参考教程instructordremailoscarchun讲稿

GeneralGeneralChapter9:MolecularGeometriesandBondingTheoriesInstructor:DrO6S4C4Ar)LungWaCHUNG(钟龙华)(Email:oscarchung@)DepartmentofChemistrySupplementaryClass,SupplementaryClass,QuizII,Mid-termExam&AssignmentsMid-termexam(2Date:21(Sat)Nov(2-4BringyourstudentIDandsimpleChapters1-QuizDate:10-11BringyourstudentID&simpleChapters5-Chapter8(Ch08):Duedate(5thNov.(Thu),9Chapter9(Ch09):willbereleasedinthisReviewonChapterLewisSymbols,ReviewonChapterLewisSymbols,LewisStructure,OctetIonicBond:LatticeCovalentBond:Polar,DipoleMoment,FormalCharge,BondStrength/Enthalpy(BondDissociationEnergy)MetallicElectronegativity,Resonance,localizedanddelocalizedOutlineofChapterOutlineofChapterValence-ShellElectron-PairRepulsionTheory(VSEPR):(Non)Bondingpairs,ElectronDomains,MolecularGeometryValenceBond(VB)Theory:Overlap,HybridOrbital,MolecularOrbital(MO)Theory:BondingMolecularOrbital,Anti-bondingMolecularOrbital,BondOrder,Energy-LevelDiagramEducationIncaramagnetismMolecularTheshapeofMolecularTheshapeofamoleculeplaysanimportantroleinitsreactivityandproperties.•Bycountingthenumberofbonding&bondingelectronpairs,wecaneasilypredicttheshapeofthemolecule.WhatDeterminestheShapeofaElectronWhatDeterminestheShapeofaElectron(bondingbonding),repeleach•Byassumingtheelectronpairsareplacedasfaraspossiblefromeachother,wecanpredicttheshapeoftheValence-ShellPairRepulsionValence-ShellPairRepulsion(价层电子对排斥理©212rsct,entRonaldJamesElectron•Electrondomainsisaregionwhereelectronsstaymostlikely:Electronpairs(bondingornon-bondingpair).•EachElectron•Electrondomainsisaregionwhereelectronsstaymostlikely:Electronpairs(bondingornon-bondingpair).•Eachelectroncontributesone•Thecentralatom,A,fourelectronTheleft&rightB•Foradoubleorbond,allelectronssharedbetweenthosetwoatomsareonlycountedasoneelectrondomainintotal.•havefourelectron•ThetopBatomthreeelectron(,“Thebest(,“Thebestarrangementofagivennumberofelectrondomainsistheonethatminimizestherepulsionsamongthem.”Å:10-10•Allmustdois•AllmustdoistocountthenumberofdomainsintheLewis•Theelectron-domaingeometrycorrespondsthenumberofelectronTheTheelectron-domaingeometriesfortwothroughsixelectrondomainsaroundacentralatom.MolecularTheelectron-domainMolecularTheelectron-domaingeometryisoftennotshapeoftheThemoleculargeometryisdefinedby••arrangementofonlythebondedatomsinthemolecules,notthenon-bondingpairs.WithinWithineachelectrondomain,then,therecouldbemorethanonemoleculargeometry.Using1)Using1)DrawupLewisstructureforthemoleculeorCountthenumberofelectrondomainsforthecentralatom:ForBrF5,n=6.Relatentothetypeofstructure.E.g.n=6,octahedral(electron-domainPlacelonepairsinexpectedpositions,maximizingseparationoflonepairs.FormoleculargeometryofBrF5,ignoreonelonepair➔squarepyramidal.LinearElectron•InLinearElectron•Inthelineardomain,thereisonlyonegeometry:•Ifthereareonlytwoatomsinthemoleculethemoleculeislinearnomatterwhattheelectrondomainis.3ElectronDomains:3ElectronDomains:Trigonal•2possiblemoleculargeometries:Trigonalplanar,ifalltheelectrondomainsarebonding;Bent,ifoneofthedomainsisanon-bonding•DoublebondisDoublebondisstillcountedasonlyoneelectronn=3➔Electron-domainMoleculargeometry:trigonal4ElectronDomains:4ElectronDomains:•3possiblemoleculargeometries:Tetrahedral,ifallarebondingpairs,Trigonalpyramidal,ifoneisanon-bonding212es,I5Electron5ElectronDomains:Trigonal•4possiblemolecular•Thereare2distinctpositionsinthisgeometry:•Thereare2distinctpositionsinthisgeometry:Axial(赤道位Lower-energyconformationsLower-energyconformationsresultfromhavingnon-bondingelectronpairsinequatorial,ratherthanaxial,positionsinthisgeometry.6ElectronDomains:6ElectronDomains:••Allpositionsaresame3possiblemolecularSquareplanar;NonbondingPairsandBondNonbondingPairsandBondNon-bondingpairs(lonepairsLP)arephysicallylarger(morediffuse&occupymorespace)thanbondingpairs(BP)•Repulsionswithnon-bondingaregreaterandbondanglesarecompressedawayfromthelonepairs➔decreasebondanglesinamolecule(moleculargeometry):Repulsions:LP-LP>LP-BP>BP-MultipleBondsandBond•MultipleBondsandBond•Doubleandtriplehavegreaterelectrondensityononesideofthecentralatomthandosinglebonds.•Therefore,theyaffectbondangles(longerC-Clbondscanaffectaswell:NH3,107o;PH3,LargerInlargermolecules,itmakesmoresensetotalkaboutLargerInlargermolecules,itmakesmoresensetotalkaboutthegeometryaboutaparticularatomratherthanthegeometryofthemoleculeasawhole.IfacentralatomissurroundedbyIfacentralatomissurroundedbysixelectrondomains,thetermusedtodescribeitsfundamentalgeometryissquareplanar.squarepyramidal.d.Thegeometryofthephosphorustrichloride(PCl3)moleculeisd.trigonalThegeometryofthemethane(CHThegeometryofthemethane(CH4)moleculetrigonalplanar.d.Thegeometryofthexenontetrafluoride(XeF4)moleculeissee-sawd.trigonalFormicacid(HCO2H)hasFormicacid(HCO2H)hasanO-C-Obondangle(X)degreesandaC-O-Hbondangleof(Y)X=~180,Y=b.X=~120,Y=X=~180,Y=d.X=~109.5,Y=AmoleculewhichpossessespolarAmoleculewhichpossessespolarbondsdoesNOTalwaysmeanthatthemoleculeasawholeispolar!ByaddingtheindividualbonddipolesByaddingtheindividualbonddipoles(likesumofvectors),onecandeterminetheoveralldipolemomentforthePolarValenceValenceBondValenceBond(VB)ValenceBond(VB)VSEPRCanpredictmoleculargeometriesCANNOTexplainwhy/howbondsformbetweenValenceBondBondingelectronpairsareconcentratedbetweenOrbitaloverlap➔buildupofe-densitybetweencovalentbondLewis’selectron-pairbonds(bondformationbysharinge-)+atomicorbitals(usingquantummechanics)and•Covalentand•Covalentbondsthroughthesharingby•Insuchanthiscanonlyoccurwhenhalf-filledorbitalsonthetwoatomsoverlap(regiontheelectronsareinH2•ShortentheinH2•Shortenthebonddistance(electronsandbecomecloser),increasesoverlapofthetwoatomicorbitals(moresharingelectrons)andenergydecreases.•Iftheatomsgettooclose,theinternuclear(nuclei–nucleirepulsion)greatlyraisestheHybridConsiderHybridConsiderInitselectronicgroundstate,berylliumwouldnotbeabletoformbonds,becauseithasnosinglyoccupiedorbitals.Ifitabsorbsthesmallamountofenergyneededtopromoteanelectronfromthe2stothe2porbital,itcanformtwobonds.However,itstillcannotexplainthegeometrybyusing2sand2pMixingonesorbitalandMixingonesorbitalandoneporbitalyieldstwodegenerateorbitals:hybridsofthetwoorbitals.–ThesesphybridorbitalshavetwolobeslikeaOneofthelobesasisthesislargerandmore–Eachsphybridorbitalcontains50%sorbitaland50%porbitalcharacters(ones+oneptwosphybridorbital)–2p•Withhybridorbitals,2p•Withhybridorbitals,theorbitaldiagramforwouldlooklike•Thesporbitalsarehigherinenergythanthe22rnc,werthanthe•Thesetwodegenerateorbitals•Thesetwodegenerateorbitalswouldthemselves180fromeach•Thisisconsistentwiththeobservedgeometryberylliumcompounds:UsingasimilarmodelforboronleadstothreedegenerateUsingasimilarmodelforboronleadstothreedegeneratesp2orbitals(ones+twopthreesp2hybridorbital:33%s&67%porbitalcharacters).•Withcarbon,wefour•Withcarbon,wefourdegenerateorbitals(ones+three25%s&75porbital•Energyorderofs,sp,sp2&Water••Water••Whyisit104.5°insteadofOxygenhas4electron→sp3HybridOrbitalHybridOrbitalDrawtheLewisstructureforthemoleculeordeterminetheelectron-domaingeometrybyVSEPRSpecifythehybridorbitalsneededtoaccommodatetheelectronpairsbasedontheirgeometricarrangement.ValenceBond(VB)HybridizationisValenceBond(VB)Hybridizationisamajorplayerinthisapproachtobonding.•TherearetwobasicwaysorbitalscantoformbondsbetweenLinusCarlFritzWolfgangGilbertNewtonSigma()Sigma()ssddSigmabondsarecharacterizedbyhead-to-headoverlapexceptforsorbitals.Cylindricalsymmetryofincreasedelectrondensityabouttheinternuclearaxis.Pi()ddPiPi()ddPibondsarecharacterizedbyside-to-sideoverlapwith1nodalplane.Increasedelectrondensityaboveandbelowtheinternuclearaxis.Less(effective)overlap:weakerthansigmabond.(lesseffectiveforthethird-roworbelow•••©212ron.ExtraInfo.Delta()ExtraInfo.Delta()ddDeltabondsarecharacterizedbyside-to-sideoverlap(e.g.with2dorbitals)with2nodalEvenless(effective)overlap:weakerthan••SingleBondsSingleBonds&MultipleSinglebondsarealwaysbonds,becauseoverlapisgreater,resultinginastrongerbondandmoreenergylowering(morestable).Inamultiplebond,oneofthebondsisabondandtherestare(andsometimesbondsfortransitionmetals)bonds.•In•Inamoleculelikeformaldehyde,ansp2orbitalcarbonoverlapsinfashionwiththecorrespondingorbitalontheoxygen.TheunhybridizedporbitalsoverlapinIntriplebonds,asinacetylene,twosporbitalsIntriplebonds,asinacetylene,twosporbitalsformabondbetweenthecarbons,andtwopairsofporbitalsoverlapinfashiontoformthetwobonds.DelocalizedElectrons:DelocalizedElectrons:WhenwritingLewisstructuresforspecieslikethenitrateion,wedrawresonancestructures(moreLewisstructures)tomoreaccuratelyreflectthestructureofthemoleculeorion.•Inreality,eachoffour•Inreality,eachoffouratomsinthenitrateionhasaporbital.•Theporbitalsonthreeoxygensoverlapwiththeporbitalonthecentralnitrogen.Thismeanstheelectronsarenotlocalizedbetweenthenitrogenandoneoftheoxygens,butratherarethroughouttheion.TheTheorganicmoleculebenzenehassixC-Cbondsandaporbitaloneachcarbonatom.InrealitytheelectronsInrealitytheelectronsinbenzenearenotlocalized,butdelocalized(C-C(benzene):1.40Å;typicalC-C:1.54Å;typicalC=C:1.34Å)TheevendistributionoftheelectronsinmakesthemoleculeunusuallyTherearenocommonEachoccursaboutthecentralatomonly.EachrepresentsTherearenocommonEachoccursaboutthecentralatomonly.Eachrepresentsasingleelectrondomain.AllexistwhenaparticularLewisstructureisWhichmoleculeisd.WhichmoleculeisWhichmoleculeisd.Thehybridizationoftheoxygenatominawatermoleculeisd.ThecentralatomofwhichmoleculebelowThecentralatomofwhichmoleculebelowisd.Amoleculeofacetonitrile(CH3CN) sigma234d.AmoleculeofcrotonaldehydeAmoleculeofcrotonaldehyde(CH3CH=CH-CH=O)contains pibonds.123d.For3For3electron-e.g.For4electron-e.g.Numberof-bonds+lone-pairs(==electrondomains)=numberofhybridorbitalsrequired;Then,unhybridized2porbitalscouldbeusedfor-bonds.Molecular-OrbitalMolecular-OrbitalMolecular-Orbital(MO)ValenceBondMolecular-Orbital(MO)ValenceBondtheory(+Canpredictmoleculargeometries&explainwhy/howbondsformbetweenatomsCANNOTpredictmagnetic&excitedstatesMolecular-Wavenatureofelectrons(quantumLinearcombination(线性组合ofwavefunctions(oratomicorbitals)ofallatomselectronsarefoundinorbitalsofthewholeRobertSandersonFriedrichHermannWaveNatureWaveNatureofDifferentphasesTwowaysforoverlappingoftwoatomicorbitals:(1)1sorbitalsoverlappinghavethesamesign(phase相)ofthewavefunction(netoverlap);(2)thetwoorbitalsareofoppositesign(Twowaysforoverlappingoftwoatomicorbitals:(1)1sorbitalsoverlappinghavethesamesign(phase相)ofthewavefunction(netoverlap);(2)thetwoorbitalsareofoppositesign(nonetoverlap).-++©SamesignofLowerbondingOppositesignofHigherenergyanti-bondingorbitalAmplitudesofwavefunctionsaddedAmplitudesofwaveAmplitudesofwavefunctionsaddedAmplitudesofwave1-+(干涉MOtheoryconsiderthewavenatureMOtheoryconsiderthewavenatureoflinearcombinationofwavefunctions(c2:(1s)=c11-bondingmolecular(1s)=c11+c22ForH2:c1=c2Energy-level(MO)•InH2theelectronsgoEnergy-level(MO)•InH2theelectronsgointothebondingmolecularorbital:1s2•Thebondorderonehalfthedifferencebetweenthenumberofbondingandantibondingelectrons.E211(2−0)=2bondorder=½(bondingelectrons-antibonding•Inthe•InthecaseofHe2(1s21s2),thebondorderwould2(2−2)=Therefore,He2doesnotexist.Bondorder=Bondorder=(2-=Bondorderfor2MO(LUMO)MO(HOMO)BondorderMO(LUMO)MO(HOMO)Bondorder=(2-(1s2=EffectsofpForEffectsofpForatomswithbothsandporbitals,thereare2typesofThesandtheporbitalsthatfaceeachotheroverlapinTheothertwosetsofporbitalsoverlapinfashion(sideway).•Both&Both&bondingMOs&*and*antibondingMOs.•Thestrongerbond,lowerenergytheMO&highersnat,•Orbitalenergydifference•Orbitalenergydifference2sand2pincreaseslefttorightofthesecondperiodofperiodic•Atomicorbitalsinteractmosteffectivelywithatomicorbitalsofsimilar2sand2pz2sand2pzorbitalscanfurtherinteract/mix(ina•fashion):thesmallerp-blockelementsintheperiodhaveasizableinteractionbetweenthes&σ2s:decreaseMOenergy;σ2p:increaseMOflipstheorderoftheandMOsinB,C&EnergyLevelsofSecond-RowHomonuclearDiatomicMoleculesN:EnergyLevelsofSecond-RowHomonuclearDiatomicMoleculesN:half-π(2p)higherinenergythanσ(2p)π(2p)lower22rc,BOBO=(2-=BOBO=(4-=BO=(6-BO=(6-=NNSecond-RowMOSecond-RowMO•AO+AO•AO+AObondingMO+•Moveσ2pinenergythanπ2ponlyforB2,C2&N2(half-filledp•Putelectronsatomiccases:orbitalfirst,max.1pairelectronswithdifferentspinoneachMOLiquidLiquidLiquidLiquidTypesofTypesofDiamagnetism反磁性referstomaterialsthatarenotaffectedbyamagneticfield.Paramagnetism(顺磁性):referstomaterialslikealuminumorplatinumwhichbecomemagnetizedinamagneticfieldbuttheirmagnetismdisappearswhenthefieldisremoved.Ferromagnetism铁磁性referstomaterialssuchasironandnickel)thatcanretaintheirmagneticpropertieswhenthemagneticfieldisEnergy-leveldiagramforNO(HeteronuclearDiatomicMolecules)•TheEnergy-leveldiagramforNO(HeteronuclearDiatomicMolecules)•Theelectronegativity,thelowerenergyoftheatomicorbital(AO)•AnMOhasacontributionfromtheAOwithacloserinExtraInfo.ExtraInfo.Accordingtomolecularorbitaltheory,theAccordingtomolecularorbitaltheory,thebondorderinthedinitrogen(N2)moleculeisd.No,becausethebondorderisYes,becausethebondorderisYes,becausethebondorderisD.Yes,becausethebondorderisRemainbonded,asthebondordertheRemainbonded,asthebondordertheFallapart,asthebondorderchanges1toRemainbonded,asthebondorderfrom1toFallapart,asthebondorderchanges1toWhatdifferenceinWhatdifferenceinelectronconfigurationaccountsformostofthedifferencebetweenthebondenthalpyofN2andthatofF2?A.F2containsmoreelectronsthanN2andthesegointotheantibondingπ*2porbitalandthebondorderB.Thechangeintheorderofπ2pandσ2pMOsfromN2toF2reducesthe