstancethatcontainsthesamenumberofatoms,moleculesorformulaunitsasexactly12gofcarbon-12

1mole(mol)=6.0221x1023

Atomicmass–massofonemolecule

Expressedinatomicmassunits(amu)

Molarmass–massofonemoleofentities(atoms,molecules,formulaunits)ofasubstance

Expresseding/mole

Molarmassandatomicmassarenumericallysimilar

Example:onemoleculeofcarbonhasanatomicmassof12.0107amuandamolarmassof12.0107g/mol

In12.0107gofcarbonthereare6.0221x1023molecules

MassPercentage(PercentComposition)

Masspercentageisawayofexpressingtheconcentrationofanelementinacompoundoracompoundofamixture.Stepsforsolvingpercentcomposition(akamasspercentage)questions:

ExampleQuestion:FindthemasspercentagesofC,O,andHinglucose(C6H12O6)

First,lookuptheatomicmassesoftheelementsthatareinthecompoundonaperiodictable

C–12.01g

H–1.01g

O–16.00g

Second,determinehowmanygramsofeachelementareinonemoleofglucose(orwhatevercompoundaquestionmaybeaskingyoufor)

C–(6molesofCx12.01g)=72.06g

H–(12molesofHx1.01g)=12.12g

O–(6molesofOx16.00g)=96.00g

Third,determinethetotalmassinonemoleofthecompoundbyaddingupthemassesoftheelementsfromstep2

Massofonemoleofglucose=180.18g(72.06g+12.12g+96.00g)

Finally,findthemasspercentagesoftheelementsbydividingtheweightofeachelementinonemoleofthecompoundbythemolarmassofthatcompound

C–(72.06g/180.18)x100%=39.99%

H–(12.12g/180.18)x100%=6.73%

O–(96.00g/180.18)x100%=53.28%

Tocheckyourworkyoucanaddupthepercentagestoseeiftheyaddupto100%

39.99%+6.73%+53.28%=100%

Formula

DeterminingEmpiricalFormula

Empiricalformulasarethesmallestwholenumberratioofnumbersoftheatomsinamolecule.Themolecularformulaofacompoundistheformulaofthecompoundasitexists,andmaybeamultipleoftheempiricalformula.

DeterminingEmpiricalFormulafromMasses

ExampleQuestion:Acompoundcontains36.42gofcarbon,6.12gofhydrogen,and47.89gofoxygen,whatisitsempiricalformula?

First,determinethemolesofeachelement

C–(36.42/12.01)=3.03

H–(6.12/1.01)=6.06

O–(47.89/16.00)=2.99

Second,determinethelowestwhole-numberratios;dividethemolesofeachelementbythelowestmoleamount

C–(3.03/2.99)=1.01→1

H–(6.06/2.99)=2.03→2

O–(2.99/2.99)=1.00→1

Thisstepusuallyresultsinratiosthatareveryclosetoawholenumber

However,insomequestionyoumaygetratiosof1.5,or2.5,or3.5,etc.inthiscaseyouwouldmultiplyalltheratiosby2togetwholenumberratios

Insomequestionyoumaygetratiosof1.33,or2.33,or3.33,etc.inthiscaseyouwouldmultiplyalltheratiosby3togetwholenumberratios

Ingeneralterms,iftheratiosarenotveryclosetoawholenumberyouhavetomultiplythembyanumberthatwouldresultinapproximatelywholenumbers

Writetheempiricalformulafromtheresults

CH2O

DeterminingEmpiricalFormulafromElementalAnalysis(%Composition)

ExampleQuestion:Acompoundisfoundtocontain56%carbon,7%hydrogen,and37%oxygen.Whatistheempiricalformulaforthiscompound?Themolecularweightforthiscompoundis86.14g/mol.Whatisthemolecularformula?

First,assumeexactly100gofthecompoundispresent

Thisallowsyoutoexchangepercentageswithgrams

C–56%→56g

H–7%→7g

O–37%→37g

Second,convertmassestomoles

C–(56/12.01)=4.66moles

H–(7/1.01)=6.93moles

O–(37/16.00)=2.31moles

Third,determinethelowestwhole-numberratios;dividethemolesofeachelementbythelowestmoleamount

C–(4.66/2.31)=2.02→2

H–(6.93/2.31)=3.00→3

O–(2.31/2.31)=1.00→1

Writetheempiricalformulafromtheresults

C2H3O

Todeterminethemolecularformulafromtheempiricalformulafollowthesesteps:

Calculatetheweightfromtheempiricalformula(multiplyatomsofeachelementwiththeelementsmolarmassandaddthemup)

2carbonatomsx12.01g=24.02g

3hydrogenatomsx1.01g=3.03g

1oxygenatomx16.00g=16.00g

Total:24.02g+3.03g+16.00g=43.05g

Dividethemolecularweightbytheweightdeterminedfromtheempiricalformulatofindthescalingfactor

86.14/43.05=2.00

Scalingfactoris2

Usingthescalingfactordeterminethemolecularformula

C4H6O2

StoichiometryStoichiometryinvolvesusingrelationshipsbetweenelements,compounds,chemicalformulas,andchemicalreactionstoacquirequantitativedata.Therearefourmajorcategoriesofstoichiometryproblemsthatyouarelikelytoencounter.Theyarelistedbelowwithstrategiesonhowtosolvethem.

ToconvertfromthemassofasubstancetomolesofthatsubstanceyoudividebythemolarmasToconvertfrommolesofasubstancetothemassofasubstanceyoumultiplybythemolarmass

Interconversion:

ThisinterconversionisveryimportantinchemicalcalculationsStoichiometricMole–MoleProblems

ExampleQuestion:HowmanymolesofHClareneededtoreactwith0.82molesofAl?

Writeoutachemicalequationfromtheinformationgiveninthequestion

Al+HCl→AlCl3+H2

Balancethechemicalequation

2Al+6HCl→2AlCl3+3H2

Calculatethemolesofthesubstanceyouaretoldtofindusingmoleratios

StoichiometricMass–MassProblems

ExampleQuestion:HowmanygramsofAlcanbecreatedfromdecomposing12.60gofAl2O3?

Writeoutachemicalequationfromtheinformationgiveninthequestion

Al2O3→Al+O2

Balancethechemicalequation

2Al2O3→4Al+3O2

Convertthemassofthegivensubstanceintomolesofthegiven(mol/g)

Calculatethemolesofthesubstanceyouaretryingtofindthemassforusingmoleratios

Calculatethemassofthesubstanceyouaretoldtofindusingthemolesofthesubstancecalculatedinthepreviousstep

StoichiometricMass-VolumeProblems

ExampleQuestion:HowmanylitersofH2arecreatedfromthereactionof40.00gofKinwater?

Important:1moleofanyidealgaswilloccupy22.41L

Writeoutachemicalequationfromtheinformationgiveninthequestion

K+H2O→KOH+H2

Balancethechemicalequation2K+2H2O→2KOH+H2

Convertthemassofthegivensubstanceintomolesofthegiven(mol/g)

Calculatethemolesofthesubstanceyouaretryingtofindthevolumeforusingmoleratios

Calculatethevolumeofthesubstanceyouaretoldtofindusingthemolesofthesubstancecalculatedinthepreviousstep

StoichiometricVolume-VolumeProblems

ExampleQuestion:HowmanylitersofSO2willbeproducedfrom28.3LO2?

Important:1moleofanyidealgaswilloccupy22.41L

Writeoutachemicalequationfromtheinformationgiveninthequestion

S2+O2→SO2

Balancethechemicalequation

S2+2O2→2SO2

Convertthevolumeofthegivensubstanceintomolesofthegiven(mol/g)

Calculatethemolesofthesubstanceyouaretryingtofindthevolumeforusingmoleratios

Calculatethevolumeofthesubstanceyouaretoldtofindusingthemolesofthesubstancecalculatedinthepreviousstep

LimitingReagent

Typicallyoneofthereactantsinachemicalreactionispresentinsmallerstoichiometricamountsthantheotherreactant(s)

Thislimitstheamountofproduct(s)thatcanform

Limitingreagentproblemsareeasytoidentify

Theproblemwillgivetheamountsofmorethanoneofthestartingmaterials

Youwillhavetodeterminethelimitingreagentfromcalculationsinordertosolvetheproblem

Therearetwotypicalmethodsofdeterminingthelimitingreagent

Needvs.HaveMethod

ProductMethod

Needvs.HaveMethod

Pickoneofthereactants(Reac1),calculatehowmuchoftheotherreactant(Reac2)youwillneedtocompletelyreactwithReac1

Utilizestoichiometricratios

Thisrequiresabalancedequation!

Makesuretheequationisbalancedbeforeyoubeginworkingontheproblem

ComparetheamountneededfortheReac2withtheactualamountlistedinthequestion

IftheamountyouneedisMOREthanwhatyouactuallyhaveavailableaccordingtotheproblemthenReac2isthelimitingreagent

IftheamountyouneedisLESSthanwhatyouactuallyhaveavailableaccordingtotheproblemthenReac1isthelimitingreagent

Youfinishtherestoftheproblembasedonthereactantyoufoundtobelimiting

“Product”Method

Pickoneoftheproductsofthereaction

Chooseoneofthereactants(Reac1)andcalculatehowmuchoftheproductyoucanmakeusingtheamountyouhaveavailableaccordingtothequestion

Makethesamecalculationusingtheotherreactant(Reac2)

Thereactantthatresultsinthesmallestamountofproductisthelimitingreagent

Theamountisalsothemaximumamountofproductthatcanbemade

Thisamountiscalledthe“theoreticalyield”

ReagentinExcess

Somequestionsmayaskyoutodeterminehowmuchoftheexcessreagentwillbeleftoveroncethereactionends

Tocalculatethisvalue

Calculatehowmuchoftheexcessreagentisneededtocompletelyreactwiththelimitingreagent

Takethedifference(subtract)offtheamountofexcessreagentyouhadatthebeginningandtheamountneededtocompletelyreactwiththelimitingreagent

PercentYield

Itisverycommonthattheamountofproductmadeexperimentallyislowerthantheamountexpectedbythetheoreticalyield

Thisoccursbecauseofmechanicalerrors,incompletereactions,“side”reactions,etc.

Todeterminethepercentyield(sometimesalsocalledtheefficiencyofareaction)usethefollowingformula:

CHAPTER4–CHEMICALREACTIONS

WaterasaSolvent

Mostreactionsthatoccurinorganismsandtheenvironmenttakeplaceinwater

Waterhas2hydrogenatomscovalentlybondedto1oxygenatom

Theelectronicstructureofwateristetrahedral

2covalentbondswithHatomsand2setsofunpairedelectrons

104.5˚bondangle–becausethetwolonepairstrytoseparateasfaraspossible

Waterisapolarmolecule

Polaratomshavedipolesbecauseofunequalsharingofelectrons

Thesharedpairofelectronsareattractedmorestronglytotheoxygenformingapartiallynegativecharged“pole”neartheoxygenandpartiallypositivelychargedpolesneartheHydrogens

StructureofWaterwithDipoles:

Solubility

Solublesubstances(solutes)inwater

Interactionbetweenanionandwaterisstrong

Polarcompoundsarewatersoluble

Polarwatermoleculeshaveanaffinityforoppositelychargedregionsofotherpolarmolecules

Insolublesubstances(solutes)inwater

Non-polarcompoundsarenotwater-soluble

Iftheinteractionbetweenionandwaterisweak

Insolublesubstanceshaveaforceofattractionsostrongintheirsolidsubstanceform,thatitcannotbeovercomebytheinteractionoftheionswiththepolarizedwatermolecules

IonsinAqueousSolution

Inionicsolids,cations&anionsareheldtogetherbyelectrostaticattraction

Theelectrostaticattractionisreplacedbywatermoleculesinanaqueoussolution

Manyioniccompoundsdissociateintoindependentionswhendissolvedinwater

Compoundsthatfreelydissociateintoindependentionsinaqueoussolutionarecalledelectrolytes

Solutionswithelectrolytesaregoodconductorsofelectricity

Notallelectrolytesareioniccompounds

Somemolecularcompoundsdissolvebutdonotdissociateintoions

Containpolarbondswhichinteractwiththepolarbondsinwater

Donotconductanelectriccurrent

Produceanonconductingsolution

Referredtoasnonelectrolytes

StrongandWeakElectrolytes

Strongelectrolyte-anelectrolytethatcompletelydisassociatesinsolution

Existinsolutionalmostentirelyasions

Weakelectrolyte-anelectrolytethatdoesnotcompletelydisassociateinsolution

Existsinsolutionasbothionsandmoleculesoftheelectrolyte

MolecularandIonicEquations

Molecularequationexpressreactantsandproductsasiftheyweremolecules,despiteactuallyexistinginsolutionasions

Exampleofamolecularequation

CaCl2(aq)+2AgNO3(aq)⇌ Ca(NO3)2(aq)+2AgCl(s)

(aq)isusedtoindicatethatthesubstanceisactuallydisassociatedinsolution

(s)isusedtoindicatethatthesubstanceisaprecipitate

Ionicequationexpressstrongelectrolytesasseparateindependentions

Exampleofanionicequation

Ca2+(aq)+2Cl-(aq)+2Ag+(aq)+2NO3-(aq)⇌ Ca2+

(aq)+2(NO3)-(aq)+2AgCl(s)

Notethatthesolidiswritteninitsfullformula

Netionicequationareequationswithoutanyspectatorions

Spectatorion-anioninanionicequationthatdoesnottakepartinthereaction

Easywayofidentifyingspectatorionsisbywritingtheionicequationandthencrossingoffanyionsthatappearonbothsidesoftheequation(thosearethespectatorions)

Example:

Ca2+(aq)+2Cl-(aq)+2Ag+(aq)+2NO3-(aq)⇌

Ca2+(aq)+2(NO3)-(aq)+2AgCl(s)

Resultingnetequation:2Cl-(aq)+2Ag+(aq)⇌ 2AgCl(s)

ThreeMajorClassesofChemicalReactions

Thethreemajorclassesofchemicalreactionsare:precipitationreactions,acid-basereactions,andoxidation-reductionreactions.

PrecipitationReactions

Precipitationreactionoccursinaqueoussolutionbecauseoneoftheproductinaprecipitationreactionisinsoluble

Precipitate-aninsolublesolidcompoundformedduringachemicalreactioninsolution

Therearegeneralizedsolubilityrulesthatareusedtopredictwhetheraprecipitatewillform

Soluble-allcompoundscontainingtheammoniumion(NH4

+)oralkalimetal(GroupIAontheperiodictable)cations

Soluble-allnitratesandacetates(ethanoates)

Soluble-allchlorides,bromidesandiodides

ExceptthosewithAg,Pb,Hg

Soluble-allsulfates

ExceptthosewithAg,Pb,Hg(I),Ba,Sr,Ca

Insoluble-allcarbonates,sulfites,andphosphates

Exceptthosewithammonium(NH4+),andalkali

metal(GroupIA)cations

Insoluble-allHydroxides

ExceptthosewithNH4+,alkalimetal(GroupIA)

cations

Insoluble-allsulfides

ExceptthosewithNH4+,alkalimetal(GroupIa)

cations,andalkaliearthmetal(GroupII)cations

Insoluble-alloxides

ExceptthosewithCalcium,Barium,andalkalimetal(groupIA)cations

SolubilityRulesTables:

Precipitationreactionstaketheformofan“exchangereaction”

Exchangereactionsarereactionbetweencompoundsthatappeartoinvolveanexchangeofcationsandanions

Acid-BaseReactions

TheArrheniusdefinitionofacidsandbases

Acidsproducehydrogenions(H+)whendissolvedinwater

Basesproducehydroxideions(OH-)whendissolvedinwater

Bronsted-Lowerydefinitionofacidsandbases

Acidsareprotondonating

Basesareprotonaccepting

Strongacid–anacidthationizescompletelyinwater

StrongacidsareHI,HBr,HClO4,HCl,HClO3,H2SO4,andHNO3

Weakacid–anacidthatonlypartiallyionizesinwater

Strongbase–abasethatispresentalmostentirelyasions(oneoftheionsisOH-)

StrongbasesareNaOH,KOH,LiOH,RbOH,CsOH,Ca(OH)2,Ba(OH)2,andSr(OH)2

Weakbase–abasethatonlypartiallyionizesinwater

Strongacidsandbasesarerepresentedasseparateionsinanionicequation

Weakacidsandbasesarerepresentedasundissociated“molecules”inionicequations

ExampleofAceticAcid(aweakacid)

MolecularEquation:CH3COOH(aq)+NaOH(aq)→

CH3COONa(aq)+H2O(l)

Ionic:CH3COOH(aq)+Na+(aq)+OH-(aq)→CH3COO-(aq)+

Na+(aq)+H2O(l)

Net:CH3COOH(aq)+OH-(aq)→CH3COO-(aq)+H2O(l)

Neutralization(Acid-Base)Reactions

Acidsandbasesneutralizeoneanother

Neutralizationreaction-reactionbetweenanacidandabasethatresultsinanioniccompoundandwater

Salt-ioniccompoundthatistheproductofaneutralizationreaction

Netionicequationforeachneutralizationreactioninvolvesatransferofaproton

ConsidertheexampleofHCl(astrongacid)reactingwithLiOH(astrongbase)

Netequationforthereactionis:H+(aq)+OH-(aq)→

H2O(l)

ConsidertheexampleofHCN(aweakacid)reactingwithKOH(aweakbase)

HCN(aq)+OH-(aq)→CN-(aq)+H2O(l)

TheprotonistransferredfromHCNtoOH-

Acid-BaseReactionswithGasFormation(akaDisplacementReactions)

Acid-basereactionswithgasformationsometimesinvolveunstablechemicalspecies(e.g.,H2CO3andH2SO3

Unstablespeciesareenclosedinparentheses

Example:[H2CO3(aq)]→H2O(l)+CO2(g)

Oxidation-ReductionReactions(akaRedoxReactions)

Oxidation-reductionreactions(akaredoxreactions)–reactionsthatinvolveapartialorcompletetransferofelectronsfromonereactanttoanother

Oxidation=lossofelectrons

Reduction=gainofelectrons

Trickforrememberingwhichiswhich-OILRIG

OIL-OxidationIsLosingelectrons

RIG-ReductionIsGainingelectrons

Oxidationandreductionalwaysoccursimultaneously

Oxidationnumber(akaoxidationstate)–actualchargeanatominamoleculewouldhaveifalltheelectronsitwassharingweretransferredcompletely,notshared

Oxidizingagent–speciesthatoxidizesanotherspecies

Itisitselfreduced

Reducingagent–speciesthatreducesanotherspecies

Itisitselfoxidized

ReducingandOxidizingAgents:

OxidationNumberRules

CommonRedoxReactions

Combination-reactioninwhichtwosubstancecombinetoformathirdsubstance

Decomposition–reactioninwhichasinglecompoundproducestwoormoresubstances

Displacement(akasingle-replacementreaction)–reactioninwhichanelementreactswithacompoundanddisplacesanelementfromit

Combustion–reactioninwhichoneofthereactantsisoxygen

Usuallyresultsintherapidreleaseofheat

Redoxreactionscanbewrittenintermsoftwohalf-reactions

Oneinvolvesthelossofelectrons(oxidation)

Theotherinvolvesthegainofelectrons(reduction)

Example:Fe2++Ce4+→Fe3++Ce3+

Abalancedredoxequationhastohavechargebalance

Numberofelectronslostintheoxidationhalf-reactionmustbeequaltothenumberofelectronsgainedinthereductionhalf-reaction

CHAPTER5–QUANTUMTHEORYANDATOMICSTRUCTURE

EmissionSpectrum

Whenelementsareburnedinaflameandtheiremissionsarepassedthroughaprismonlyafewcolorlinesareseen

Theselinesareadistinctcharacteristicofeachelement

Atomsemitlightofacharacteristicwavelengthswhentheyreturnfromanexcitedstatetotheirgroundstate

EmissionSpectrumofHydrogen:

LightLightisaformofelectromagneticenergythatbehavesasbothawaveandaparticle.

LightasaWave

ElectromagneticenergytravelsinrhythmicwaveswhicharedisturbancesofelectricandmagneticfieldsWavelength(λ)-distancebetweenconsecutivecrestsofelectromagneticwaves

Wave:

Frequency(f)–numberofcrestsofawavethatmovepastagivenpointinagivenunitoftime

f=λ/vv=speed

Speedoflightinavacuum=2.998x108m/secTheelectromagneticspectrumencompassesaverywiderangeofwavelengthsfromassmallasananometertothosethataremorethanakilometer

LightasaParticle

LightalsobehavesasifitconsistsofdiscreteparticlesorquantacalledphotonsEachphotonhasafixedquantityofenergy

E=hc/λhisthePlanck’sconstant=6.626X10-34joules•seccisthespeedoflightinavacuum=2.998X108m/sec

Shorterλ=higherenergy

Wave-ParticleDualityAllmatterandenergyexhibitbothwaveandparticle-likepropertiesThisdualityisseenin:

MacroscopicobjectsMicroscopicobjects(e.g.atomsandmolecules)Quantumobjects(e.g.,protons,neutrons,quarks,mesons)

ToexplainWave-ParticlesDuality,physicistsfocusedon3phenomena

BlackBodyRadiationPhotoelectricEffectAtomicLineSpectra

BlackBodyRadiation

Asthetemperatureofanobjectchanges,itstemperatureisdirectlyrelatedtothewavelengthsoflightthatitemits.Thisisacharacteristicoftheidealized“blackbody.”

MaxPlanckdevelopedamathematicalmodeltoreproducethespectrumoflightemittedbyglowingobjects

Themodelwasdevelopedundertheassumptionthatavibrating(oscillating)atomcanonlyemitorabsorbcertainquantitiesofenergy

Planck’sModel

E=nhv

E-energyofradiation

v–frequency

n–quantumnumber(1,2,3…)

h–Planck’sConstant=6.626x10-34J•s

Quanta–packetsofenergythatcanbeemittedorabsorbed

Atomschangeenergystateswhentheyemitorabsorboneormorequanta

Themodelviewsemittedenergyaswaves

PhotoelectricEffect

Thephotoelectriceffectistheobservationthatmanymetalsemitelectronswhenlightshinesuponthem.Electronsemittedinthismannerarecalledphotoelectrons.

Electronsareejectedfromthesurfaceofthemetalonlywhenthefrequencyexceedsacertainthreshold

Thethresholdisdependentonthecharacteristicofthemetal

Einsteinreasonedthatatomschangeenergystateswhentheyemitorabsorbaquantumoflightenergy,whichhecalledaphoton

Hedefinedaphotonasaparticleofelectromagneticenergy

Accordingtothephotoelectriceffect

Electronsexistindifferentenergystates

Aphotonwhosefrequencyisgreaterthanorequaltotheenergystateoftheelectronwillbeabsorbed

Ifthefrequencyislessthantheelectronenergylevel,thephotonisnotabsorbed

Theelectronmovestoahigherenergystateandisejectedfromthesurfaceofthemetalwhenitabsorbsaphoton

Electronsareattractedtothepositiveanodeofabatterywhichcausesaflowofcurrent

AtomicLineSpectra

Whenlightfroman“excited”atompassesthroughaprism,itdoesnotformacontinuousspectrum

Instead,itproducesaseriesofcoloredlinescalled“linespectra”thatareseparatedbyblackspaces

Wavelengthsofthelinesareacharacteristicoftheelementsproducingthem

Differentelementshavedifferentlinespectra

ExampleofHydrogen

ThespectralinesofHydrogenoccurinseveralseries

Eachseriesisrepresentedbyapositiveinteger,n

LineSpectraofHydrogen:

Ultravioletseries,n=1

Visibleseries,n=2

Infraredseries,n=3

ThevisiblespectrumofHydrogencanbereproducedbyaRydbergEquation

R–RydbergConstant=1.096776x107

m-1

Λ–wavelengthofthespectraline

n1andn2arepositiveintegerswheren2>n1

BohrTheory

Bohr’stheoryofanatomwasanearlymodelofatomicstructureinwhichelectronstravelaroundthenucleusinanumberofdiscretestableorbitsdeterminedbyquantumconditions.

Bohrcameupwith2postulatestoaccountforhowelectronsloseenergyyetremaininorbit

Aelectronhasspecificenergylevelsinanatom

Aelectroninanatomchangesenergylevelsbyundergoingatransitionfromoneenergyleveltoanother

Bohrcameupwithaformulafortheenergylevelsoftheelectroninthehydrogenatom

E=-2.18x10-18J

n–principalquantumnumbers=1,2,3…

Z–nuclearcharge

Z=1forHydrogen

Whenanelectronundergoesatransitionfromahigherenergylevel(ni)toalowerone(nf)theenergyisemittedasaphoton

E=hv=Ef–Ei=∆E

E–energyofemittedphoton

Ei=

Ef=

∆E=hv=-2.18x10-18J

QuantumMechanics

Quantummechanicsisthebranchofphysicsthatattemptstomathematicallydescribethewavepropertiesofsubmicroscopicparticles.

deBroglierelation

λ=h/mv

Matterhaswave-likepropertiesbutthesepropertiesarenotcommonlyobserved

deBroglierelationshowsthatthewavelengthofobjectsissoincrediblysmallthatthesewavescannotbedetected

Heisenberg’sUncertaintyPrinciple

Statesthatyoucanneverknowtheexactpositionandtheexactspeedofanobjectwithhighprecision

Essentially,thereisanuncertainty

Theprincipleisalsoarelationshipthatstatesthattheproductoftheuncertaintyinposition(∆x)andtheuncertaintyinmomentum(m∆vx)ofaparticlecanbenosmallerthanwhatispredictedbytheequation:

(∆x)(m∆vx)>

=5.28x10-35J•s

Whenmislarge(representsalargeobject)theuncertaintyisverysmallbutforsubatomicparticleslikeelectronthereisahighlevelofuncertainty

Thisuncertaintyiswhywecan’tdefinetheexactorbitofanelectron

Schrodingerdevelopedaquantummechanicalmodelofthehydrogenatom.Accordingtothemodel:

Anatomhasspecificallowedquantitiesofenergy

Anelectron’sbehavioriswave-like

However,itsexactlocationisimpossibletoknow

Theelectron’sMatter-Waveoccupiesa3-Dspacenearthenucleus

TheMatter-Waveexperiencescontinuousandvaryinginfluencefromthenuclearcharge

SchrodingerEquation

H(op)Ψ=EΨ

E–energyoftheatom

Ψ–wavefunction

H(op)–HamiltonianOperator

QuantumNumbersandAtomicOrbitals

Quantummechanicsdescribeseachelectronby4quantumnumbers

PrincipalQuantumNumber(n)

AngularMomentumQuantumNumber(l)

MagneticQuantumNumber(m l )

SpinQuantumNumber(ms)

n, l ,m l definethewavefunctionoftheelectron’s

atomicorbital

msreferstothespinorientationofthe2electronsthatoccupyanatomicorbital

PrincipalQuantumNumber(n)representsthe“shellnumber”inwhichanelectronislocated

Representstherelativesizeoftheorbital

Definestheprincipalenergyoftheelectron

Smaller“n”representsasmallerorbitalandalowerenergyoftheelectron

ncantakeanypositivevalue

AngularMomentumQuantumNumber( l )representsthe“subshells”withinagivenshell

Eachmain“shell”isdesignatedbyaquantumnumber“n”

Itisfurthersubdividedinto:l =n-1“subshells”

“ l ”canhaveanyintegervaluefrom0ton-1

“ l ”valuescorrespondtothes,p,d,fdesignationsusedintheelectronicconfigurationoftheelements

shasan l valueof0

phasan l valueof1

dhasan l valueof2

fhasan l valueof3

MagneticQuantumNumber(m l )definesatomicorbitalswithinagivensub-shell

Eachvalueoftheangularmomentumnumber( l )determinesthenumberofatomicorbitals

Foranygivenvalueof“ l ,”mlcantakeanyintegervaluefrom- l to+ l

m l =- l to+ l

Eachorbitalhasadifferentshapeandorientation(x,y,z)inspace

Eachorbitalwithinagivenangularmomentumnumbersubshell( l )hasthesameenergy

SpinQuantumNumber(ms)representsthetwopossiblespinorientationsofanelectronresidingwithinagivenatomicorbital

Eachatomicorbitalholdsonlytwoelectrons

Eachelectronhasa“spin”orientationvalue

Thesevaluesmustbeoppositeofoneanother

Possiblevaluesofmsare:+½and-½

SummaryofQuantumNumbers

Shapesoforbitals

s(n=1)subshellorbital

Onlyoneorbital,holds2electrons,sphericalshape

p(n=2)subshellorbitals

Threeorbitals,holds6electrons,dumbbellshape

d(n=3)subshellorbital

Fiveorbitals,holds10electrons,pear-shapedlobesanddumbbellshapes

f(n=4)subshellorbitals

Sevenorbitals,holds14electrons

CHAPTER6–ELECTRONCONFIGURATION

ANDPERIODICPROPERTIES

BriefReviewtoUnderstandElectronConfiguration

Thequantumnumbersn, l ,m l defineanorbital

Aorbitalcontainsamaximumof2electrons

Eachelectronhasadifferentspin(+½or-½)

Orbitaldiagramsarenotationsusedtoshowhowtheorbitalsofasubshellareoccupiedbyelectrons

Eachgroupoforbitalsislabeledbyitssubshellnotation(s,p,d,f)

Electronsarerepresentedbyarrows

Up↑forms=+½

Down↓forms=-1/2

ExampleofanOrbitalDiagram:

PauliExclusionPrinciple

Notwoelectronsinanatomcanhavethesamefourquantumnumbers

Summarytableforthemaximumnumberofelectronsineachsubshell:

ElectronConfigurationTheelectronconfigurationofanatomreferstotheparticulardistributionofelectronsamongtheavailablesubshellinthatatom.

Electronicconfigurationnotationlistssubshellsymbols(s,p,d,f)sequentiallywithasuperscripttoindicatethenumberofelectronsinthatsubshell

Ex.Fluorine

AtomicNumber:9

NumberofelectronsinaneutralFluorineatom:9

Numberofelectronsforaneutralatomisthesameastheatomicnumber

2electronsinthe“1s”subshell

2electronsinthe“2s”subshell

5electronsinthe“2p”subshell

ElectronConfiguration:1s22s22p5

Configurationscanbecomequitecomplexasatomicnumberincreases

Toremedythis,acondensedformoftheconfigurationisoftenusedwhichutilizeselectronconfigurationsofnoblegases

Noblegaseshavethemaximumnumberofelectronspossibleintheiroutershell

Makesthemveryunreactive

Thenoblegasesare:helium,neon,argon,krypton,xenon,andradon

TableofCondensedElectronicConfigurationExamples:

[X]representstheelectronconfigurationofthenearestnoblegasthatappearsbeforetheelementofinterestontheperiodictable

Keepinmindthatyouhavetoadjustthenumberofelectronsandthustheelectronconfigurationforcationsandanionsofanelement

NuclearCharge,ShieldingEffect,andOrbitalShapeNuclearCharge

Inanatomthereare2counteractingforces:

Inthenucleus

Positiveprotonspull(attract)thenegativelychargedelectrons

Outsidethenucleus

Negativelychargedelectronsarerepellingeachother

Highernuclearcharge(Z)lowersorbitalenergybyincreasingtheamountofproton-electronattractions

Loweringorbitalenergymakesitmoredifficulttoremovetheelectronfromorbit

ShieldingEffect

Therepulsionelectronsexperiencefromotherelectronsshields(counteracts)theattractiveforceoftheprotonsinthenucleus

Shieldinglowersthefullnuclearchargetoan“effectivenuclearcharge”(Zeff)

Loweringtheeffectivenuclearchargemakesiteasiertoremoveanelectron

IttakeslessenergytoremoveanelectronfromHelium(He)thanfromHe+

SincethesecondelectroninHerepelsthefirstelectronandeffectivelyshieldsthefirstelectronfromthefullnuclearcharge

EffectsofOrbitalShape

Shapeofanatomicorbitalaffectshowcloseanelectroncomestothenucleus(i.e.thelevelofpenetration)

Penetrationandshieldingcausetheenergylevel(n)tobesplitintosublevelsofdifferingenergy

Thisisrepresentedbythevariousvaluesofthemagneticquantumnumber( l )

Thelowerthevalueofthemagneticquantumnumber,thegreatertheelectronpenetration

OrderofSublevelEnergies

s( l=0)<p( l=1)<d( l=2)<f( l=3)

AufbauPrinciple

TheAufbauprinciplestatesthatelectronsorbitingoneormoreatomsfillthelowestavailableenergylevelsbeforefillinghigherlevels.Forexample,anelectronhastofillthe“1s”before“2s.”

Fillingorbitalsofthelowestenergyfirstgivesthelowesttotalenergyoftheatom

Thegroundstateoftheatom

Orderinwhichthepossiblesubshellsfill

1s,2s,2p,3s,3p,4s,3d,4p,5s,4d,5p,6s,4f,5d,6p,7s,5f

OrderofFillingSubshells:

Orderinwhichsubshellsarefilledisintheorderinwhichthediagonallinesgothroughthesubshells

Note:4ssubshellisfilledbeforethe3dsubshellbecause4selectronsareatalowerenergylevelthanthe3delectrons

Lowerenergylevelsarealwaysfilledfirst

Configurationassociatedwiththelowestenergylevelofanatomisthegroundstate

Anyotherconfigurationscorrespondtotheexcitedstates

Hund’sRuleHund’srulestatesthatthe“groundstate”(i.e.thelowestenergyconfiguration)ofelectronsinasub-shellisattainedfromputtingelectronsintoseparateorbitalsofasubshellbeforepairingtheelectrons.

Example:OxygenOxygenOrbitals:

Note:Twooftheelectronsinthe2porbitalsappearsinglyinsteadofbeingpairedtogether

AccordingtoHund’sRule,electronsoccupyseparateorbitalsratherthanpairingwhenpossible

ConfigurationsandthePeriodicTable

Electronsinanatom’soutermostshellarecalledvalenceelectrons

Valenceelectronsaretheelectronsprimarilyinvolvedinchemicalreactions

Elementswithinagrouphavethesamevalenceshellconfiguration

Thisiswhygroupsofelementssharechemicalproperties

Noblegaseshavefilledoutershells

Veryhighionizationenergies

Positive(endothermic)electronaffinities

Donotreadilyformionsorreact

Inertforthemostpart

Verystable

Otherelementstrytoattainnoblegasconfiguration(filledoutershells)forstability

ElementsinGroups1Aand2Areadilyformcationsbylosingelectrons

Theyonlyhave1or2electronsintheiroutershellsrespectively,losingtheirvalenceelectronsallowstheseelementstoconformtonoblegasconfiguration

ElementsinGroups6Aand7Areadilyformanionsbygainingelectrons

Theyfilltheiroutershellsandconformtoanoblegas

configuration

Theyareisoelectronicwiththenearestnoblegasconfiguration

Isoelectronic–havethesamenumberofelectronsorthesameelectronicstructure

LargemetalsfromGroups3A,4A,and5Aformcationsthroughadifferentprocessthanthesmaller1Aand2Aelements

Theyhavetoloselargeamountsofelectronsinordertoattainnoblegasconfiguration

Example:Tin(Sn),wouldhavetolosetwoelectronsfrom5p,tenfrom4d,twofrom5sinordertobeisoelectronicwithKrypton

ForTinitiseasiertogainstabilitybyreachinganoblegas-likeconfigurationbyhavingempty5s&5psublevelsandafilledinner4dsubshellconfiguration

Manytimesitisonlyimportanttoknowthevalenceelectronnumberforanatom

Ontheperiodictableitiseasytodeterminethis:thenumberofvalenceelectronsforanatommatchesitsgroupnumber

Example:Group7Aelementshave7valenceelectrons

PeriodicProperties

PeriodicLawstatesthatwhenelementsarearrangedbyatomicnumber,theirphysicalandchemicalpropertiesvaryacrosstheperiodictablerow.

AtomicSize

Twofactorsthataffectsizeofanatom

Largertheprincipalquantumnumber(n),thelargerthesizeoftheorbit

Effectivenuclearcharge

Positivechargeanelectronexperiencesfromthenucleusminusanyshieldingeffects

Atomicradiustendstodecreasewithincreasingatomicnumberacrossaperiod

Thereisahighereffectivenuclearcharge

Greaterattractiveforceinthenucleusfromthehighernumberofprotons

Atomicradiustendstoincreasewithincreasingatomicnumberwithinagroup

Moreenergylevels

Eachsubsequentenergylevelisfurtherfromthenucleusthanthelast

IonicSize

Cationsaresmallerthantheirneutralatomcounterparts

Electronsareremoved

Resultsinadecreaseinelectronrepulsion

Allowsnuclearchargetopullelectronscloser

Anionsarebiggerthantheirneutralatomcounterparts

Electronsareadded

Resultsinanincreaseinelectronrepulsion

Occupymorespace

Ionicsizeincreasesdownagroup

Moreenergylevels

Ionicsizeisslightlycomplicatedacrossaperiod

Decreasesamongcations

Increasesdramaticallywiththefirstanion

Decreaseswithinanions

IonizationEnergy(IE)

Firstionizationenergy-theminimalenergyneededtoremoveoneoftheoutermostelectronsfromaneutralatom

Successiveelectronremovaliscalledsecondionizationenergy,thirdionizationenergy,etc.

Successiveionizationenergiesincreasebecauseeachelectronthatispulledawaycreatesalargerpositivecharge(i.e.ahighereffectivenuclearcharge)

Ionizationenergiestendincreasewithatomicnumberwithinaperiod

Moredifficulttoremoveanelectronthatisclosertothenucleus

Remember:Thereisahighereffectivenuclearchargeacrossaperiod

Ionizationenergiestendtodecreasedownagroup

ElectronAffinity

Thisisnotthesameaselectronegativity!

Morenegativeelectronaffinityvalueexpressthatamorestablenegativeionisformed

Negativevaluesindicatethatenergyisreleasedwhentheanionforthatelementforms

Generaltrendisthatvaluesbecomemorenegativefromlowerlefttoupperright

HighestelectronaffinitiesoccurforFandCl

Electronegativity

Electronegativityisthemeasureofanatom’sabilityoftodrawbondingelectronstoitselfinamolecule

Electronegativitytendstoincreasefromthelower-leftcornertothe

upper-rightcorneroftheperiodictable

Metals,NonMetals,andMetalloidsMetals

TypicalProperties

Shinysolids

Highmeltingpoints

Goodthermal&electricalconductors

Malleable

Losetheirelectronstononmetals

NonMetals

TypicalProperties

Notshiny

Lowmeltingpoints

Poorthermal&electricalconductors

Crumblysolidsorgases

Gainelectronsfrommetals

Metalloids(Semi-metals)

Elementsthatexhibitsexternalcharacteristicsofametal,butbehaveschemicallyasanonmetal

TypicalProperties

Makegoodsemiconductors

Haveintermediateconductivity

Intermediateelectronegativityvaluesandionizationenergies

Reactivitydependsontheelementwithwhichtheyarereacting

Donotformmultiplebonds

Compoundswithmetalloidsoftenhaveincompleteoctetaroundthecentralatom

Boilingpoints,meltingpoints,anddensitiesvarywidely

MetallicBehaviorTrends

Metallicbehaviordecreasesacross(lefttoright)aperiodandincreasesdownagroup

CHAPTER7–CHEMICALBONDING

IonicBonds

Ionicbondsarechemicalbondsformedbytheelectrostaticattractionbetweenpositiveandnegativeions.

Ionicbondsinvolvethetransferofelectronsfromoneatomtoanother

UsuallythetransferisfromametalfromGroupIAorIIAtoanonmetalfromGroup7AorthetopofGroup6A

Numberofelectronslostorgainedbyanatomisdeterminedbyitsneedtobeisoelectronicwithitsnearestnoblegas

Noblegasconfigurationsareextremelystable

Ionicbondsresultintheformationofionsthatareelectrostaticallyattractedtooneanother

Anion–negativelychargedion

Sizeofananionislargerthantheoriginalsizeoftheneutralatom

Cation–positivelychargedion

Sizeofacationissmallerthantheoriginalsizeoftheneutralatom

PropertiesofIonicCompounds

Hard:don’tdent

Rigid:don’tbend

Brittle:crackbutdon’tdeform

Theabovepropertiesarearesultofthepowerfulattractiveforcesholdingionstogether

Movingionsoutofpositionrequireslargeamountsofenergytoovercometheattractiveforces

CovalentBonds

Twononmetalsoftenformcovalentbonds

Shareelectronssincetheyhavesimilarattractionsforthem

Eachnonmetalholdstightlytoitsownelectrons

Sharedelectronpairspendmostoftheirtimebetweenthetwoatoms

Electronpairsbeingsharedaresaidtobelocalized

Howcovalentbondsform

Distancebetweentwonucleidecreases

Eachstartstoattracttheother’selectron(s)

Causesadecreaseinpotentialenergy

Atomsdrawcloserandclosertogether

Energybecomesprogressivelylower

Attractionsincreasebutsodoesrepulsionsbetweenelectrons

Ataparticularinternucleardistance,maximumattractionisachieved

Balancebetweennucleus-electronattractions

Balancebetweenelectron-electronandnucleus-nucleusrepulsions

Twosetsofforcesareinvolvedwithincovalentcompounds

Strongcovalentbondingforcesholdatomstogetherwithinthemolecule

Weakintermolecularforcesholdseparatemoleculesneareachother

Weakintermolecularforcesbetweenmoleculesareresponsiblefortheobservedphysicalpropertiesofthesemolecules

TypesofCovalentBonds

Coordinatecovalentbond–covalentbondinwhichbothofthesharedelectronsaredonatedbyasingleatom

Doublebond–sharingoftwopairsofelectronsbetweenatoms

Triplebonds–sharingofthreepairsofelectronsbetweenatoms

Polarcovalentbond–covalentbondwherethebondingelectronspendmoretimeclosertooneoftheatomsinvolvedinthebonding

Nonpolarcovalentbond–covalentbondwherethebondingelectronsaresharedequally

BondingPairsandLonePairs

Sharedelectronsareconsideredasbelongingentirelytoeachatominacovalentbond

Sharedelectronpairsimultaneouslyfillstheouterlevelofbothatoms

Anouter-levelelectronpairthatisnotinvolvedinbondingisa“lonepair”

Metal-MetalBondingMetalshavelowionizationenergies

LoseelectronseasilyDonotgainthemreadily

Valenceelectronsareevenlydistributedaroundmetal-ioncoresMetal-ioncoresconsistofthenucleusplustheinnerelectrons

ValenceelectronsaredelocalizedMovefreelythroughoutthemetal

PredictingIonicandCovalentBonding

Non-polarcovalentbond

Typicallyelectronegativitydifferencebetweenthetwoatomshastobelessthan0.5fornon-polarbonds

Polarcovalentbonds

Electronegativitybetweenthetwoatomsisdifferentbyagreaterdegreethan0.5butlessthan2.0

Ionicbonds

Typically,differenceinelectronegativityismorethan2.0

BondLength,BondOrder,andBondEnergy

Bondorder-measureofthenumberofbondingelectronpairsbetweenatoms

Singlebondshaveabondorderof1

Doublebondshaveabondorderof2

Triplebondshaveabondorderof3

Fractionalbondordersarepossibleinmoleculesandionsthathaveresonancestructures

Bondlength(akabonddistance)–distancebetweenthenucleiinabond

Bondlengthdependsonbondsorder

Increaseinbondordermeansashorterandstrongerbond

BondEnergy(BE)–measureoftheamountofenergyrequiredtobreakapartonemoleofcovalentlybondedgases

Quantityofheatabsorbedtobreakreactantbondsisdenoted∆H˚reactants

Quantityofheatreleasedtoformproductbondsisdenoted∆H˚products

Exothermicreactions

∆H˚rxnisnegative

Endothermicreactions

∆H˚rxnispositive

CHAPTER8–GEOMETRYOFMOLECULES

LewisDotStructures

LewisStructureofCarbon:

Lewisdotstructuresrepresentelectronsinthevalenceshellofanatomorionasdotsplacedaroundthelettersymboloftheelement

Bondingelectronpairsarerepresentedbyeithertwodotsoradash

LewisElectron-dotFormulaExample:

RulesforFormingLewisStructures

Calculatethenumberofvalenceelectronsforthemolecule

Group#foreachatom(1-8)

Givesvalenceelectronnumberforeachatom

Addallnumbersup

Addthechargeofanyanions

Example:ananionwitha-2chargehas2extraelectrons,youwouldadd2tothetotalcount

Subtractthechargeofanycations

Example:acationwitha+3chargelacks3electrons,youwouldsubtract3fromthetotalcount

Placetheatomwiththelowestgroupnumberandlowestelectronegativityasthecentralatom

Arrangetheotherelementsaroundthecentralatom

Distributeelectronstoatomssurroundingthecentralatomtosatisfytheoctetruleforeachatom

Distributetheremainingelectronsaspairstothecentralatom

Ifthecentralatomisdeficientinelectrons,completetheoctetforitbyformingdoublebondsorpossiblyatriplebond

OctetRule

Theoctetrulestatesthatthetendencyofatomsinamoleculeistohaveeightelectronsintheiroutershell.

Thereareexceptionstothisrulewherethecentralatommayhavemorethaneightelectrons

Generally,anonmetalinthethirdperiodorhighercanaccommodateasmanyastwelveelectrons,ifitisthecentralatom

Theseelementshaveunfilled“d”subshellsthatcanbeusedforbonding

Resonance(DelocalizedBonding)

StructuresofsomemoleculescanberepresentedbymorethanoneLewisdotformula

IndividualLewisstructuresarecalledcontributingstructures

Individualcontributingstructuresareconnectedbydouble-headedarrows(akaresonancearrows)

Moleculeorionisahybridofthecontributingstructuresanddisplaysdelocalizedbonding

Delocalizedbondingiswhereabondingpairofelectronsisspreadoveranumberofatoms

Someresonancestructurescontributemoretotheoverallstructurethanothers

Determiningwhichstructuresaremorecontributing

Structureswhereallatomshavefilledvalenceshells

Structureswiththegreaternumberofcovalentbonds

Structureswithlesscharges

Formalchargescanhelpdiscernwhichstructureismostlikely(discussedlaterinthissection)

Structuresthatcarryanegativechargeonthemoreelectronegativeatom

ExampleofResonanceStructures:

Curvedarrow–symbolusedtotheredistributionofvalenceelectrons

Alwaysdrawnasnotedinthefigurebelow

HowCurvedArrowsareDrawn:

FormalCharge

Anatom’sformalchargeis:

Totalnumberofvalenceelectrons

Minusallunsharedelectron

Minus½ofitssharedelectrons

Formalchargeshavetosumtotheactualchargeofthespecies

0chargeforamolecule

Ionicchargeforanion

Lewisstructureswiththesmallestformalchargearethemostlikelytooccur

FormalChargevs.OxidationNumber

Formalchargesareusedtoexamineresonancehybridstructures

Oxidationnumbersareusedtomonitorredoxreactions

Formalcharge

Bondingelectronsareassignedequallytotheatoms

Eachatomhashalftheelectronsmakingupthebond

FormalCharge=valencee-–(unbondede-+½bondinge-)

OxidationNumber

Bondingelectronsaretransferredcompletelytothemoreelectronegativeatom

OxidationNumber=valencee-–(unbondede-+bondinge-)

Valence-ShellElectronPairRepulsionModel(VSEPR)

VSEPRpredictstheshapesofmoleculesandionsbyassumingthatthevalenceshellelectronpairsarearrangedasfarfromoneanotheraspossible.

Moleculargeometry–3-Darrangementofatomsthatconstituteamolecule

Shapeofamoleculeisdeterminedbythepositionsofatomicnucleirelativetoeachother

Rulestohelpdiscernelectronpairarrangements

Selectthecentralatom

Placeatomwiththelowestgroupnumberinthecenter

Ifatomssharethesamegroupnumberplacetheatomwiththehigherperiodnumberinthecenter

DrawtheLewisstructure

Determinethenumberofbondingelectronpairsaroundthecentralatom

Determinethenumberofnon-bondingelectronpairs

Multiplebondsarecountedasasingleelectronpair

Arrangetheelectronpairsasfarapartaspossible

Minimizeselectronrepulsions

Addthenumberofbondingandlonepairs

Fromthatnumberandthenumberoflonepairsyoucanusethechartbelowtodeterminethegeometry

Forexample:Ifyouweregivenamoleculewherethecentralatomhad2bondingpairsand1non-bondingpair(totalnumber=3),themolecularshapewouldbebent/angular

ExampleQuestion:DeterminethemolecularshapeofCO2accordingtoVSEPRtheory.

CO2:

Centralatom:C

Chas2bondingpairs,0non-bondingpairs

Rememberthatdoublebondsarecountedasasingleelectronpair

AccordingtoVSEPRmodelthebondsarearrangedlinearly

Bondangle=180˚

Molecularshapeislinear

ExampleQuestion:DeterminethemolecularshapeofCOCl2accordingtoVSEPRtheory.

ExampleofCOCl2:

Centralatom:C

Chas3bondingpairs,0non-bondingpairs

AccordingtoVSEPRmodelthethreegroupsofelectronpairsarearrangedinatrigonalplane

Bondangle=120˚

Molecularshapeistrigonalplanar

EffectofLonePairs

Lonepairsarelessconfinedbecausetheyareheldbyasinglenucleus

Allowsthemtoexertastrongerrepulsiveforcethanabondingpair

Resultsinadecreaseintheanglebetweenbondingpairs

DipoleMomentDipolemoment(µ)-measureofthedegreeofchargeseparation(molecularpolarity)inamolecule

µ=Q*rQ=Charger=distancebetweenthecharges

Polarityofindividualbondswithinamoleculecanbeviewedasvectorquantities

Moleculesthatareperfectlysymmetrichaveazerodipolemoment

ThesemoleculesareconsiderednonpolarMoleculesthatexhibitanyasymmetryinthearrangementofelectronpairswillhavesomedipolemoment

Thesemoleculesareconsideredpolar

ExampleofH2OPolarityVectors:MolecularGeometryandDipoleMomentRelatedness

CHAPTER9–BONDINGTHEORIES

ValenceBondTheory

Valencebondtheoryisanattempttoexplainthecovalentbondfromaquantummechanicalview.

Orbitals(s,p,d,f)ofthesametypehavethesameenergy

Accordingtothetheory,abondformswhentwoatomicorbitalsoverlap

Spaceformedbyoverlappingorbitalshasacapacityfortwoelectrons

Musthaveoppositespins(+½and-½)

Eachorbitalformingthebondhasatleastoneunfilledslottoaccommodatetheelectronbeingshared

Bondstrengthdependsontheattractionofthenucleiforthesharedelectrons

Greaterorbitaloverlap=strongerbond

Overlapdependsontheshapesanddirectionoftheorbitals

HybridOrbitals

Quantummechanicalcalculationsshowthatifspecificcombinationsoforbitalsaremixed,“new”atomicorbitalsareformed

Theseneworbitalsarecalledhybridorbitals

Typesofhybridorbitals

Eachtypehasauniquegeometricarrangement

Hybridorbitalsareusedtodescribebondingthatisobtainedbytakingcombinationsofatomicorbitalsofanisolatedatom

Stepsfordeterminingbondingdescription

WritetheLewisdotformulaforthemolecule

ThenusetheVSEPRtheorytodeterminethearrangementofelectronpairsaroundthecentralatom

Fromthegeometricarrangement,determinethehybridizationtype

Assignvalenceelectronstothehybridorbitalsofthecentralatomoneatatime

Paironlywhennecessary

Formbondstothecentralatombyoverlappingsinglyoccupiedorbitalsofotheratomswiththesinglyoccupiedhybridorbitalsofthecentralatom

MultipleBonds

Orbitalscanoverlaptwoways

Sidetoside

Endtoend

Twotypesofcovalentbonds

Sigmabonds(C-C)

Formedfromanoverlapofoneendoftheorbitaltotheendofanotherorbital

pibonds(C=C)

Formedwhenorbitalsoverlapsidetoside

Createstworegionsofelectrondensity

Oneaboveandonebelow

Doublebondsalwaysconsistofonesigmabondandonepibond

MolecularOrbitalTheory

Asatomsapproacheachotherandtheiratomicorbitalsoverlap,molecularorbitalsareformed

Onlyouter(valence)atomicorbitalsinteractenoughtoformmolecularorbitals

Combiningatomicorbitalstoformmolecularorbitalsinvolvesaddingorsubtractingatomicwavefunctions

Addingwavefunctions

Formsabondingmolecularorbital

Electronchargebetweennucleiisdispersedoveralargerareathaninatomicorbitals

Molecularorbitalshavelowerenergythanatomicorbitals

Reductioninelectronrepulsion

Bondingmolecularorbitalismorestablethanatomicorbital

SubtractingWaveFunctions

Formsaantibondingmolecularorbital

Electronsdonotshieldonenucleifromtheother

Resultsinincreasednucleus-nucleusrepulsion

Antibondingmolecularorbitalshaveahigherenergythanthecorrespondingatomorbitals

Whentheantibondingorbitalisoccupied,themoleculeislessstablethanwhentheorbitalisnotoccupied

MolecularOrbitalsofH2:

CHAPTER10-GASESANDGASLAWS

PropertiesofGases

Flowfreely

Relativelylowdensities

Gasesformhomogenousmixtureswitheachother

Volumeofgaseschangesignificantlywithpressure

Volumesofsolidsandliquidsvolumesarenotgreatlyaffectedbypressure

Volumeofgaseschangessignificantlywithtemperature

Underhightemperaturesgasesexpand

Underlowtemperaturesgasescontract

Pressure

Force(F)-afunctionofthemassofanobjectunderacceleration

F=MassxAcceleration

Pressure(P)-forceexertedperunitareaofsurfacebymoleculesinmotion

A=area

m=mass

a=acceleration

d=density

g=accelerationduetogravity=9.81m/s2

h=heightofcolumn(m)

Pressurehasmanyunits

SIunitisPascal(Pa)=1kg•m-1•sec-2

Atmosphereandtorrarecommonlyused

1atmosphere(atm)=760mmHg=760torr

GasLaws

Thebehaviorofgascanbedescribedbypressure(P),temperature(T),volume(V),andmolaramount(n).Ifyouholdanyofthetwovariablesconstant,itallowsfordeterminationofarelationshipbetweentheothertwo.

Idealgas–gasthatexhibitslinearrelationshipsamongpressure,temperature,volume,andmolaramount

Idealgasesdon’tactuallyexist

Butsimplegasesbehaveideallyundernormaltemperaturesandpressures

Molargasvolume(Vm)–volumeofonemoleofgas

Volumesofgasesareoftencomparedatstandardtemperatureandpressure(STP)

StandardTemperature=0˚C(273K)

StandardPressure=1atm

VmatSTP=22.4L/mol

BoylesLaw

Volumeofasampleofgasataconstanttemperatureisinverselyrelatedtotheappliedpressure

P1V1=P2V2or

CharlesLaw

Volumeofasampleofgasatconstantpressureisdirectlyproportionaltotheabsolutetemperature

Avogadro’sLaw

Equalvolumesofdifferentgasesatthesametemperatureandpressurecontainequalnumberofparticles

CombinedGasLaw

ForwhenP,V,andTarechanging

IdealGasLaw

PV=nRT

Ristheuniversalgasconstant

R=0.082058L•atm•mol-1•K-1=8.3145J•mol-1•K-

1

Aslongasyouknowthreeofthevariablesyoucanmanipulatetheidealgaslawtosolveforthefourth

MolarMassfromIdealGasLaw

Density

LawofPartialPressures

Kinetic-MolecularTheoryofGases

Amodelbasedonactionsofindividualatoms

Gasesconsistofparticlesinconstantmotion

Pressurederivedfrombombardmentwithcontainer

Kineticenergyformula:Ek=½mv2

PostulatesofKineticTheory

Volumeofparticlesisnegligible

Particlesareinconstantmotion

Noinherentattractiveorrepulsiveforces

Theaveragekineticenergyofacollectionofparticlesisproportionaltothetemperature(K)

MolecularMotioninGases

Diffusion–transferofgasthroughspaceoranothergasovertime

Effusion–transferofagasfromaregionofhighpressuretoaregionoflowpressure

GrahamsLawofEffusion

CHAPTER11-THERMOCHEMISTRY

Thermochemistry

Inchemicalreactionswhenevermatterchangescomposition,itsenergycontentchangesaswell

Insomereactionstheenergycontainedinthereactantsishigherthantheenergycontainedintheproducts

Theexcessenergyisreleasedasheat

Inotherreactionstheenergycontainedinthereactantsislowerthantheenergycontainedintheproducts

Inthesereactions,energy(heat)mustbeaddedbeforethereactioncanproceed

Physicalchangesalsoinvolveachangeinenergy

Thermodynamics-scienceoftherelationshipbetweenheatandotherformsofenergy

Thermochemistry-studyofthequantityofheatabsorbedorexudedbychemicalreactions

Energy

Energyisthepotentialorcapacitytodowork.Energyisapropertyofmatterandcomesinmanyforms.

Formsofenergy

Radiantenergy-electromagneticradiation

Thermalenergy-associatedwithrandommotionofamoleculeoratom

Chemicalenergy-energystoredwithinthestructurallimitsofamoleculeoratom

ConceptsofEnergy

Kineticenergy(Ek)–energypossessedbyanobjectduetoitsmotion

Ek=½mv2

Potentialenergy(Ep)–energystoredinmatterbecauseofitspositionorlocation

Ep=mgh

Internalenergy(EiorUi)–energyassociatedwiththerandomdisorderedmotionofmolecules

Ei=Ek+Ep

UnitsofEnergy

SIunitofenergyistheJoule(J)=kg•m2/s2

Calorie(cal)-amountofheatrequiredtoraisethetemperatureofonegramofwaterbyonedegreeCelsius

1cal=4.181J

Whenreactantsinteracttoformproductsandtheproductsareallowedtoreturntothestartingtemperature,theInternalEnergy(E)haschanged

∆E=changeinenergy

∆isthesymbolforchange

∆=finalvalue–initialvalue

∆E=Efinal-Einitial=Eproducts-Ereactants

Ifenergyislosttothesurroundings

Efinal<Einitial

∆E<0

Ifenergyisgainedfromthesurroundings

Efinal>Einitial

∆E>0

HeatofReaction

Inchemicalreactions,heatiseithertransferredfromthe“system”toits“surroundings,”orviceversa.

Thermodynamicsystem-quantityofmatterorthespaceunderthermodynamicstudy

Surroundings-everythinginthevicinityofthethermodynamicsystemthatinteractswiththesystem

Heat(q)-energythatflowsintooroutofasystembecauseofadifferenceintemperaturebetweenthesystemanditssurroundings

Heatflowsfromaregionofhighertemperaturetoaregionoflowertemperature

Oncetemperaturesequalize,heatflowstops

Whenheatisreleasedfromthesystemtothesurrounding

q<0

Reactioniscalledanexothermicreaction

Whenheatisabsorbedfromthesurroundingbythesystem

q>0

Reactioniscalledanendothermicreaction

Heatofreaction-thevalueof“q”requiredtoreturnasystemtoagiventemperaturewhenthereactiongoestocompletion

Work

Internalenergyisspecificallydefinedasthecapacityofasystemtodowork.

Work–energytransferredwhenanobjectismovedbyaforce

w=-P∆V

∆E=qp+w

∆E=qp+-P∆V

qp=∆E+P∆V

qp-heatabsorbedfromthesurroundingsbythesystem

∆E-changeininternalenergy

∆V-changeinvolume

P–pressure

EnthalpyandEnthalpyChange

Enthalpy(H)-anextensivepropertyofasubstancethatisusedtoobtaintheheatabsorbedorexudedinachemicalreaction

H=E+PV

Enthalpyisastatefunction

Propertyofasystemthatdependsonlyonitsstateatthemomentandisindependentofanyhistoryofthesystem

Enthalpyisrepresentativeoftheheatenergytiedupinchemicalbonds

Changeinenthalpy(∆H)-heataddedorlostbythesystem,underconstantpressure

∆H=∆E+P∆V

∆H=qp

Changeinenthalpyisalsocalledtheenthalpyofreaction

∆Hrxn=H(products)–H(reactants)

Ifthesystemhashigherenthalpyattheendofthereaction

Itabsorbedheatfromthesurroundings

Itisanendothermicreaction

Hfinal>Hinitial

∆Hispositive(+∆H)

Ifthesystemhaslowerenthalpyattheendofthereaction

Itexudedheattothesurroundings

Itisanexothermicreaction

Hfinal<Hinitial

∆Hisnegative(-∆H)

ThermochemicalEquation

Thermochemicalequationsarechemicalreactionequationswiththeenthalpyofreaction(∆Hrxn)writtendirectlyaftertheequation.

Exampleofathermochemicalequation

2H2(g)+O2(g)→2H2O(l)∆Hrxn=-571.6kJ

Thenegativevaluefor∆Hrxnistellingyouthatheatislosttothesurrounding

Alsothattheequationisexothermic

Rulesformanipulatingthermochemicalequations

Ifthethermochemicalequationismultipliedbysomefactor,thevalueof∆Hforthenewequationisequaltothe∆Hintheoriginalequationmultipliedbythatfactor

Ifthechemicalequationisreversed,thesignof∆Hmustbereversed

Example,ifyouweretoreversethedirectionoftheequationmentionedaboveyouwouldget:

2H2O(l)→2H2(g)+O2(g)∆Hrxn=+571.6kJ

MeasuringHeatsofReaction

Heatcapacity–amountofheatrequiredtoraisethetemperatureofanobjectorsubstance

Variesbetweensubstances

Molarheatcapacity(C)–amountofheatrequiredtoraisethetemperatureofonemoleofasubstancebyonedegreeCelsius

q=nC∆T

∆T=Tfinal-Tinitial

Specificheatcapacity(S)–amountofheatrequiredtoraisethetemperatureofonegramofasubstancebyonedegreeCelsius

q=mS∆T

∆T=Tfinal-Tinitial

UnitsforS:J/g•˚C

m=gramsofasample

Hess’sLawofHeatSummation

Forachemicalequationthatcanbewrittenasthesumoftwoormoresteps,theenthalpychangesfortheindividualstepscanbesummed(added)uptodeterminetheenthalpychangefortheoverallequation

Forcoupledreactions,theindividualenthalpychangescanbesummeduptodeterminetheenthalpychangefortheoverallreaction

Hess’sLawExampleQuestion:Whatisthestandardenthalpyofreactionforthereductionofiron(II)oxidebycarbonmonoxide?FeO(s)+CO(g)→Fe(s)+CO2(g)

GivenInformation:

Equation1:3Fe2O3(s)+CO(g)→2Fe3O4(s)+CO2(g)ΔH=-48.26kJ

Equation2:Fe2O3(s)+3CO(g)→2Fe(s)+3CO2(g)ΔH=-23.44kJ

Equation3:Fe3O4(s)+CO(g)→3FeO(s)+CO2(g)ΔH=+21.79kJ

Changeshavetomadetotheaboveequationstoequaltheequationinthequestion

Reverseequation3andmultiplyitbytwo

PutsFeOonthereactantsideandmoves2Fe3O4totheproducts

Reverseequation1

PutsFe3O4onoppositesidetocancelwiththereverseofequation3

Multiplyequation2bythree

Gives3Fe2O3onthereactantsthatwillbeusedtocancel

Newequationsafterchanges

Equation1:2Fe3O4(s)+CO2(g)→3Fe2O3(s)+CO(g)ΔH=+48.26kJ

Equation2:3Fe2O3(s)+9CO(g)→6Fe(s)+9CO2(g)ΔH=-70.32kJ

Equation3:6FeO(s)+2CO2(g)→2Fe3O4(s)+2CO(g)ΔH=-43.58kJ

Summingthethreeequationsgives

6FeO(s)+6CO(g)→6Fe(s)+6CO2(g)ΔH=-65.64kJ

Dividingbysixgivestheequationinthequestionandthefinalanswer

FeO(s)+CO(g)→Fe(s)+CO2(g)ΔH=-10.94kJ

StandardEnthalpiesofFormation

Standardstatereferstothestandardthermodynamicconditions

Pressure-1atm(760mmHg)

Temperature-25˚C(298K)

Enthalpychangeforareactionwherereactantsareintheirstandardstatesiscalledthe“StandardHeatofReaction”

ΔH˚rxn

Standardenthalpyofformationofasubstance-enthalpychangefortheformationofonemoleofasubstanceinitsstandardstatefromitscomponentelementsintheirstandardstates

Standardenthalpyofformationfora“pure”element(C,Fe,O,N,etc.)initsstandardstateiszero

LawofSummationofHeatsofFormation

Thestandardheatofreaction(∆H˚rxn)isequaltothetotalformationenergyoftheproductsminusthetotalformationenergyofthereactants

mandnarecoefficientsofthesubstancesinthechemicalequation

GibbsFreeEnergyGibbsfreeenergycanbeusedtodeterminethedirectionofthechemicalreactionundergivenconditions .

∆G=∆H-T∆Sor∆G=Gproducts-Greactants

G=Gibbsfreeenergy(J/mol)

H=enthalpy(J/mol)-totalenergycontentofasystem

S=entropy(J/K*mol)-measureofdisorderorrandomness(howenergyisdispersed)

T=Temperature(K)

AsTincreasessodoesS

+∆Gmeansenergymustbeputintothesystem

Indicatesthataprocessisnonspontaneousorendergonic

Indicatesthatthepositionoftheequilibriumforareactionfavorstheproducts

-∆Gmeansenergyisreleasedbythesystem

Indicatesthataprocessisspontaneousorexergonic

Indicatesthatthepositionoftheequilibriumforareactionfavorsthereactants

∆G=0indicatesthatthesystemisatequilibrium

Important:∆Gonlyindicatesifaprocessoccursspontaneouslyornot,butdoesnotindicateanythingabouthowfastaprocessoccurs.

CHAPTER12:SOLUTIONS

Solutions

Solutionsarecomposedofasoluteandasolvent

Solutionsarehomogeneousmixtures

Solutesareminorcomponentsinasolution(presentinsmalleramounts)

Solventsaresubstancesinwhichasoluteisdissolved

Solutioncompositionisexpressedby:

Masspercent

Molefraction

Xsolute

Xsolute=nsolute/ntotal

Molarity

Molality

ConversionbetweenMolarityandMolality

Densitymustbeknowntoconvertfrommolaritytomolalitydirectly.

ExampleQuestion:Whatismolalityof2.00MNaCl(aq)solutionwithadensityof1.08g/mL?

Determinethemassof2.00molofNaCl

2.00molx(58.5g/mol)=117gNaCl

Assumeyouhave1.000L(1000mL)ofthe2.00MNaClsolution

Youcanassumeanyamountifitisnotexplicitlystatedinthequestion

Hint:itisbesttoassumeanamountthatiseasytoworkwith

Toconvertmolaritytomolalityassume1.000Lofsolution

Toconvertmolalitytomolarityassume1.000kgofsolvent

Usethedensitygivenintheproblemtodeterminethetotalmassofthesolution

1000mLx(1.08g/mL)=1080gtotalmass

Determinethemassofthesolvent

Earlierwecalculatedthatwehad117gNaClandthetotalmassofthesolutionwas1080g

So,todeterminethemassofthesolventwewillsimplysubtractthedifference

1080gofsolution–117gNaCl=963gsolvent(0.963kgsolvent)

Finally,usetheformulaformolalitytodeterminetheanswer

Concentratedvs.DiluteSolutions

Concentratedsolution–asolutionthatcontainsahighamountofsolute

Moresoluteparticlesperunitvolume

Dilutesolution–asolutionthatcontainsalowamountofsolute

Fewersoluteparticlesperunitvolume

Saturatedsolution-asolutionthatcontainsthemaximumamountofsolutethatcanbedissolvedbythesolvent

Dilutions

Extrasolventisaddedtoasolutiontodiluteit

Theamountofsoluteinthesolutionremainsthesame

Usethefollowingformulatosolvedilutionproblems:

M1V1=M2V2

M1–istheconcentrationofstocksolution

V1–isthevolumeofstocksolution

M2–istheconcentrationofthefinalsolution

V2–isthevolumeofthefinalsolution

Henry’sLaw

FormulatedbyWilliamHenryin1803,itstates:"Ataconstanttemperature,theamountofagivengasthatdissolvesinagiventypeandvolumeofliquidisdirectlyproportionaltothepartialpressureofthatgasinequilibriumwiththatliquid."

C=kxPgas

C–solubilityofagasatafixedtemperatureinaparticularsolvent

k-Henry’sLawconstant

Pgas–partialpressureofthegas

ColligativeProperties

Colligativepropertiesrefertopropertiesofsolutionsthatdependupontheratioofthenumberofsoluteparticlestothenumberofsolventmoleculesinasolution.Thesepropertiesdon’tdependonthetypeofchemicalspeciespresent.

Commoncolligativeproperties

Vaporpressurelowering

Freezingpointdepression

Boilingpointelevation

Osmoticpressure(discussedindetailinitsownsection)

VaporPressureLowering

Raoult’sLawsaysthatifyouaddanonvolatilesolutetoasolvent,youwillcausethevaporpressureofthesolutetobelower

Raoult’sLawequation:

Psolution=XsolventPosolvent

Psolution-vaporpressureofsolution

Xsolvent-molefractionofsolventinsolution

Posolvent-vaporpressureofpuresolvent

BecauseXsolventisamolefraction(anumberbetween0and1),PsolutionisalwayslowerthanPosolvent

FreezingPointDepression

Propertybasedontheobservationthatfreezingpointsofsolutionsarealllowerthanthatofthepuresolventandisdirectlyproportionaltothemolalityofthesolute

Formula:∆Tf=Tf(solvent)-Tf(solution)=Kfxm

∆Tf-freezingpointdepression

Tf(solvent)–freezingpointofthesolvent

Tf(solution)–freezingpointofthesolution

Kf=freezingpointdepressionconstant

m–molality

BoilingPointElevation

Propertybasedontheobservationthattheboilingpointofasolventishigherwhenanothercompoundisadded(i.e.solutionhasahigherboilingpointthanapuresolvent)

Formula:∆Tb=Kbxm

∆Tb–boilingpointelevation

Kb=boilingpointelevationconstant

m–molality

OsmoticPressure

Semipermeablemembranesstopsolutemoleculesorionsfrompassingthroughbutallowpassageofsolventmolecules.Solventmoleculessuchaswaterwillgothroughmembranestodiluteasolutionunlessapressureequaltotheosmoticpressureisappliedtostoptheflow.So,osmoticpressureisdefinedastheminimumpressurewhichneedstobeappliedtoasolutiontopreventtheinwardflowofwateracrossasemipermeablemembrane.

Hypertonic-referstoasolutionthathashigherosmoticpressurethanaparticularfluid(e.g.intracellularfluid)

Isotonic-referstoasolutionthathasthesameosmoticpressurethanaparticularfluid(e.g.intracellularfluid)

Hypotonic-referstoasolutionthathasthelowerosmoticpressurethanaparticularfluid(e.g.intracellularfluid)

Osmoticpressure( )formula

V=nRTor =MRT

n=molesofsolute

V=volumeofsolution(L)

R=gasconstant(0.08206L · atm/mol ·K)

T=temperatureinKelvin

M=molarity

HydrophobicEffectandAmphiphilicMoleculesThehydrophobiceffectisthetendencyofnonpolarsubstancestoaggregateinaqueoussolutionandexcludewatermolecules.Amphiphilicmoleculeshavebothhydrophobicandhydrophilicparts.

Hydrophobic–water“hating”Incontrast,hydrophilic–water“loving”

AmphiphilicMoleculesinWater

Nonpolartails(hydrophobicportion)pointawayfromwaterPolarheads(hydrophilicportion)areexposedtowater

DifferentamphipathicmoleculesaggregateindifferentwaysbasedonthenumberoftailsandsizeofthepolarheadgroupMicellesformwhenthereisonly1tailandtakesphericalforminaqueoussolutions

CHAPTER13–CHEMICALKINETICS

Introduction

Reactionsoccuratdifferentrates

Someareveryquick,someareveryslow,andmanyfallsomewhereinbetween

Knowingtherateofareactionhelpschemistsplanoutexperimentsandplanreactionsaccordingly

Ifyouunderstandwhatcontributestorate,youcanexertsomecontroloverareaction

Chemicalequations(e.g.,Al2O3→Al+O2)don’ttellyouanythingabouthowfastthereactionoccurs

Somereactionsoccurinaseriesofsmallerstepsthatleadtothefinalproduct

ReactionRates

Generally,ratesaredefinedasthechangeofsomethingdividedbychangeintime.Thisistrueofreactionratesaswell.

Rateofareactioncanbewrittenwithrespecttoanycompoundinthatreaction

But,therecanonlybeonenumericalvalueforarateofreaction

Ifyouplotaverageratedataasafunctionoftime,youwillseethatthereactionrateconstantlychanges(considerthegraphbelow)

RateDataforaReaction:

Asyoumightnotice,ratedependsontheconcentrationofthereactants

Sincetherateofareactioniseffectedbytheconcentrationofthereactantswecanwritemathematicalrelationshipslinkingtheconcentrationofreactantswithhowfastthereactionoccurs(i.e.wecanwriteratelaws)

GeneralReactionRates

Considerthegeneralchemicalequation:aA+bB→cC+dD

Rateforthisreactionwouldbedefinedas:

Asimpleratelawexample:

Considerthedecompositionreactionwhere:A products

Ifthereversereactionisnegligible,thentheratelawis:Rate=k[A]n

kiscalledtherateconstant

niscalledthereactionorder

ReactionOrders

Reactionorder(denotedas“n”)determineshowtheratedependsontheconcentrationofthereactant

n=0,zeroorder,rateisindependentof[A]

n=1,firstorder,rateisdirectlyproportionalto[A]

n=2,secondorder,rateisproportionaltothesquareof[A]

Eachorderresultsinadifferenttypeofcurvewhengraphed

Important:Youcanonlydeterminereactionordersthroughanexperiment

Reactionordersarenotrelatedtothestoichiometryofareaction

StepsforFindingRateLaw

Picktwosolutionswhereonereactantstayssame,butanotherchanges

Writetheratelawforbothusingasmuchinformationasyouhave

Formaratiofromthetwoandsolveforanorder

Repeatthe3stepsaboveforanotherpairofsolutions

Useanyreactiontogetthevalueofk

AnExampleProblem

Imagineweareconsideringthegeneralreaction:A+B→products

Andthatwedeterminedthefollowinginformationfromanexperiment:

Lookatexperiments1and2

Fromexperiment2to1,weseethattheconcentrationofAdoubles(whileBisheldconstant)andtheratealsodoubles

DoublingoftheratewithadoublingoftheconcentrationshowsthatthereactionisfirstorderwithrespecttoA

Nextlookatexperiments1and3

ConcentrationofBishalved(whileAisheldconstant)

WhenBishalved,theoverallratedropsbyafactorof4(whichisthesquareof2)

ThisshowsthereactionissecondorderwithrespecttoB

Theratelawwouldbewrittenas:rate=k[A][B]2

Youcanuseanyreactiontogetthevalueofk(Iwilluseexperiment1)

Rate=k[A][B]2

1.60mMmin-1=k(4.0mM)(6.0mM)2

k=0.011mM-2min-2

IntegratedRateLawandHalfLifeFormulas

Notethattheintegratedratelawequationsareintheformy=mx+b

y=mx+bistheformulaforastraightline

So,theplotofln[A]vs.timeforthereactionswillyieldastraightline

For2ndorder,half-lifedependsoninitialconcentration

Asconcentrationdecreases,thehalf-lifeincreases

Half-lifeforzeroorderreactionsdependsonconcentrationaswell

However,noticethatthehalf-lifedoesn’tdependonreactantconcentrationforthe1storderreactions

Half-lifefora1storderreactionisconstant

TemperatureandRateGenerally,ratesofreactionaresensitivetotemperature

Rate=k[A]n,sowheredowefactorintemperature?ItisreflectedintheconstantkGenerally,increasingtemperatureincreasesk

ChemistryofCatalysisCatalystsdonotchangethedirectionofachemicalreactionandtheyhavenoeffectonequilibrium!

Functionbyloweringtheactivationenergy,whichspeedsupthereaction

Asthereactionprogresses;reactantsbecomeproducts

Depictedasareactioncoordinatediagram

ReactionCoordinateDiagram:

Progressofthereactionisindicatedonthex-axis

Freeenergy(G)isindicatedonthey-axis

Reactantspassthroughthetransitionstate(‡)andbecomeproducts

Enzymesincreasethereactionratebybindingtightlytothetransitionstateandstabilizingit

Spontaneousvs.Non-spontaneousReactionsSpontaneousifΔGrxnnegative

GeneralSpontaneousReactionDiagram:

Non-spontaneousifΔGrxnpositive

GeneralNon-spontaneousReactionDiagram:

Enzymes(catalysts)lowertheenergybarrierMakeiteasiertoreachthetransitionstate

CHAPTER14–CHEMICALEQUILIBRIUM

WhatisEquilibrium?

Asasystemisapproachingequilibrium,boththeforwardandreversereactionsareoccurringatdifferentrates

Chemicalequilibriumisestablishedwhenareactionanditsreversereactionoccuratthesamerate

Onceequilibriumisestablished,theamountofboththereactantandproductremainsconstant

Inasystematequilibrium,boththeforwardandreversereactionsarerunningsimultaneouslysowewritethechemicalequationforthereactionwithadoublearrow

Example:

EquilibriumConstant

Considerthereaction:

Ratelawfortheforwardreactionwouldbe:rate=kf[N2O4]

Ratelawforthereversereactionwouldbe:rate=kr[NO2]2

Atequilibriumthetworateswouldbethesamesowecanrearrangetheequationstoget:

Keq(akaKc)istheequilibriumconstant

Ingeneral,thereaction:

Resultsintheequilibriumexpression:

Equilibriumcanbereachedfromeithertheforwardorreversedirection

Kc,thefinalratioof[NO2]2to[N2O4],willreachaconstantnomatterwhattheinitialconcentrationsofNO2andN2O4

are(aslongastimeisheldconstantbetweenthem)

Alsonotethattheequilibriumconstantofareactioninthereversereactionisthereciprocaloftheequilibriumconstantoftheforwardreaction

IfK>>1,thereactionissaidtobeproduct-favored

Productspredominateatequilibrium

IfK<<1,thereactionissaidtobereactant-favored

Reactantspredominateatequilibrium

Ifareactionconsistsofmanyindividualsteps,youcanaddtheequilibriumconstantsfortheindividualstepstodeterminetheequilibriumconstantfortheentirereaction

Pressureisproportionaltoconcentrationforgases,becauseofthis,theequilibriumexpressioncanalsobewrittenintermsofpartialpressures(insteadofconcentration)

KpandKcarerelatedtooneanotherbytheequation:Kp=Kc(RT)∆n

∆n=(molesofgaseousproduct)–(molesofgaseousreactant)

HomogeneousandHeterogeneousEquilibrium

Ahomogeneousequilibriumisanequilibriumwhereallreagentsandproductsarefoundinthesamephase(solid,liquid,orgas).Aheterogeneousequilibriumisanequilibriumwheretheyareindifferentphases.

Concentrationsofliquidsandsolidscanbeobtainedbythefollowing:

Concentrationofsolidsandliquidsarenotusedtoformanequilibriumexpression

Considerthereaction:

Theequilibriumconstantforthereactionwouldbe:

Kc=[Pb2+][Cl−]2

ReactionQuotient(Q)

TocalculateQ,youhavetosubstitutetheinitialconcentrationsofreactantsandproductsintotheequilibriumexpression

Qgivesthesameratioastheequilibriumexpressionbutforasystemthatisnotatequilibrium

IfQ=K,thesystemisatequilibrium

IfQ>K,thereismoreproduct,andtheequilibriumshiftstothereactants

IfQ<K,therearemorereactants,andtheequilibriumshiftstotheproducts

TheshiftingofequilibriumisLeChâtelier’sPrinciple

Essentiallytheprinciplestatesthatequilibriumpositionshiftstocounteracttheeffectofadisturbance(changeintemperature,concentration,etc.)

CHAPTER15–ACIDBASEEQUILIBRIUM

DefinitionsandConventions

Acid-basereactionsareatypeofchemicalprocesstypifiedbytheexchangeofoneormorehydrogenions(i.e.exchange/transferofaproton).

Arrheniusdefinition

Acid–substancethatproducesH+ionsinaqueoussolution

WenowknowthatH+reactsimmediatelywithawatermoleculetoproduceahydroniumion(H3O+)

Base–substancethatproducesOH-ionsinaqueoussolution

Bronsted-Lowrydefinition

Acid–protondonor

Base–protonacceptor

Bronsted-Lowrydefinitiondoesnotrequirewaterasareactant

Conjugateacidsandbases

Conjugatebase–speciesthatisformedwhenanaciddonatesaprotontoabase

Conjugateacid–speciesthatisformedwhenabaseacceptsaprotonfromanacid

Conjugateacid-basepair–pairofmoleculesorionsthatcanbeinterconvertedthroughthetransferofaproton

Curvedarrowsareusedtoshowtheflowofelectronsinanacid-basereaction

NeutralizationisthereactionofanH+(H3O+)ionfromtheacidandtheOH-ionfromthebasetoformwater,H2O

Neutralizationreactionisexothermicandreleasesapproximately56kJpermoleofacidandbase

Determiningacidic,basic,andneutralfromconcentrationofH3O+

andOH-

Neutral:[H3O+]=[OH-]

Acidic:[H3O+]>[OH-]

Basic:[H3O+]<[OH-]

StrengthsofAcidsandBases

Strengthofanacidisexpressedbyanequilibriumconstant

Equilibriumexpressionforthedissociationofanunchargedacid(HA)

Ka,theaciddissociationconstant,isgivenby:

Thisisbecausetheconcentrationofwaterishigh,anddoesnotsignificantlychangeduringthereaction,soitsvalueisabsorbedintotheconstant

Thestrongertheacid,thelargertheKa,andthemoreitwilldissociateinsolution

Strongacidscompletelydissociateintoionsinwater

StrongacidsareHI,HBr,HClO4,HCl,HClO3,H2SO4,andHNO3

Theirconjugatebasesareweak

Weakacidsonlypartiallydissociateintoionsinwater

Polyproticacidsareacidsthatarecapableoflosingmorethanasingleprotonpermoleculeduringanacid-basereaction

Phosphoricacidisaweakacidthatnormallyonlylosesoneprotonbutitwillloseallthreewhenreactedwithastrong

baseathightemperatures

IfthedifferencebetweentheKaforthefirstdissociationandsubsequentKavaluesis103ormore,thepHgenerallydependsonlyonthefirstdissociation

Inanyacid-basereaction,theequilibriumfavorsthereactionthatmovestheprotontothestrongerbase

ThemorepolartheH-Xbondand/ortheweakertheH-Xbond,themoreacidicthecompound

Strongbase–abasethatispresentalmostentirelyasions(oneoftheionsisOH-)

StrongbasesareNaOH,KOH,LiOH,RbOH,CsOH,Ca(OH)2,Ba(OH)2,andSr(OH)2

Weakbase–abasethatonlypartiallyionizesinwater

Thegeneralweakbasereactioniswrittenas:

Theequilibriumconstantexpressionforthisreactionis:

Kbiscalledthebase-dissociationconstant

KaandKbcanberelatedtooneanotherusingthefollowingformula:

KaxKb=Kw

Kwistheionizationconstantforwaterat25˚C

Kforwateris: or=1.0x10-14

FindingConcentrationofSpeciesinSolutionfromKa

Given:0.10MHNO2(nitrousacid),Ka=4.5x10-4

Setupatabletohelpyoukeeptrackofwhatishappeningduringthereaction

Someofthereactantwillbecomeproduct,thatiswhythechangeinconcentrationisnegativex

Weareformingsomeamountofproductinthisreactionsothechangeinconcentrationispositivex

Wenowneedtosolveforx,firstsetuptheKaequation

Thesimpleapproach:

ItisacceptedthataslongasX<5%of[HA],where[HA]=concentrationoftheacid,youcanassumexisnegligibleandthat(0.10-x)=0.10,makingtheKaequation:

Theexactapproach(quadraticformula):

However,ifyoucan’tassumexisgoingtobesmallerthan5%youhavetosetuptheexactformula

Thequadraticequationis:ax2+bx+c=0

→x2+4.5x10-4x–4.5x10-5=0

a=1

b=4.5x10-4

c=-4.5x10-5

Thequadraticformula:

Tosolve,substituteinthevaluesfora,b,andc

x=6.5x10-3

Alwaysuseonlythepositiveroot,thenegativerootdoesnotmakesenseinthecontextofthesesortofproblems

Ifyoucomparetheanswerfrombothapproaches(6.7x10-3vs.6.5x10-3)youcanseethattheanswersareprettymuch

thesame

However,rememberthatyoucanonlyusethesimpleapproachifX<5%of[HA]

Sincewefoundx,weonlyneedtosubstitutethevalueintothe“EquilibriumAmount”sectionofthetablewesetupearliertofindtheconcentrationofspeciesinsolution

[HNO2]=(0.10M–x)=(0.10M–6.5x10-3)=0.0935M

[H+]=x=6.5x10-3M

[NO2-]=x=6.5x10-3M

pHandpOH

pHisdefinedasthenegative,base-10logarithmofthehydroniumionconcentration

pH=-log[H3O+]→[H3O+]=10-pH

Inpurewater:

Kw=[H3O+][OH–]=1.0x10-14

Becauseinpurewater[H3O+]=[OH-];

[H3O+]=(1.0 10-14)1/2=1.0x10-7

pH=-log[1.0x10-7]=7.00

7.00isconsideredneutralpH

Anacidhasahigher[H3O+]thanpurewater

pHis<7

Abasehasalower[H3O+]thanpurewater

pHis>7

pHScalewithCommonSubstances:

pinpHisacluetotakethenegativelogofthequantity,thisistrueforpOHandpKw:

pOH=-log[OH-]→[OH-]=10-pOH

pKw=-log(Kw)→Kw=10-pKw

pKaandTrends

Ka=10-pka

pKa=-log(Ka)

LowerthepKa,thestrongertheacid

HigherthepKa,theweakertheacid

LowerthepKa,theweakertheconjugatebase

HigherthepKa,thestrongertheconjugatebase

Equilibriumfavorsthesideoftheweakestacidandweakestbase

EquilibriumfavorsthesidewiththehighestpKa

Thus,pKacanbeusedtopredictinwhichdirectionequilibriumlies

PercentIonizationFormulas

ReactionsofAnionsandCationswithWater

Anionsarebases

TheycanreactwithwaterinahydrolysisreactiontoformOH–

andtheconjugateacid:

Cationswithacidicprotons(likeNH4+)lowerthepHofasolution

becausetheyreleaseH+ionsinsolution

MostmetalcationsthatarehydratedinsolutionalsolowerthepHofthesolution

ActbyassociatingwithH2OandmakingitreleaseH+

Attractionbetweennonbondingelectronsonoxygenandthemetalcausesashiftoftheelectrondensityinwater

ThismakestheO-Hbondmorepolarandthewatermoreacidic

Greaterchargeandsmallersizemakeacationmoreacidic

EffectsofCationsandAnions

AnanionthatistheconjugatebaseofastrongacidwillnotaffectthepH

AnanionthatistheconjugatebaseofaweakacidwillincreasethepH

AcationthatistheconjugateacidofaweakbasewilldecreasethepH

CationsofastrongArrheniusbasewillnotaffectthepH

OthermetalionswillcauseadecreaseinpH

Whenasolutioncontainsboththeconjugatebaseofaweakacidandtheconjugateacidofaweakbase,theeffectonpHdependsontheKaandKbvalues

CHAPTER16–SOLUBILITYEQUILIBRIUM

WhatisSolubilityEquilibrium?

Ifan“insoluble”orslightlysolublematerialisplacedinwateranequilibriumformsbetweentheundissolvedsolidsandionicspeciesinsolutions

Solidscontinuetodissolve,whileion-pairscontinuetoformsolids

Therateofdissolutionisequaltotherateofprecipitation

Considerthereaction:AgCl(s)⇌ Ag+(aq)+Cl-(aq)

K=

However,rememberthatsinceAgClisapuresoliditisn’tconsideredinKandthustheequationcanberewrittenas:Ksp=[Ag+][Cl-]

SolubilityProduct(Ksp)

Generalexpression:MmXn(s)⇄ mMn+(aq)+nXm-(aq)

Solubilityproductforthegeneralexpression:Ksp=[Mn+]m[Xm-]n

Exampleofhowtofindsolubility(s)fromKsp:

AgCl(s)⇌ Ag+(aq)+Cl-(aq)

Ksp=[Ag+][Cl-]=1.6x10-10

IfsisthesolubilityofAgCl,then:

[Ag+]=sand[Cl-]=s

Ksp=(s)(s)=s2=1.6x10-10

s=1.3x10-5mol/L

Anotherexample:

Ag3PO4(s)⇌ 3Ag+(aq)+PO43-(aq)

Ksp=[Ag+]3[PO43-]=1.8x10-18

IfthesolubilityofAg3PO4issmol/L,then:

Ksp=(3s)3(s)=27s4=1.8x10-18

s=1.6x10-5mol/L

FactorsAffectingSolubility

Temperature

Generally,solubilityincreaseswithtemperature

Commonioneffect

Commonionsreducesolubility

Considerthefollowingsolubilityequilibrium:

AgCl(s)⇌ Ag+(aq)+Cl-(aq);Ksp=1.6x10-10

ThesolubilityofAgClis1.3x10-5mol/Lat25˚C.

IfNaClisadded,equilibriumshiftsleftduetoincreasein[Cl-]andsomeAgClwillprecipitateout

Forexample,if[Cl-]=1.0x10-2M,

SolubilityofAgCl=(1.6x10-10)/(1.0x10-2)=1.6x10-8mol/L

pHofsolution

pHaffectsthesolubilityofioniccompoundsinwhichtheanionsareconjugatebasesofweakacids

Considerthefollowingequilibrium:

Ag3PO4(s)⇌ 3Ag+(aq)+PO43-(aq);

IfHNO3isadded,thefollowingreactionoccurs:

H3O+(aq)+PO43-(aq)⇌ HPO4

2-(aq)+H2O

ThisreactionreducesPO43—insolution,causingmoresolid

Ag3PO4todissolve

Formationofcomplexion

Formationofcomplexionincreasessolubility

Manytransitionmetalsionshavestrongaffinityforligandstoformcomplexions

Ligandsaremoleculessuchas:H2O,NH3andCO,oranions,suchasF-,CN-andS2O3

2-

Complexionsaresoluble

Sotheformationofcomplexionsincreasessolubilityofslightlysolubleioniccompounds

PredictingFormationofPrecipitate

Qsp=Ksp

Saturatedsolution,butnoprecipitate

Qsp>Ksp

Saturatedsolution,withprecipitate

Qsp<Ksp

Unsaturatedsolution

QspisionproductexpressedinthesamewayasKspforaparticularsystem

ExampleQuestion:20.0mLof0.025MPb(NO3)2isaddedto30.0mLof0.10MNaCl.PredictifprecipitateofPbCl2willform.Given:KspforPbCl2=1.6x10-5

[Pb2+]=(20.0mLx0.025M)/(50.0mL)=0.010M

[Cl-]=(30.0mLx0.10M)/(50.0mL)=0.060M

Qsp=[Pb2+][Cl-]2=(0.010M)(0.060M)2=3.6x10-5

Qsp>Ksp,soPbCl2willprecipitate

CHAPTER17–ELECTROCHEMISTRY

WhatisElectrochemistry?

Electrochemistryisabranchofchemistryconcernedwiththestudyoftherelationshipbetweenelectronflowandredoxreactions.

Review:

Oxidation-reductionreactions(akaredoxreactions)–reactionsthatinvolveapartialorcompletetransferofelectronsfromonereactanttoanother

Oxidation=lossofelectrons

Reduction=gainofelectrons

Trickforrememberingwhichiswhich-OILRIG

OIL-OxidationIsLosingelectrons

RIG-ReductionIsGainingelectrons

Oxidationandreductionalwaysoccursimultaneously

OxidationNumber=valencee-–(unbondede-+bondinge-)

Oxidizingagent–speciesthatoxidizesanotherspecies

Itisitselfreduced–gainselectrons

Reducingagent–speciesthatreducesanotherspecies

Itisitselfoxidized–loseselectrons

ReducingandOxidizingAgents:

Oxidationnumber(akaoxidationstate)–actualchargeanatominamoleculewouldhaveifalltheelectronsitwassharingweretransferredcompletely,notshared

FormalChargevs.OxidationNumber

Formalchargesareusedtoexamineresonancehybridstructures

Oxidationnumbersareusedtomonitorredoxreactions

FormalCharge

Bondingelectronsareassignedequallytotheatoms

Eachatomhashalftheelectronsmakingupthebond

FormalCharge=valencee-–(unbondede-+½bondinge-)

OxidationNumber

Bondingelectronsaretransferredcompletelytothemoreelectronegativeatom

Half-Reactions

Redoxreactionscanbewrittenintermsoftwohalf-reactions

Oneinvolvesthelossofelectrons(oxidation)

Theotherinvolvesthegainofelectrons(reduction)

Example:Fe2++Ce4+→Fe3++Ce3+

Abalancedredoxequationhastohavechargebalance

Numberofelectronslostintheoxidationhalf-reactionmustbeequaltothenumberofelectronsgainedinthereductionhalf-reaction

RulesforBalancingRedoxReactionsBalancingRedoxEquationswithIon-ElectronMethodorHalf-ReactionMethod

Writetwohalf-reactionsandbalancebothfor:

Thenumberofthekeyatom(i.e.theatomchangingoxidationnumbers)

Changeinoxidationnumberwithelectrons

Addhalf-reactionssoelectronscancel

BalancechargewithOH-(ifthereactionisoccurringinabase)orH+

(ifthereactionisoccurringinanacid)

BalanceOatomswithH2O

Checkthatthereisnonetchangeinchargeornumberofatoms

OxidationNumberMethod

Determineoxidationnumberofatomstoseewhichonesarechanging

Putincoefficientssothatnonetchangeinoxidationnumberoccurs

Balancetheremainingatomsthatarenotinvolvedinchangeofoxidationnumber

Example:Considerthereaction:HNO3+H2S→NO+S+H2O

Oxidationnumbers:N=5,S=-2→N=2,S=0

Ngoesfrom5→2

Δ=−3reduction

Sgoesfrom-2→0

Δ=+2oxidation

MultiplyNby2andSby3

2HNO3+3H2S→2NO+3S+H2O

BalanceOinH2O

6(Ox)→2(Ox)+4H2O

Writethefinalreactionandmakesureitisbalanced(samenumberofatomsonleftandrightside)

2HNO3+3H2S→2NO+3S+4H2O

Voltaic(Galvanic)Cells

Voltaiccellsareelectrochemicalcellsinwhichaproduct-favored(spontaneous)redoxreactiongeneratesanelectriccurrent.Thereactionproducesanelectronflowthroughanoutsideconductor(wire).Requirementsforvoltaiccells:

Anode-anelectrode(i.e.conductorsuchasmetalstriporgraphite)whereoxidationoccurs

Cathode-anelectrodewherereductionoccurs

Saltbridge-tubeofanelectrolyte(sometimesinagel)thatisconnectedtothetwohalf-cellsofavoltaiccell

Saltbridgeallowstheflowofionsbutpreventsthemixingofthedifferentsolutionsthatwouldallowdirectreactionofthecellreactants

Chargedoesnotbuildupinhalfcells

Electricalneutralitymustbemaintained

CellDiagrams

Celldiagramsareshorthandrepresentationforanelectrochemicalcell.

Anodeisplacedontheleftside

Cathodeisplacedontherightside

Singleverticallinerepresentsaboundarybetweenphases,suchasbetweenanelectrodeandasolution

Adoubleverticallinerepresentsasaltbridgeorporousbarrierseparatingtwohalf-cells

ElectronPotential

Electronflowingalvaniccellcandowork/produceenergy

Electricalpotentialenergyismeasuredinvolts

1volt=(1joule)/(1coulomb)

Coulombs=amperesxseconds:

C=AxsorA=C/s

StandardCellVoltages

Cellvoltagescanbemeasuredunderstandardconditions:1atmpressure,250C,and1.0Mconcentrations

DenotedasE0cell

Thestandardcellpotentialisthesumofthestandardpotentialsfortheoxidativehalf-reactionandthereductivehalf-reaction

IfE0cellispositive,thenetcellreactionissaidtobeproduct-favored

(spontaneous)

IfE0cellisnegative,thenetcellreactionissaidtobereactant-favored

(nonspontaneous)

StandardElectrodePotentials

Standardelectrodepotentialsaremeasuredforhalf-reactions,relativetoastandardhydrogenelectrodepotential(whichhasanassignedvalueof0volts).

Eachhalfreactioniswrittenasareduction

Eachhalfreactioncouldoccurineitherdirection

Themorepositivethestandardelectrodepotential,thegreaterthetendencytoundergoreduction

Thatmeansitisagoodoxidizingagent

Themorenegativethestandardelectrodepotential,thegreaterthetendencytoundergooxidation

Thatmeansitisagoodreducingagent

Ifahalf-reactioniswritteninthereversedirection,youmustflipthesignofthecorrespondingstandardelectrodepotential

Ifahalf-reactionismultipliedbyafactor,thestandardelectrodepotentialisnotmultipliedbythatfactor

CellPotentialandGibbsFreeEnergy

SinceapositiveE0cellindicatesaspontaneousreaction,youmight

imaginethereisrelationshipbetweenE0cellandfreeenergy(ΔG0)

ΔG0=-nFE0cell

n=#ofmolesofelectronstransferred

F=Faradayconstant=9.65x104

Important:ApositiveE0cellwouldresultinanegativeΔG0,

andanegativeE0cellwouldresultinapositiveΔG0

ElectrolyticCells

Electrolyticcellsconsistofanelectrolyte,itscontainer,andtwoelectrodes,inwhichtheelectrochemicalreactionbetweentheelectrodesandtheelectrolyteproducesanelectriccurrent.

Propertiesofelectrolyticcell

Requiresenergy(intheformofanelectriccurrent)

Nophysicalseparationisneededforthetwoelectrodereactions

Usuallynosaltbridgeisrequired

Conductingmediumismoltensaltoraqueoussolution

Forelectrolyticredoxreaction:

E0cellisnegative

ΔG0ispositive

Kcissmall(<1)

CHAPTER18-NUCLEARCHEMISTRY

RadioactivityRadioactivityistheemissionofionizingradiationorparticlescausedbythespontaneousdisintegrationofatomicnuclei.

Typesofradioactivity:alpha,beta,andgammadecay

AlsopositronemissionConventiontobeawareof:

NuclearEquationSumoftheatomicnumbersonbothsidesofthenuclearequationmustbeequalSumofthemassnumbersonbothsidesofanuclearequationmustbeequal

NuclearEquationExample:

AlphaDecay

Alphaparticlesarenucleardecayparticles

Anunstablenucleusemitsasmallpieceofitself

Alphaparticlesconsistoftwoprotonsandtwoneutrons

Alphaparticlesymbol:α

An particleisaheliumnucleus

AlphaParticle:

Alphaparticlesareejectedfromthenucleusatafairlylowspeed(approximatelyone-tenththespeedoflight)

Theyareaminimalhealthrisktopeopleunlessingestedorinhaled

Largemassnucleitendtousealphaemissionbecauseitisaquickwayforalargemassatomtolosealotofnucleons(eitheraprotonorneutron)

AlphaDecayEquationExample:

BetaDecay

Betaradiationsymbol:βor

Betaemissionisanucleardecayprocessthatejectsahighspeedelectronfromanunstablenucleus

Electronisformedwithinthenucleusbythebreakdownofaneutronintoaprotonandelectron

Theelectronisejectedfromthesystem

Theprotonthatwasformedremainsbehindinthenucleus

Becauseoftheadditionoftheproton,theatomicnumberofanelementincreasesduringbetaemission

Betaemissioncanbeasignificanthealthrisk

BetaDecayEquationExample:

GammaDecay

Gammaradiationsymbol:

Gammaemissionoccursprimarilyaftertheemissionofadecayparticle

Gammaisaformofhighenergyelectromagneticradiation

Itisasignificanthealthrisk

Afteraparticleisejectedfromanucleusthesystemmayhavesomeslightexcessofenergy,orexistinameta-stablestate

Thisslightexcessofenergyisreleasedasgamma

Gammaemissiondoesnotresultinchangeoftheisotopeortheelement

Nomassandnochargechange

GammaDecayEquationExample:

Theasteriskisusedtorepresentthattheelementisinahighenergystate

PositronEmissionAnunstablenucleusemitsapositronApositronhasthesamemassasanelectronbutthechargeis+1

PositronEmissionEquationExample:

Half-life

Half-lifeisdefinedasthetimefor½oftheparentnuclidestodecaytodaughternuclides.

Allradioactivedecayisfirstorder

Rate=

t–time

N-#ofatoms

k=rateconstant

ln(No/N)=k

No-#ofatomsatthestartingtime

Half-lifeformula:

Half-lifeisaconstant

Carbon-14Dating

Carbon-14datingcanbeusedtodateobjectsrangingfromafewhundredyearsoldto50,000yearsold

Carbon-14isproducedintheatmospherewhenneutronsfromcosmicradiationreactwithnitrogenatoms

147N+10n→146C+11H

Livingthingstakeincarbondioxideandhavethesame 14Cto12Cratioastheatmosphere

However,whenaplantoranimaldies,itstopstakingincarbonasfoodorair

Radioactivedecayofcarbonstartstochangetheratioof 14C/12C

Bymeasuringhowmuchtheratioislowered,wecandeterminehowmuchtimehaspassedsincetheplantoranimallived

Half-lifeofcabon-14is5,720years

FissionandFusionInfission,alargemassnucleusissplitintotwoormoresmallermassnuclei

FissionEquationExample:

Infusion,smallmassnucleiarecombinedtoformalargermassnucleus

FusionEquationExample:

Fusionrequiresveryhightemperatures(inthemillionsofdegrees)sothatsmallnucleicancollidetogetheratveryhighenergies

CONCLUDINGREMARKS

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