复旦大学无机化学考研5课件

4.PeriodicanomaliesofthenonmetalsandposttransitionmetalsReluctanceoffourth-rownonmetalstoexhibitmaximumvalenceThereisadefinitetendencyforthenonmetalsoftheforth-row,As,Se,Br,tobeunstableintheirmaximumoxidationstate.Forexample,AsCl5aswellasAsBr5andAsI5isunknownalthoughbothPCl5andSbCl5exist.TheonlystablearsenicpentahalideisAsF5.

Inoxygengroupthesamephenomenonisencountered.

TheenthalpiesofformationofSF6,SeF6,andTeF6are–1210,-1030,and–1315kJmol-1,respectively.ThisindicatesthatcomparablebondenergiesforS-FandTe-FbondsaremorestablethanSe-Fbond.Thereluctanceofbrominetoaccepta+7oxidationstateiswell-known.Perbromicacid(HBrO4)andperbromateion(BrO4-)hadnotbeensynthesizedbefore1968.Theyareunstable.Thustheperbromateionisastrongeroxidizingagentthaneitherperchlorate(ClO4-)orperiodate(IO4-).(83SeO42-→BrO4-+e-)Indicatingthestabilityof4s2tosomeextent.(2)Theinert-s-paireffectAmongtheheavyposttransitionmetalsthereisadefinitereluctancetoexhibitthehighestpossibleoxidationstateorthegreatestcovalence,whichmeansthattheheavyelementsinCarbongroupusuallyshow+2oxidationstate(divalent,asGe2+,Sn2+,Pb2+)andBoronGroup+1oxidationstate(monovalent).Itispossibletopreparedivalentgermanium,tin,andleadcompounds.IncarbongroupTinhasastable+2oxidationstateinadditionto+4andforleadthe+2oxidationstateisfarmoreimportant.OtherexamplesarestableTl+andBi3+.Thesestableoxidationstates,twolessthanthehighestoxidationstatesoftheelements,haveledtothesuggestionthatthepairofselectronsisinertandonlythepelectronsareemployedinthebonding.Ithasalsobeensuggestedthattheunreactivityofmetallicmercury(Hg)isduetotheinert6s–pairelectrons,becausetheonlybondingelectronsofmercuryare6selectrons,whichresultsintheweakmetalbondandfurthermoretheliquidstateofHg.(3)AnomaliesofGroupsBoronandCarbonCarbongroupinvolvesatendencyforGetoresembleCmorethanSi.Someexamplesare:(i)Reductionofhalideswithzincandhydrochloricacid.GeresemblesCandSnresemblesSi.ZnR3C-X→R3C-HHClZnR3Si-X→NoR3Si-HHClZnR3Ge-X→R3Ge-HHClZnR3Sn-X→NoR3Sn-HHCl(ii)Reactionoforganolithiumcompoundswith(C6H5)3YH(Y=ElementofCarbonGroup).Triphenylmethaneandtriphenylgermanedifferintheirreactionwithorganolithiumcompoundsfromtriphenylsilaneandtriphenylstannane:φ3CH+LiR→LiCφ3+RHφ3SiH+LiR→φ3SiR+LiHφ3GeH+LiR→LiGeφ3+RHφ3SnH+LiR→φ3SnR+LiH(iii)BoronGroupTheelementsofBoronGroupshowsimilarpropertiesalthoughthedifferencesarenotsonoticeableasforCarbonGroup.Itmaybenotedthatthecovalentradiusgallium(Ga)appearstobeclosetothatofaluminum(Al):rGa=120pm,rAl=130pmThefirstionizationenergiesofthesetwoelementsaresurprisinglyclose:I1(Al)=578kJmol-1,I1(Ga)=579kJmol-1(Gaisjustafterthefull3d10,calledScandiumContractionsimilartoLanthanideContraction)InBoronGroup,thesumofthefirstthreeionizationenergiesshowsasimilartendencyasCarbonGroup:IonizationEnergy(kJmol-1) I1+I2+I3 I1+I2+I3+I4

B=6887 C=14282Al=5044 Si=9950Ga=5521Ge=10011In=5084 Sn=8994Tl=5439 Pb=8617(4s2and6s2pairsaremoreinert)(4)Loose-compactModelRelativisticEffectsAccordingtoEinstein’stheoryofrelativity,themassmofaparticleincreasesfromitsrestmassm0whenitsvelocityvapproachesthespeedoflight,c,andmisthengivenbytheequation:

m=m0/[1-(v/c)2]1/2Forahydrogenatom,theBohrmodeloftheatomleadstothevelocityoftheelectronbeingexpressedbytheequation:

v=Ze2/(2ε0h)=2.167×106m/s=1au(atomicunit)Comparewiththespeedoflight:c=2.998×108m/s=137auThemassof1selectronofHatomisclosetom0(m/m0=1.00003).However,foranatomwithatomicnumberZ,thevelocityof1selectronofthisatomreachesapproximatelyZau.e.g.Z=80,Hg,v/c=0.58,leadingtom=1.2m0

SincetheradiusoftheBohrorbitisgivenbytheequation:

r=(n2h2ε0)/(πmZe2)theincreaseinmresultsinanapproximately20%contractionoftheradiusofthe1s(n=1)orbital;thisiscalleddirectrelativisticcontraction.Othersorbitalsareaffectedinasimilarwayandasaconsequence,whenZishigh,sorbitalshavediminishedoverlapwithorbitalsofotheratoms.Adetailedtreatmentshowsthatporbitalsalsoundergoadirectrelativisticcontraction.Ontheotherhand,dorbitalsundergoanindirect

relativisticexpansion;asimilarargumentappliestoforbitals.Withincreasingnucleinumber1s2pairwillbegraduallyattractedtothenuclei.TheshieldingparameterontotheelectronsofthesecondshellwillbehigherthanthatexpectedbySlater’sRules.Thus,theseelectronsarein“loose”state.Thentheeffectivenuclearchargeontotheelectronsofthethirdshellincreasesandtheseelectronsarein“compact”state.Thiseffectextendsoutershellsonebyonealternatively.Loose-compacteffect

ForIA,IIAelementsPeriod234567Compact1s21s21s21s21s21s2Loose2s1-22s22p62s22p62s22p62s22p62s22p6Compact3s1-23s23p63s23p63s23p63s23p6LooseΔsmall4s1-24s24p64s24p64s24p6CompactΔbig5s1-25s25p65s25p6LooseΔsmall6s1-26s26P6CompactΔbig7s1-2ΔsmallCsandBaarethemostelectropositiveinIAandIIA,respectively.CsexhibitsthehighestatomicradiumamongtheknownatomsofPeriodicTable.MLiNaKRbCsI1/kJmol-1520496419403376Δ24

77

16

62χ0.980.930.820.820.79Δ

0.05

0.11

0.00

0.03r/pm156186231243265Δ30

45

12

22FortheotherelementsPeriod23456Compact1s21s21s21s21s2Loose2s22p1-62s22p62s22p62s22p62s22p6Compact3s23p1-63s23p63s23p63d103s23p63d10Loose3d104s24p64s24p64d104f14Compact4s24p1-64d105s25p6Loose5s25p1-65d10Compact6s26p1-6Therearetwoadditionaleffectsshouldbeconsidered,fortheneighboringshells:s2andd10

haveverysmallshieldingparameters.Therefore,weshouldconsiderthesumofthesethreeeffects.Forthes-andd-block(innerp6),nochanges.Fortheotherelements:PeriodShellL-Ceffects2ord10effectSum2 2s22p1-6Lweak C C3 3s23p1-6C L L*4 4s24p1-6C C C55s25p1-6L C L6 6s26p1-6Cstrong C C

4s2,6s2,inerts-paireffect*isrelativelyweakerthanthatofPeriod2and4ΔofI1orEA1show“big,small,big,small”trendfromPeriod2to6.Electronicconfigurationofd-block3dVd3s2Crd5s1Mnd5s2Fed6s2Cod7s2Nid8s24dNbd4s1Mod5s1Tcd5s2Rud7s1Rhd8s1Pdd10s05dTad3s2Wd4s2Red5s2Osd6s2Ird7s2Ptd9s14d-blockmetalshavemoreexceptioncomparedwith3dor5d-blockmetals.3dL,4sC;4dC,5sL;5dL,6sC (<d10)Theenergylevelgapbetween4dand5sisbigerwhichfavorsloweringthesumenrergy.ElementCuAgAuPeriod456Configuration3d104s14d105s15d106s1(n-1)d10LCLns1CLCOxidationstate+I,+II+I+I,+IIIAtomicRadium/pm127.8144.4144.2I1/kJmol-1745.5731890I2/kJmol-11957.920741980ThehighestorlowestvaluesofAginthegroupisascribedto“4d10compact,5sloose”→e.g.I1small,I2large1.4ConsiderationBasedonThermodynamicsandKineticsAgoodworkingknowledgeofthermodynamicsisinvaluabletoachemist.Theyareparticularlyinterestedinquantitativeexpressionsforthedrivingforceofchemicalreactions.Thedrivingforcecanbemeasuredintermsofthefreeenergychange(ΔG),theequilibriumconstant(K),thepotentialofthereaction(E),oracombinationofthechangesinheatcontent(ΔH)andentropy(ΔS).Therelationbetweenthesethermodynamicfunctions,anddefinitionsofsomeoftheterms,follow.ΔG=-nEF=-RTIn(K/Q)=ΔH-TΔSHerenisthenumberoffaradaysofelectricityinvolvedinthereaction,andQisthereactionquotient,ortheproductoftheactivitiesoftheresultingsubstancesdividedbytheproductoftheactivitiesofthereactingsubstances,eachactivityraisedtoapowerequaltothecoefficientofthesubstanceinthechemicalequation.aA+bB→cC+dDQ={(fC[C])c(fD[D])d}/{(fA[A])a(fB[B])b}where,a,b,c,anddarecoefficients.Theactivitiesofpuresolidandliquidsubstancesaretakentobeunity.Asafairapproximation,theactivityofagaseoussubstanceisthepartialpressureofthatsubstance,expressedinatmospheres.Forasubstanceinadiluteaqueoussolution,theactivityisroughlyequaltotheconcentration,expressedeitherasmolality(molesperkilogramofwater)ormolarity(molesperliterofsolution).Forconcentratedsolutions,theseapproximationscannotbeused;activitycoefficientdataarerequired.ItwillbenotedthattheequilibriumconstantKisthevalueofQatequilibrium.WhenQ=1(whichisthecasewhenallthereactantsandproductsareatunitactivity),thethermodynamicfunctionspossesstheir"standard"values:ΔG0=-nE0F=-RTInK=ΔH0-TΔS0Weusethermodynamicaldatatoconsidersyntheticproblem.

e.g.Letussupposethatwewishtoprepareperiodate(H3IO62-)byoxidizingiodate(IO3-)withsomeaqueousoxidizingagent.Wecanseethattheperiodate-iodatecouplehasapotentialof1.6Vinacidsolutionsandapotentialof0.7Vinbasicsolutions.H5IO6+H++2e=IO3-+3H2OE0=1.60VH3IO62-+2e=IO3-+3OH-E0=0.70V

Anyoxidizingagentwithareductionpotentialmorepositivethan1.6Vinacidsolutionsormorepositivethan0.7Vinbasicsolutionsisthermodynamicallycapableofoxidizingiodatetoperiodate.Inpractice,hypobromite(BrO-)orhypochlorite(ClO-)isusuallyused,becausetheseoxidizingagentsreactwithreasonablerapidityandarerelativelycheap.Eithermaybeconvenientlypreparedbydissolvingtheappropriatehalogeninanalkalinesolution:Ifweusehypochlorite(ClO-)asoxidizingagent,thereactionis:ClO-+IO3-+OH-+H2O=H3IO62-+Cl-E=0.19VTherefore,periodate(H3IO62-)canbepreparedbyoxidizingiodate(IO3-)withhypochlorite(ClO-)inanalkalinesolution.Whenweworkwiththermodynamicdata,itisalwaysimportanttokeepinmindthatthermodynamicscantelluswhetherareactioniscapableoftakingplace,butitcannottellusthereactionrate.Thus,areactionmaybethermodynamicallyfavored(ΔG<O)andyetproceedextremelyslowly.Therefore,bothkineticsandthermodynamicsmustbeconsidered.AmmoniaSynthesis

TheHaberprocessfortheindustrialsynthesisofammoniaisawell-knownapplicationofbothequilibriumandkineticconsiderationsinsynthesis.Hydrogenandnitrogenreactathightemperaturesandpressuresandinthepresenceofanironcatalystaccordingtothereversiblereaction:N2(g)+3H2(g)=2NH3(g)

TheeffectoftemperatureandpressureontheequilibriumisgivenintheTable.Theformationofammoniaisobviouslyfavoredbybothlowtemperaturesandhighpressures,butifthetemperaturefallsmuchbelow400℃,therateofthecatalyzedreactionistooslowforeconomicalproduction.Ontheotherhand,ifthetemperatureistoohigh,theequilibriumpressureofammoniaistoolowforsatisfactoryyields.Inpractice,pressuresaround1000atmandtemperaturesaround500℃areemployed.DiamondSynthesis

Diamondisthermodynamicallyunstablewithrespecttographiteat1atmpressureatalltemperatures.Fortheprocess,Cgraphite→Cdiamond

ΔG0=692calmole-1at25℃andΔG0=2400calmole-1at1200℃Inasmuchasthemolarvolumesofdiamondandgraphiteare3.42and5.34cm3,respectively,hencethedensitiesofdiamondandgraphiteare3.541and2.266gcm-3.Therefore,thedrivingforcefortheconversionisincreasedbyincreasingthepressure.

AplotofthepressurerequiredtomakeΔG=0againsttemperatureisgivenintheFigure.

Forthereactiontoproceedatanappreciablerate,itisnecessarytogototemperaturesaboveapproximately1800K.Therefore,asshownintheFigure,pressuregreaterthanabout60,000atmisrequiredinthesynthesis.Anotherimportantfeatureistheuseofasolventtopermittakingapartthegraphitelatticeatom-by-atomandbuildingtheatomsintothediamondlattice.Inthefirstsynthesisofadiamond,FeSwasthesolvent;thetemperaturewasabout1920K;thepressurewasabout90,000atm,andthereactiontimewas3min.

Inrecentyears,anumberofinvestigatorshavesucceededingrowingdiamondsatlowpressuresbypyrolyzingthevaporsoforganiccompounds,usingChemicalVaporDeposition(CVD)method.Oneprocessinvolvespassingmethane,atapressurearound0.2mmHg(mercury),overadiamondseedcrystalatabout1050℃.Afterdepositionofcarbonontheseedcrystal,anygraphitethathasformediseliminatedbyreactionwithhydrogenat1033℃and50atm.Therefore,theequilibriumismovedtowardthedirectionofdiamondformation.(NonequilibriumThermodynamics)1.5AcidsandBasesChemicalreactionsincludethreetypesofreactions:RedoxreactionCoordinationreactionDoubledecompositionreaction(containingAcid-basereaction)Onthestandofchemicalbond,achemicalreactioninvolvestheformationand/orcrackofoneormorebonds;Onthestandofenergy,achemicalreactionisaccompaniedwithabsorptionorreleaseofenergy;Onthestandofchargedistribution,chargedensitiesofreactantsandproductswillre-distributealongtheenergy-favoredpath.

Duringredoxreaction,chargestransferamongtheatomsandtheoxidationstatesoftheatomschange;Duringcoordinationreaction,chargestransferamongthecentralatom/ionandligands;Duringdoubledecompositionreaction,chargesredistributeortransferamongthereactantsbuttheoxidationstatesremainunchanged.

Accordingtosomedefinitionsbelow,thesethreetypesofreactionscanbesimplybelongtoacid-basereaction.1.5.1Definitionsofacidsandbases

Therearemanydifferentdefinitionsofacidsandbases.Thefirstrecognitionoftheexistenceoftheclassesofcompoundwenowidentifyasacidsandbaseswerebasedontasteandfeel:acidsweresourandbasesfeltsoapy.Hereweintroducesomemoderndefinitions.1.Brönsted-LowrydefinitionIn1923,J.N.BrönstedandT.M.Lowryindependentlysuggestedthatacidsbedefinedasprotondonorsandbasesasprotonacceptors.

AcidBaseH3O+

+OH-

2H2ONH4+

+NH2-

2NH3H3SO4+

+HSO4-

2H2SO4NH4+

+S2-

NH3+HS-Thisdefinitionalsointroducedtheconceptofconjugateacidsandbasesanddescribedthereactionsasoccurringbetweenastrongeracidandbasetoformaweakeracidandbase:H3O++NO2-

→H2O+HNO2acid1base2base1acid2Conjugateacid-basepairs:AcidBase

H3O+H2O

HNO2NO2-

H2OistheconjugatebaseofH3O+andHNO2istheconjugateacidof

NO2-.Thedirectionofthereactionalwaysfavorstheformationofweakeracidsorbasesthanthereactants.H3O+isastrongeracidthanHNO2andNO2-isastrongerbasethanH2O.2.Lux-FlooddefinitionIncontrasttotheBrönsted-Lowrydefinitionthatemphasizestheprotonastheprincipalspeciesinacid-basereactions,thedefinitionproposedbyLuxandextendedbyFlooddescribesacid-basebehaviorintermsoftheoxideion(O2-).Acidsaredefinedasoxideionacceptorsandbaseasoxideiondonors.Thisconceptcanbeadvancedtotreatnonprotonicsystems,suchasthesystemofmoltenoxide.

AcidBase

SiO2

+CaO

CaSiO3

H2O+CaO

Ca(OH)2

TiO2

+BaCO3

BaTiO3+CO2O2-

3.IonotropicdefinitionAccordingtothisdefinition,theacidisdefinedasacharacteristiccationdonorandthebaseasacharacteristiccationacceptor.Brönsted-Lowrydefinitionisoneexamplethatdefinesproton(H+)asthecharacteristiccation.Andalso,theacidcanbedefinedasacharacteristicanionacceptorandthebaseasacharacteristicaniondonor.Lux-Flooddefinitionisoneexamplethatdefinesoxideion(O2-)asthecharacteristicanion.4.Solventsystemdefinition

Manysolventsautoionizewiththeformationofacationicandananionicspeciesasdoeswater:2H2O↔

H3O++OH-2NH3

↔NH4++NH2-2H2SO4↔H3SO4++HSO4-2OPCl3

↔

OPCl2++OPCl4-2BrF3

↔BrF2++BrF4-Forthetreatmentofacid-basereactions,itisconvenienttodefineanacidasaspeciesthatincreasestheconcentrationofthecharacteristiccationofthesolventandabaseasaspeciesthatincreasestheconcentrationofthecharacteristicanion.

e.g.Inwater:HCl(g)+H2O(l)H3O+(aq)+Cl-(aq)

AcidBaseHClincreasestheconcentrationofthecharacteristiccation,[H3O+],inwater,thusHClisanacid.NaOH(g)+xH2O(l)Na(H2O)x+(aq)+OH-(aq)

BaseAcidNaOHisabase.InPOCl3FeCl3(s)+POCl3(l)→POCl2+(sol)+FeCl4-(sol)AcidBaseSOCl2(l)+POCl3(l)

→POCl4-(sol)+SOCl+(sol)BaseAcid(亚硫酰氯)InBrF3SbF5

+BrF3

→BrF2++SbF6-AcidBaseKFinBrF3F-+BrF3→BrF4-

BaseAcidClassifictionofsolvents

ProticSolventsSolventAcidCationBaseAnionpKion(25oC)B.P.(oC)H2SO4H3SO4+HSO4-3.4(10oC)33.0HFH2F+HF2-~12(0oC)19.5H2OH3O+OH-14100CH3COOHCH3COOH2+CH3COO-14.45118.2CH3OHCH3OH2+CH3O-18.964.7NH3NH4+NH2-27-33.4CH3CNCH3CNH+CH2CN-28.681ThepKionistheautodissociationconstantforthepuresolvent,indicatingthat,amongtheseacids,H2SO4dissociatesmuchmorereadilythananyoftheothers,andthatCH3CNisleastlikelytoautodissociate.Theboilingpointsaregiventoprovideanestimateoftheconditionsunderwhicheachsolventmightbeused.AproticSolventsNonpolar:C6H6,CO2,CCl4,etc.Polar:BrF3,IF5,N2O4,SO2,C5H5N,(CH3)2SO,OPCl3,CH3(OCH2CH2)2OCH3,COCl2,

SOCl2,etc.N2O4↔NO++NO3-2SO2↔SO2++SO32-

SOCl2↔SOCl++Cl-

5.LewisdefinitionIn1923,G.N.Lewisproposedadefinitionofacid-basebehaviorintermsofelectron-pairdonationandacceptance.TheLewisdefinitionisperhapsthemostwidelyusedofallbecauseofitssimplicityandwideapplicability,especiallyinthefieldoforganicreactions.Lewisdefinedabaseasanelectron-pairdonorandanacidasanelectron-pairacceptor.Inadditiontoallofthereactionsdiscussedabove,theLewisdefinitionincludesreactionsinwhichnoionsareformedandnohydroniumionsorotherionsaretransferred:BaseAcid

R3N+BF3

→R3N-BF

4CO+Ni→Ni(CO)4

2L+SnCl4→SnCl4L2

2NH3+Ag+

→Ag(NH3)2+CpGaI+Cp2CaII→CpGa-CaCp26.UsanovichdefinitionThecompletedefinitionisasfollows:Anacidisanychemicalspecieswhichreactswithbase,givesupcations,oracceptsanionsorelectrons,orcombineswithanionsand,conversely,abaseisanychemicalspecieswhichreactswithacids,giveupanionsorelectrons,orcombineswithcations.ThisdefinitionsimplyincludesallLewisacid-basereactionsplusredoxreactionswhichmayconsistofcompletetransferofoneormoreelectrons.OH-+O=C=O→HOCO2-

e-(sol)+Na(sol)→Na-(sol)

BaseAcidThesedefinitionscanbesummarizedasageneraldefinition,whichdefinesanacidasdonatingapositivespeciesoracceptinganegativespeciesandabaseasdonatinganegativespeciesoracceptingapositivespecies.

AcidBaseDonorH+,M+O2-,eore2,OH-,X-AcceptorO2-,eore2,OH-,X-H+,M+1.5.2Solventleveling

Becausesolventsmaybeacidsorbases,forexample,weakacidsinwatermayappearstronginabasicsolventandsimilarly,weakbasesinwatermayappearstronginanacidicsolvent.1.Discriminationinwater

AnyacidstrongerthanH3O+inwatergivesaprotontoH2O(water)andformsH3O+.ThismeansthatnoacidisstrongerthanH3O+inwater.Forexample,inwaterwecannotknowwhichisthestrongeracidbetweenHBrandHI.Therefore,waterissaidtohavealevelingeffectthatbringsallstrongeracidsdowntotheacidityofH3O+.However,inanacidicsolventsuchasaceticacid(CH3COOH),bothoftheacidsbehaveasweakacidsandtheirstrengthcanbedistinguished.ItisfoundHIisstrongerthanHBr.Similarly,theOH-isthestrongestbaseinwaterthatanybasestrongerthantheOH-reactswithwat