《基础化学》英文教学课件：chapter-10

Chapter10.CovalentBondingandIntermolecularForces§10-1.ValenceBondTheory§10-2.HybridOrbitals§10-3.ValenceShellElectron PairRepulsionTheory§10-4.IntermolecularForcesChapter10.CovalentBondingaChemicalBondsChemicalbond(化学键):Astrongattractiveforcethatexistsbetweencertainatomsinasubstance.Ionicbonds(离子键):

Achemicalbondformedbytheelectrostatic(静电)attractionbetweenpositiveandnegativeions.Ionicbonds,covalentbonds,andmetallicbonds.ChemicalBondsChemicalbond(化《基础化学》英文教学课件：chapter_10《基础化学》英文教学课件：chapter_10ChemicalBondsCovalentbonds(共价键):

Inacovalentbond,twoatomssharevalenceelectrons,whichareattractedtothepositivelychargedcoresofbothatoms.H:H-+diamondChemicalBondsCovalentbonds(《基础化学》英文教学课件：chapter_10ChemicalBondsMetallicbonds(金属键):

ThevalenceelectronsofacrystalofNamovethroughoutthecrystal(delocalizedelectrons),attractedtothepositivecoresofallNa+ions.sodiumSodiumionsValenceelectronsmovethroughoutmetalChemicalBondsMetallicbonds(《基础化学》英文教学课件：chapter_10TheoryofChemicalBonding1.In1916GilbertN.Lewisproposedthatthestrongattractiveforcebetweentwoatomsinamoleculeresultsfromcovalentbond,achemicalbondformedbythesharingofapairofelectronsbetweenatoms.2.In1926WalterHeitlerandFritzLondonshowedthatthecovalentbondinH2couldbequantitativelyexplainedbythenewlydiscoveredtheoryofquantummechanics.F.London（1900-1954）GermanyW.Heilter（left）（1904-1981）SwitzerlandTheoryofChemicalBonding1.ITheoryofChemicalBonding3.TheexplanationofthecovalentbondinH2bythetheoryofquantummechanicscanbeextendedtoothermolecules,resultinginvalencebondtheory(价键理论).4.Basedonvalencebondtheoryandwavepropertiesofelectrons,L.PaulingandJ.C.Slaterproposedhybridorbitaltheory(杂化轨道理论)

in1931.L.Pauling(1901-1994)J.C.Slater(1900-1976)TheoryofChemicalBonding3.TTheoryofChemicalBonding5.In1932R.S.MullikenandF.Hundproposedmolecularorbitaltheory(分子轨道理论).6.Topredictmoleculargeometries,N.V.Sidgwickproposedvalence-shellelectron-pairrepulsiontheory(VSEPR,“Vesper”)(价层电子对互斥理论)

in1940andthetheorywaslatermodifiedbyR.J.Gillespie.F.Hund(1896-1997)R.S.Mulliken(1896-1986)TheoryofChemicalBonding5.I§1.ValenceBondTheoryI.FormationofH2moleculesHeitlerandLondonsolvedtheSchrödingerequationforH2moleculesandfoundthatPotential-energycurveforH2Overlapoforbitals§1.ValenceBondTheoryI.Form《基础化学》英文教学课件：chapter_10§1.ValenceBondTheoryWhentwoHatomsaresomedistanceapart,thepotentialenergyoftheatomsarenearlyzero.WhentwoHatoms(withunpairedelectronsofsamespins)approachoneanother,thepotentialenergygetshigherandhigher,andthusnocovalentbondsareformed.WhentwoHatoms(withunpairedelectronsofoppositespins)approachoneanother,thepotentialenergygetslowerandlower,reflectingthebondingoftheatoms.Their1sorbitalsbegintooverlap(重叠),eachelectroncanthenoccupythespacearoundbothatoms.§1.ValenceBondTheoryWhen§1.ValenceBondTheoryThepotentialenergygetslower,reachesaminimumvalue,andthenincreases.Thedistance(74pm)betweennucleiatthisminimumenergyiscalledthebondlength(键长)ofH2.Thenatureofcovalentbond:Theorbitalofoneatomoverlapstheorbitalofanother,andthebondedelectronpairweresharedbybothnuclei.Theelectronsareattractedsimultaneouslybythepositivechargesofthetwonuclei.Theforcesthatholdtheatomstogethercanbeconsideredasarisingfromtheattractionofoppositelychargedparticles:nucleiandelectrons.§1.ValenceBondTheoryThepII.Valencebondtheory(价键理论)§1.ValenceBondTheoryValencebondtheory:Abondisformedbyoverlapoforbitalsfromtwoatoms.Anorbital(withunpairedelectron)ononeatomoverlaps(comestooccupyaportionofthesameregionofspace)withanorbital(withunpairedelectronwithoppositespin)ontheotheratom.II.Valencebondtheory(价键理论)§§1.ValenceBondTheoryThenumberofcovalentbondsformedforanatomislimitedbythenumberofunpairedelectronsintheatom(saturation,饱和性).H2();He2();Cl2();H2O();H3O();HCl().§1.ValenceBondTheoryThen§1.ValenceBondTheory

Strengthofbondingdependsontheamountofoverlap;thegreatertheoverlap,thegreaterthebondstrength.Orbitalsbondinthedirectioninwhichtheyprotrudeorpoint,toobtainmaximumoverlap(directionality,方向性).HCl§1.ValenceBondTheoryStrenIII.Typesofcovalentbond§1.ValenceBondTheory-bond:Thebondformedwhenatomicorbitalsthatcontainunpairedelectronsoverlapend-to-end(alongtheinternuclearaxis),ithasacylindricalshape(sausage)aboutthebondaxis.TheGreeklettersigma,,istheequivalentofletters.Itremindsusthat,lookingalongtheinternuclearaxis,theelectrondistributionresemblesthatofans-orbital.H2III.Typesofcovalentbond§1.§1.ValenceBondTheoryMuchthesamekindof-bondformationoccursinthehydrogenhalides(e.g.,HF).ForN2molecules,(only)oneofthethreeorbitalsoneachatomcanoverlapend-to-endtoforma-bond.HFN2§1.ValenceBondTheoryMuchthIII.Typesofcovalentbond§1.ValenceBondTheory-bond:Thebondformedwhenatomicorbitalsthatcontainunpairedelectronsoverlapside-by-side,ithasananti-symmetrical(反对称)distributionaboveandbelowthebondaxis.TheGreekletterpi,,istheequivalentofletterp.Whenweimaginelookingalongtheinternuclearaxis,a-bondresemblesapairofelectronsinap-orbital.III.Typesofcovalentbond§1.§1.ValenceBondTheoryAside-by-sideoverlapwillnotgivesostrongabondasanend-to-endoverlapoforbitals.Abondoccurswhentwoparallelorbitalsarestillavailableafterstrongbondshaveformed.§1.ValenceBondTheoryAside-§1.ValenceBondTheoryAsinglebondisa-bond.Adoublebondisa-bondplusone-bond.Atriplebondisa-bondplustwo-bonds.Multiplebonds1s2s2pN2NN§1.ValenceBondTheoryAsingl§1.ValenceBondTheoryCoordinatecovalentbond(配位共价键)Acovalentbondinwhichbothelectronscomefromoneoftheatomsiscalledcoordinatecovalentbond.Whenbondsformbetweenatomsthatbothdonateanelectron,Itispossibleforbothelectronstocomefromthesameatom,§1.ValenceBondTheoryCoordin§1.ValenceBondTheoryH+:NH3+:::N:HHHH+C:..O:..:+C:O:NH4+:CO:§1.ValenceBondTheoryH+:NH3+孔子曰：“益者三友，损者三友。友直，友谅，友多闻，益矣。友便辟(biànpì)，友善柔，友便佞(piánnìng)，损矣。”正直诚信恕人大度知识广博便辟(biànpì):谄媚(chǎnmèi)逢迎之人善柔：表面奉承而背后诽谤人之人便佞(piánnìng):善于花言巧语之人

孔子曰：“益者三友，损者三友。友直，友谅，友多闻，益矣。友便IV.Bondparameters(键参数)§1.ValenceBondTheorybondingpairlonepairBondingpair(成键电子对)

isanelectronpairsharedbetweentwoatoms.Lonepair(孤电子对,nonbondingpair)isanelectronpairthatremainsononeatomandisnotshared.Bondingpairsareoftenrepresentedbydashes:HClIV.Bondparameters(键参数)§1.V§1.ValenceBondTheory1.Bondlength(键长):

Thedistancebetweenthenucleiinabond.C-Cindiamond(154.2pm),inethane(153.3pm),inpropane(154pm),incyclohexane(153pm).Theaveragevalueis154pm.bondlengthl••§1.ValenceBondTheory1.Bond§1.ValenceBondTheory2.Bondorder(键级):

Thenumberofpairsofelectronsinabond.NNAsthebondorderincreases,thebondstrengthincreasesandthenucleiarepulledinward,decreasingthebondlength.Singlebond(C-C);Doublebond(C=C);Triplebond(CC).154pm134pm120pm§1.ValenceBondTheory2.Bond《基础化学》英文教学课件：chapter_10§1.ValenceBondTheoryExample10-1:Considerthemolecules,N2H4,N2,N2F2.Whichmoleculehastheshortestnitrogen-nitrogenbond?Whichhasthelongestnitrogen-nitrogenbond?Solution:Firstwritethestructuralformulas:Thenitrogen-nitrogenbondshouldbeshortestinN2,whereitisatriplebond,andlongestinN2H4,whereitisasinglebond.Experimentaldata:N2(109pm);N2H4(147pm).N2H4N2N2F2§1.ValenceBondTheoryExample§1.ValenceBondTheory3.Bondenergy(键能):TheenergythatmustbeaddedtoseparatetheatomsinH2moleculesiscalledthebonddissociationenergy(解离能).Itisessentiallytheenthalpychange(H)foragas-phasereactioninwhichabondbreaks.§1.ValenceBondTheory3.Bond§1.ValenceBondTheoryBondenergy:A-BbondenergyistheaverageenthalpychangeforthebreakingofanA-Bbondinamoleculeinthegasphase.§1.ValenceBondTheoryBonden§1.ValenceBondTheoryBondlengthandbondenergiesProtectivegas§1.ValenceBondTheoryBondle§1.ValenceBondTheoryBondenergyisperhapsofgreatestvaluewhenyoutrytounderstandtherelativestabilitiesofcompounds.Bondenergyisameasureofthestrengthofabond:thelargerthebondenergy,thestrongerthechemicalbond.Althoughadoublebondisstrongerthanasinglebond,itisnotnecessarilylessreactive.Ethylene,CH2=CH2,forexample,ismorereactivethanethane,CH3–CH3,wherecarbonatomsarelinkedthroughasinglebond.Thereactivityofethyleneresultsfromthesimultaneousformationofanumberofstrong,singlebonds.§1.ValenceBondTheoryBonden§1.ValenceBondTheory4.Bondangle(键角):

Theanglebetweentwobondsfromthesameatom.直线形V形平面三角形三角锥形四面体形平面四边形三角双锥形八面体形§1.ValenceBondTheory4.Bond§1.ValenceBondTheory5.Bondpolarity(键的极性)Acovalentbondinvolvesthesharingofatleastonepairofelectronsbetweentwoatoms.Whentheatomsarealike(theelectronegativityoftheatomsarethesame),thebondingelectronsaresharedequally.Thatis,theelectronsspendthesameamountoftimeinthevicinityofeachatom.Suchabondiscalledanonpolar(covalent)bond(非极性共价键).§1.ValenceBondTheory5.Bond§1.ValenceBondTheoryWhenthetwoatomsareofdifferentelements(differentelectronegativity),thebondingelectronsarenotsharedequally.Apolar(covalent)bond(极性共价键)isacovalentbondinwhichthebondingelectronsspendmoretimenearoneatomthantheother.NonpolarcovalentPolarcovalentIonic§1.ValenceBondTheoryWhenth§1.ValenceBondTheoryTheabsolutevaluesofthedifferenceinelectronegativityoftwoatomsgivesaroughmeasureoftherelativebondpolarities.Example10-2:Useelectronegativityvaluestoarrangethefollowingbondsinorderofincreasingpolarity:P—H,H—O,C—Cl.Solution:ElectronegativityvaluesareP(2.19),H(2.18),O(3.44),C(2.55),andCl(3.16),respectively.TheabsolutevaluesoftheelectronegativitydifferencesareP—H,0.01;H—O,1.26;C—Cl,0.61.Hence,theorderisP—H,C—Cl,H—O.§1.ValenceBondTheoryTheabs§1.ValenceBondTheoryDifferencesinelectronegativityexplains(1)whyionicbondsusuallyformbetweenametalatomandanonmetalatom,and(2)whycovalentbondsfromprimarilybetweentwononmetals.§1.ValenceBondTheoryDiffereI.Hybridorbitals(杂化轨道)§2.HybridOrbitalsThenumberofbondsformedbyagivenatomequalsthenumberofunpairedelectronsinitsvalenceshell?HClH2OCH2

1s2s2p3s3p1s2s2p1s2s2pCH4I.Hybridorbitals(杂化轨道)§2.H§2.HybridOrbitals1s2s2pExplanation:

Fourunpairedelectronsareformedwhenanelectronfromthe2sorbitalofthecarbonatomispromoted(excited)tothevacant2porbital.Itwouldrequireenergytopromotethecarbonatomthisway,butmorethanenoughenergywouldbeobtainedfromtheformationoftwoadditionalcovalentbonds.1s2s2pCatom(groundstate)Catom(excitedstate)§2.HybridOrbitals1s2s2pExpla§2.HybridOrbitalsThefourorbitalsofthecarbonatomcombineduringthebondingprocesstoformfournew,butequivalent(等价的),hybridorbitals.1ssp31s2s2pgroundstate1s2s2pexcitedstatehybridizedNuclearmagneticresonance(NMR)andinfraredspectroscopybothshowthatCH4hasfourequivalentC—Hbonds.§2.HybridOrbitalsThefouror§2.HybridOrbitalsTheshapeofasinglesp3hybridorbital(left).Thefourhybridorbitalsarearrangedtetrahedrallyinspace(right).Hybridorbitals

areorbitalsusedtodescribebondingthatareobtainedbytakingcombinationsofatomicorbitalsoftheisolatedatoms.§2.HybridOrbitalsTheshapeo§2.HybridOrbitalsOutlineofhybridorbitals

Onlyatomicorbitalswithapproximateenergyfromtheisolatedatomcanbecombinedtogivehybridorbitals,inwhichtheenergyandorientationoftheorbitalsareredistributed.Thenumberofhybridorbitalsformedalwaysequalsthenumberofatomicorbitalsused.Thereorientationofthehybridorbitalsisfavorableforthemaximumoverlapduringcovalentbondformation.Thereorientationofthehybridorbitalsminimizestherepulsionbetweenbondingelectronpairs,thustheresultingcovalentbondsaremorestable.§2.HybridOrbitalsOutlineofII.Typesofhybridorbitals§2.HybridOrbitals1.sphybridization(sp

杂化):BeCl2Cl——Be——ClDiagramofsphybridorbitals:Lineararrangement1s2s2pBe(groundstate)1sspBe(inBeCl2)1sspBe(hybridized)II.Typesofhybridorbitals§2§2.HybridOrbitals1s2s2p1ssp1sspBe(groundstate)Be(inBeCl2)Be(hybridized)Onlyoneofthethreeporbitalsareusedtoformsphybridorbitals.Thetwounhybridizedporbitalsisperpendicular(垂直的)totheaxisofthesphybridorbitalsandperpendiculartoeachother.§2.HybridOrbitals1s2s2p1ssp1§2.HybridOrbitals2.sp2hybridization:BF3BF3Diagramofsp2

hybridorbitals:Trigonalplanararrangement.1s2s2pB(groundstate)1ssp2B(inBeF3)1ssp2B(hybridized)§2.HybridOrbitals2.sp2hybr§2.HybridOrbitals1s2s2p1ssp21ssp2B(groundstate)B(inBeF3)B(hybridized)Onlytwoofthethreeporbitalsareusedtoformsp2hybridorbitals.Theunhybridizedporbitalisperpendicular(垂直的)

totheplaneofthesp2hybridorbitals.§2.HybridOrbitals1s2s2p1ssp2§2.HybridOrbitals3.sp3hybridization:CH4CH4Diagramofsp3

hybridorbitals:Tetrahedralarrangement.1s2s2pC(groundstate)1ssp3C(inCH4)1ssp3C(hybridized)§2.HybridOrbitals3.sp3hybr§2.HybridOrbitalsNH3?4.Nonequivalenthybridization(不等性杂化):H2O1s2s2pO(groundstate)1ssp3O-HbondslonepairsO(inH2O)1ssp3O(hybridized)H2O:Vshaped.Diagramofsp3

hybridorbitals:Tetrahedralarrangement.§2.HybridOrbitalsNH3?4.Non§2.HybridOrbitalsNH3:trigonalpyramidal.Diagramofsp3

hybridorbitals:Tetrahedralarrangement.1s2s2pN(groundstate)1ssp3N(hybridized)N(inNH3)1ssp3N-Hbondslonepair§2.HybridOrbitalsNH3:trigon5.Multiplebonds§2.HybridOrbitalsethyleneOnehybridorbitalisneededforeachbond(whetherasinglebondoramultiplebond)andforeachlonepair.1s2s2pC(groundstate)1ssp2C(inCH2CH2)1ssp2C(hybridized)5.Multiplebonds§2.HybridOr§2.HybridOrbitalsAsingle2porbitalstillremainsoneachCatom.Theseorbitalsareperpendiculartotheplaneofthehybridorbitals;thatis,perpendiculartothe–CH2plane.§2.HybridOrbitalsAsingle2p§2.HybridOrbitalsThecarbon-carbondoublebondcanbedescribedasonebondandonebond.Theformationofabond“locks”thetwo–CH2endsintoaflat,rigidmolecule.Whenthe–CH2planesrotatesothatthe2porbitalsbecomeparallel,theorbitalsoverlaptogiveabond.Thetwo–CH2planecanrotateabouttheC-Caxiswithoutaffectingtheoverlapofthehybridorbitals.Astheseplanesrotate,the2porbitalsalsorotate.§2.HybridOrbitalsThecarbon-§2.HybridOrbitals1s2s2p1ssp21ssp2?acetyleneC-HbondsC=CbondC=Cbond§2.HybridOrbitals1s2s2p1ssp2§2.HybridOrbitalsacetylene1s2s2p1ssp1sspC-HbondCCbondCCbonds§2.HybridOrbitalsacetylene1s§3.ValenceShellElectronPairRepulsionTheorytrigonalplanartrigonalpyramidalAsimplemodel,valenceshellelectronpairrepulsion(价层电子对互斥理论),canallowustopredictmoleculargeometries,orshapes.BF3PF3Valencebondtheoryprovidesaninsightintowhybondsformand,atthesametime,revealsthatbondshavedefinitedirectionsinspace.However,thistheorycanonlybeusedtoexplain

theexperimentaldata.§3.ValenceShellElectronPaiI.Valenceshellelectronpairrepulsion(VSEPR)theory§3.ValenceShellElectronPairRepulsionTheoryVSEPRmodel(pronounceas“vesper”)predictstheshapesofmoleculesandionsbyassumingthatthevalence-shellelectronpairsarearrangedabouteachatomsothatelectronpairsarekeptasfarawayfromoneanotheraspossible,thusminimizingelectron-pairrepulsions.I.Valenceshellelectronpair§3.ValenceShellElectronPairRepulsionTheoryII.StepstofollowinordertopredictthegeometryofanABnmoleculebytheVSEPRmethodMoleculargeometry(分子几何学):

Thegeneralshapeofamolecule,asdeterminedbytherelativepositionsoftheatomicnuclei.Notethedifferencebetweenthearrangementofelectronpairsandthemoleculargeometry.Thedirectioninspaceofthebondingpairsgivesyouthemoleculargeometry.§3.ValenceShellElectronPai§3.ValenceShellElectronPairRepulsionTheoryA:centralatom;B:ligand(配体).A,B:atomsofthemain-groupelements.ABnmolecule:Valenceshellelectronpair:Electronpairsof-bondsandloneelectronpairs.Electronpairsof-bondsarenotincluded.§3.ValenceShellElectronPai§3.ValenceShellElectronPairRepulsionTheory1.Determinehowmany(valence)electronpairsarearoundthecentralatom.II.StepstofollowinordertopredictthegeometryofanABnmoleculebytheVSEPRmethodLigandHandhalogenscontributeoneelectron,Ohasnocontribution;BF3,CO2.Thechargeonanionshouldbeconsidered,SO42-,NH4+;Centralhalogenatomcontributes7electrons,andoxygengroupatomcontributes6electrons;H2O.§3.ValenceShellElectronPai§3.ValenceShellElectronPairRepulsionTheory2.

Arrangetheelectronpairsasshowninlastslides.3.Obtainthemoleculargeometryfromthedirectionsofbondingpairs.Thenumberofelectronpairsisobtainedbydividingthenumberofelectronsby2.

Countamultiplebondasonepair.§3.ValenceShellElectronPaiIII.Moleculargeometry§3.ValenceShellElectronPairRepulsionTheoryCO2?O=C=O1.Twoelectronpairs(lineararrangement) Threeelectronpairs(trigonalplanararrangement)III.Moleculargeometry§3.Val2.Fourelectronpairs(tetrahedralarrangement)§3.ValenceShellElectronPairRepulsionTheory2.Fourelectronpairs(tetrah§3.ValenceShellElectronPairRepulsionTheoryExample10-3:Predictthegeometryofthefollowingmoleculesorions,usingtheVSEPRmethod:a.BeCl2;b.NO2-;c.SiCl4.Solution:a.BeCl2ThecentralBeatomhas2valenceelectrons,andeachClligandcontributesoneelectron.ThenumberofthevalenceelectronpairsonBeis(2+2)/2=2.ThetwopairsonBehavealineararrangement,indicatingalinearmoleculargeometryforBeCl2.§3.ValenceShellElectronPai§3.ValenceShellElectronPairRepulsionTheoryb.NO2-ThecentralNatomhas5valenceelectrons,Oatomsdonothavecontribution.Thecharge(-1)ontheionhavingconsidered,thenumberofvalenceelectronpairsonNis(5+1)/2=3.TheNatomhasthreevalenceelectronpairs,twoofwhicharebondingpairs.Therefore,themoleculargeometryoftheNO2-isbent.c.SiCl4ThecentralSiatomhas4valenceelectrons,andeachchlorinecontributesoneelectron.ThenumberofvalenceelectronpairsonSiis(4+4)/2=4,allofwhicharebonded.Therefore,themoleculargeometryoftheSiCl4istetrahedral.§3.ValenceShellElectronPai§3.ValenceShellElectronPairRepulsionTheory3.Fiveelectronpairs(trigonalbipyramidalarrangement)§3.ValenceShellElectronPai§3.ValenceShellElectronPairRepulsionTheory4.Sixelectronpairs(octahedralarrangement)§3.ValenceShellElectronPai§3.ValenceShellElectronPairRepulsionTheoryExample10-4:AccordingtotheVSEPRmodel,whatmoleculargeometrywouldyouexpectforiodinetrichlorideICl3?Solution:ThecentralIatomhas7valenceelectrons,andeachchlorinecontributesoneelectron.ThenumberofvalenceelectronpairsonIis(7+3)/2=5,threeofwhicharebondingpairs.Therefore,themoleculargeometryoftheICl3isT-shaped.§3.ValenceShellElectronPai§3.ValenceShellElectronPairRepulsionTheory1.Alonepairtendstorequiremorespacethanacorrespondingbondingpair.2.

Multiplebondsrequiremorespacethansinglebondsbecauseofthegreaternumberofelectrons.Notes:AlimitationoftheVSEPRmodelisthatitcannotexplainwhybothCH2groupslieinthesameplane.§3.ValenceShellElectronPaiI.Dipolemoment(偶极矩)§4.IntermolecularForcesThepolarityofabondischaracterizedbyaseparationofelectriccharge(电荷分离).WecanrepresentthisinHClbyindicatingpartialcharges,q+andq-,ontheatoms.

nonpolarbond

polarbondH—Cl+-H—Cl+-qqRed:negativecharge;Blue:positivecharge.I.Dipolemoment(偶极矩)§4.Inte§4.IntermolecularForcesAnymoleculethathasanetseparationofchargehasdipolemoment(偶极矩).Amoleculeinwhichthedistributionofchargeisequivalenttochargesq+andq-separatedbyadistancedhasadipolemomentequalto:TheSIunitofdipolemomentis1C·m(1coulomb-meter).Itisthedipolemomentofachargeof1Cseparatedfromacharge–1Cbyadistanceof1m.§4.IntermolecularForcesAnym§4.IntermolecularForcesAcommonly-usedunitofdipolemomentisdebye(D),namedfortheDutchchemistPeterDebye,whomadeimportantstudiesofdipolemoments.Thedebye(D)isdefinedsothatasinglenegativecharge(anelectron)separatedby100pmfromasinglepositivecharge(aproton)hasadipolemomentof4.80D.1D=3.336×10-30C·m.§4.IntermolecularForcesAcom§4.IntermolecularForcesApolarmolecule(极性分子)

isamoleculewithanonzerodipolemoment;II.Polarityofmolecules1.Alldiatomicmoleculesarepolariftheirbondsarepolar.Alldiatomicmoleculesthatarecomposedofatomsofdifferentelements,suchasHClandCO,arepolar.Allhomonucleardiatomicmolecules,suchasO2,N2,andCl2,arenonpolar.Anonpolarmolecule(非极性分子)

isamoleculethathasazerodipolemoment.§4.IntermolecularForcesApol§4.IntermolecularForces2.Forpolyatomicmolecules,itisimportanttodistinguishbetweenapolarmoleculesandapolarbond.1.CO22.H2O3.C2H2Cl24.C2H2Cl25.CCl46.CHCl3Red:negativecharge;Blue:positivecharge.123456§4.IntermolecularForces2.Fo§4.IntermolecularForcesThosegeometriesinwhichtheBatomstendtobeononesideofthemolecule(forexample,bent,trigonalpyramidal,T-shaped,seesaw,andsquarepyramidal)canhavenonzerodipolemoments;thatis,theycangivepolarmolecules.ThegeometriesofABnmoleculesinwhichA—Bbondsaredirectedsymmetricallyaboutthecentralatom(中心对称)(forexample,linear,trigonalplanar,tetrahedral,andoctahedral)givemoleculesofzerodipolemoment;thatis,themoleculesarenonpolar.§4.IntermolecularForcesThose§4.IntermolecularForcesFormulaMolecularGeometryDipoleMomentAB2AB3zerocanbenonzerozerocanbenonzerocanbenonzerolinearbenttrigonalplanartrigonalpyramidalT-shaped§4.IntermolecularForcesFormu§4.IntermolecularForcesFormulaMolecularGeometryDipoleMomentAB4zerozerocanbenonzerotetrahedralsquareplanarseesaw§4.IntermolecularForcesFormu§4.IntermolecularForcesFormulaMolecularGeometryDipoleMomentAB5zerocanbenonzerozeroAB6trigonalbipyramidalsquarepyramidaloctahedral§4.IntermolecularForcesFormu§4.IntermolecularForcesDipolemoments/(10-30C·m)ofsomemolecules§4.IntermolecularForcesDipol§4.IntermolecularForcesLeft:Waterisapolarliquid,itisattractedtotheelectricallychargedrod.Right:CCl4isanonpolarliquid,itisnotattractedtotheglassrod.AttractionofapolarliquidtoanelectrifiedrodH2OCCl4§4.IntermolecularForcesLeft:§4.IntermolecularForcesIII.Polarizationofmolecules(分子的极化)Polarization:Thephenomenonthatthedipoleofamoleculecanbeinducedorchangedbyanelectricfield.PermanentdipoleInduceddipole§4.IntermolecularForcesIII.§4.IntermolecularForces1.Polarizationcannotonlyoccurinanelectricfield,butalsohappenduetotheinteractionsamongmolecules.Notes:2.Morepolarizable(可极化的):smallorlargemolecules?

He,Ne,andAr?Largeratoms(molecules)aremoreeasilydistortedbecausetheelectronsarefartherfromthenuclei.§4.IntermolecularForces1.PIV.VanderWaalsforces(范德华力)§4.IntermolecularForcesvanderWaalsforcesareageneraltermforintermolecularforces.Theyincludesorientationforces(取向力,

dipole-dipoleforces),inductionforces(诱导力),anddispersionforces(色散力,Londonforces).Intermolecularforcesaretheforcesofinteractionbetweenmolecules.Theseforcesarenormallyweaklyattractive.J.D.vanderWaals(1837-1923)NetherlandsNobelprizeforPhysics(1910)IV.VanderWaalsforces(范德华力§4.IntermolecularForcesvanderWaalsforcesarenamedfortheDutchphysicistJohannesvanderWaalswhowasthefirsttosuggesttheimportanceofintermolecularforcesandusedtheconcepttoderivehisequationforgases.§4.IntermolecularForcesvand§4.IntermolecularForcesOrientationforces(dipole-dipoleforce):Anattractiveintermolecularforceresultingfromthetendencyofpolarmoleculestoalignthemselvessuchthatthepositiveendofonemoleculeisnearthenegativeendofanother.1.Orientationforces(取向力)solidliquidHCl§4.IntermolecularForcesOrien§4.IntermolecularForcesDispersionforces(Londonforces):Theweakattractiveforcesbetweenmoleculesresultingfromthesmall,instantaneous