吉林大学材料科学基础2

AtomicStructureandInteratomicBondingChapter2Whystudyatomicstructureandinteratomicbonding?Someofimportantpropertiesofmaterials2.1Introduction

Atomicstructure—geometricalatomicarrangements

Atypeofinteratomicbondingondepend2Tobeconsidered:Severalfundamentalandimportantconcept,namely:Atomicstructure①②Electronconfigurationsinatoms③Periodictable(周期表)Varioustypesofprimaryandsecondaryinteratomicbondsthatholdtogethertheatomscomprisingasolid.1AtomNucleusElectrons(9.1110-31kg,1.6010-19C)Protons(+1.6010-19C)Neutrons(1.6710-27kg)2.2FundamentalconceptsForachemicalelement,the

numberof

protonswithintheatomicnucleus.theatomicnumber(Z,原子序数)Zrangesfrom1(H)to92(U:thehighestofthenaturallyoccurringelements).characterizeeachchemicalelementForanelectricallyneutralorcompleteatom,thenumberofprotons=thenumberofelectronsatomsofthesameelementthathavedifferentatomicmasses.thenumberofneutrons(N)maybevariable.Isotopes(同位素)maybeexpressedasthesumofthemassesofprotonsandneutronswithinthenucleus.Atomicmass(A)Theweightedaverageoftheatomicmassesofanatom’snaturallyoccurringisotopes.Atomicweight(原子量)Atomicmassunit(amu)Mole:Thequantityofasubstancecorrespondingto6.023

1023atomsormolecules.1amu/atom(ormolecule)=1g/mol1amu:oftheatomicmassofthemostcarbon12(12C,A=12.00000)commonisotopeofcarbon—e.g.:Fe—55.85amu/atom,or55.85g/mol2.3ElectronsinatomsAtomicModelsAbranchofphysicsthatdealswithatomicandsubatomicsystems;itallowsonlydiscretevaluesofenergy

thatareseparatedfromoneanother.Bycontrast,forclassicalmechanics,continuousenergyvaluesarepermissible.Quantummechanics(量子力学)OneearlyoutgrowthofquantummechanicswassimplifiedBohratomicmodel(波尔原子模型)玻尔NielsHenrikDavidBohr(1885~1962)Danishphysicist.生于哥本哈根1911年在剑桥大学卡文迪什实验室工作。1912年在曼彻斯特卢瑟福实验室工作。玻尔的卓越贡献是1913年提出玻尔原子模型，成功地解释了氢原子光谱玻尔的理论圆满地解释了元素的周期性。他把化学推进到更深的层次，使物理和化学这两门学科统一到同一量子理论基础上来。玻尔原子模型的提出，是原子结构理论发展史上一个里程碑。虽然自原子的波动力学模型出现以后，玻尔原子模型已经过时，但其结果在定性方面还是正确的。第二次世界大战期间，玻尔带着铀核可分裂的情报，到美国参加原子弹的研制工作。战后，他致力于原子能的和平利用。他因在研究原子结构和辐射方面的贡献而获1922年诺贝尔物理学奖。1、Electronsareassumedtorevolvearoundthenucleusindiscreteorbitals(position).twoimportantprinciple2、Energiesofelectronsarequantized;electronsarepermittedtohaveonlyspecificvaluesofenergy(energy).

Fig.2.1SchematicrepresentationoftheBohratom.

Thatis,adjacentstatesareseparatedbyfiniteenergiesnucleusOrbitalelectron—Energylevelsorstates（能级、能态）allowedelectronenergiesabsorptionofenergy：Energy110-18210-182s2pn=2n=33s3p3dn=12s(a)(b)Fig.2.2(a)ThefirstthreeelectronenergystatesfortheBohrhydrogenatom.(b)Electronenergystatesforthefirstthreeshellsofthewave-mechanicalhydrogenatom.quantumjump

absorptionofenergy

emissionofenergyWave-mechanicalmodel:Atomicmodelinwhichtheelectronisconsideredtoexhibitbothwavelikeandparticle-likecharacteristics.Thepositionofelectroninatomsisconsideredtobetheprobabilityofanelectron’sbeingatvariouslocationsaroundthenucleus.Inotherwords,positionisdescribedbyaprobabilitydistributionorelectroncloud.DistancefromnucleusorbitalelectronnucleusProbability1.00(a)(b)Fig.2.3Comparisonofthe(a)Bohrand(b)wave-mechanicalatommodelsintermsofelectrondistribution.Quantumnumbers(量子数)Asetoffournumbers,whichcharacterizepossibleelectronstatesinanatom

Specifyelectronshells(),

whichisrelatedtothedistanceofanelectronfromthenucleus,oritsposition

whichonly,isalsoassociatedwiththeBohrmodel.1、Principalquantumnumber(n)主量子数

Takeonintegralvaluesbeginningwithunity,n=1,2,3,4,5…;

sometimestheseshellsaredesignatedbythelettersK,L,M,N,O…;MNOPQKL

signifiesthesubshell,whichisrelatedtotheshapesoftheelectronsubshell

whichisrestrictedbythemagnitudeofn,l=0,1,2,…,(n-1);

whichisdenotedbyalowercaseletter—s(l=0),p(l=1),d(l=2),orf(l=3)…;

2、Azimuthalquantumnumber(l)角量子数spd

whenamagneticfieldisapplied,thesesubshellstatessplit,mldeterminesthenumberofenergystatesforeachsubshell

mlstartsatnegativel,runsbywholenumberstozeroandthengoestopositivel,ml=

l,

l+1,…0,…l

1,+l;

Intheabsenceofan

externalmagneticfield,thestateswithineachsubshellareidentical.3、Magneticquantumnumber(ml

)磁量子数l=0,ml=0asingleenergystate

l=2,ml

=

2,

1,0,+1,+2

denotingfivespatialorientationl=1,ml

=1,0,1

threestatesexist,denotingthreespatialorientationpxpypzdxzdxydyzSpatialorientationshapesizeofelectron’sprobabilitydensityThreeofthesequantumnumbersn,l,mldescribeTheBohrmodelwasfurtherrefinedbywavemechanics,inwhichtheintroduction

ofn,l,mlgivesrisetoelectronsubshellswithineachshell.

Associatedwitheachelectronisaspinmoment,whichmustbeorientedeitherupordown.afterthen,landmltobeusedhavebeendetermined,assignthevalue+1/2tooneelectron,thenassign-1/2tothenextelectron,whileusingthesamen,landmlvalues.Theruleforselectingmsisasfollows:4、Spinquantumnumber(ms

)自旋量子数Table2.1thenumberofavailableelectronstatesinsomeoftheelectronshellsandsubshellsFig.2.4Schematicrepresentationoftherelativeenergiesoftheelectronsforthevariousshellsandsubshells.Energy

spsspspspddfspfdspfdPrincipalquantumnumber,n

1234567dSeveralfeaturesofthediagramareworthnoting:1、thesmallerthen,thelowertheenergylevel;

Forexample,1s<

2s<3s2、withineachshell,theenergyofasubshelllevelincreaseswiththevalueofthel;

Forexample,3s<3p<3d3、theremaybeoverlapinenergyofastateinoneshellwithstatesinanadjacentshell,whichisespeciallytrueofdandfstates;

Forexample,3d>4sElectronconfigurations(电子组态、电子排布)Electronstates(level)☞Valuesofenergythatarepermittedforelectrons.Intheatomiccaseeachstateisspecifiedbyn,l,ml,ms

ofanatomrepresentsthemannerinwhichthesestatesareoccupiedshell

subshell

numberofelectrons(byasuperscript)Notation:

Electronsenterandfillthesestatesaccordingtofourrules1、Pauliexclusionprinciple(泡利不相容原理)Eachelectronstatecancontainamaximumoftwoelectrons,whichmusthaveoppositespins.s,p,d,andf—atotalof2,6,10,and14electronsThus,2、AufbauorBuild-upprinciple(能量最低原理)Theelectronsfillupthelowestpossibleenergystatesintheelectronshellsandsubshells,twoelectrons(havingoppositespins)perstate.groundstate(基态)anormallyfilledelectronenergystatefromwhichelectronexcitationmayoccur.Fig.2.5Schematicrepresentationofthefilledenergystatesforasodiumatom(Na).Increasingenergy1s2s2p3s3p1s22s22p63s1ElectronconfigurationofNaatom:3、Hund’sRule(洪特规则)whentherearedegenerateorbitals

(简并轨道)available,electronswillentertheorbitalsone-at-a-timetomaximisedegeneracyB1s22s22px1—C1s22s22px12py1—N1s22s22px12py12pz1—O1s22s22px22py12pz1—F1s22s22px22py22pz1—Ne1s22s22px22py22pz2

—1)

泡利不相容原理：

同一原子中，不可能有四个量子数完全相同的两个电子。因此，同一轨道只能容纳两个自旋相反的电子。原子核外电子的分布原则2)

能量最低原理：

基态原子中，电子是尽先占据能量最低的原子轨道。3)

洪特规则：等价(简并)轨道上的电子，将尽先分占不同轨道而且自旋平行。saystheorbitalfillintheordern+0.7l

(lowestfirst).Thisgivesthesequence8s7p6d5f7s6p5d4f6s5p4d5s4p3d4s3p3s2p2s1sOrbitalenergy1.02.02.73.03.744.44.75.05.45.76.06.16.46.77.07.17.47.78.0Lowestenergiesfillfirst1s2s2p3s3p4s3d4p5s4d5p6s4f5d6p7s5f6d7p8s4、徐光宪’sRuleTable2.2AlistingoftheexpectedelectronconfigurationsforsomeofthecommonelementsValenceelectrons(价电子)thosethatoccupytheoutermostfilledshell.Extremelyimportant

Theyparticipateinthebonding

betweenatomstoformatomicandmolecularaggregates.

Furthermore,manyofthephysicalandchemicalpropertiesofsolidsarebasedonthesevalenceelectrons.StableelectronconfigurationsWhicharevirtuallyunreactivechemicallyThestateswithintheoutermost

orvalenceelectronshellarecompletelyfilled.Theunfilledvalenceshellsassumestableelectronconfigurationsbygainingorlosingelectronstoformchargedions,orbysharingelectronswithotheratoms.inert,ornoblegases

惰性气体helium(He):1s2neon(Ne):1s22s22p6argon(Ar):[Ne]3s23p6krypton(Kr):[Ar]4s24p6hybridorbitals(杂化轨道)underspecialcircumstances,thes,panddorbitalscombinetoformhybridspn(n:thenumberofporbitalsinvolved,1,2,or3)

ors-p-d

orbitals.F:1s22s22p5

Be:1s22s2

Whatwouldhybridizetheorypredictaboutthemolecularstructure?

Thereisanunpairedelectronina2porbital

Thisunpaired2pelectroncanbepairedwithanunpairedelectronintheBeatomtoformacovalentbondsphybridorbitals—e.g.BeF21)promoteavalenceelectronfromthegroundstateconfigurationtoahigherenergyorbital2)hybridizetheappropriatevalenceelectronorbitalstoachievethedesiredvalenceelectrongeometry(i.e.thecorrectnumberofhybridorbitalsfortheappropriatevalenceelectrongeometry)whenconstructinghybridorbitals,thetwostepsoftenobservedBe:twosphybridorbitalsBondingorbitaloverlapF2porbitalssp2hybridorbitals—e.g.BF3B:1s2p2spromotehybridize1ssp22psorbitalporbitalssp2

hybrid

orbitals(trigonalplanar)1s2s2psp3hybridorbitals—e.g.CH4hybridizesorbitalporbitalssp3

hybrid

orbitals(tetrahedral)promotehybridizeC:1s2p2s1s2s2p1ssp3HHHHsp3hybridorbitals—e.g.H2OhybridizeO:1s2p2s1ssp3lonepairs(孤对电子)availableforbondingsorbitalporbitalssp3

hybrid

orbitals(tetrahedral)hybridizeN:1ssp3lonepairsavailableforbondingsorbitalporbitalssp3

hybrid

orbitals(tetrahedral)hybridizesp3hybridorbitals—e.g.NH31s2p2shybridizepromoteHybridizationinvolvingdorbitalse.g.—[FeF6]3-Fe3+：

hybridizesp3d24d3dbondingsp3d2

hybrid

orbitals(octahedral)F

F

F

F

F

F

Fe杂化键合Hybridizationinvolvingdorbitalse.g.—[Fe(CN)6]3-重排Fe3+：

rearrangement3d4s4phybridize3dd2sp3bondingCN

CN

CN

CN

CN

CN

杂化键合The3A,4A,and5Agroupelementsoftheperiodictablearethosewhichmostoftenformhybrid.Thedrivingforceisalowerenergystateforthevalenceelectrons.ValenceelectronpairgeometryNumberoforbitalsHybridOrbitalslinear2spTrignalplanar3sp2tetrahedral4sp3octahedral6sp3d2Thearrangementofthechemicalelementswithincreasingatomicnumberaccordingtotheperiodicvariationinelectronstructure.Nonmetallicelementsarepositionedatthefarright-handsideofthetable.2.4TheperiodictableGroupsorcolumn(118族)Thehorizontalrowsiscalled

Periods(17周期)Theverticalrowsiscalled.Allelementsthatarearrayedinagivengrouphavesimilarvalenceelectronstructure,aswellaschemicalandphysicalproperties.1stPeriod:1s1—2elements—

1s22ndand(3)rdPeriod:

2(3)s12—8elements—2(3)p164thand(5)thPeriod:

4(5)s12

3(4)d1

10

18elements4(5)p1

66thPeriod:6s12—5d1—4f1

14—5d10—

6p1

67thPeriod:7s1—6d1—5f1

14—6d10

therightmostgroup,

positionedinGroup0,

whichhavefilledelectronshellsandstableelectronconfigurations.Inertgases(惰性气体)He、Ne、Ar、Kr、Xe、Rn

氦、氖、氩、氪、氙、氡

positionedinGroupVIIA,

oneelectrondeficientfromhavingstablestructures,halogens(卤素)

positionedinGroupVIA

twoelectronsdeficientfromhavingstablestructures,Thealkalimetals(碱金属)andthealkalineearthmetals(碱土金属)

positionedinGroupIAandIIA

oneandtwoelectronsinexcessofstable,ns1~2Theelementsinthethreelongperiods,GroupsIIIBthroughIIBwhichhavepartiallyfilleddelectronstatesandinsomecasesoneortwoelectronsinthenexthigherenergyshellTransitionmetals(过渡金属)4Period5Period6PeriodMetalloids(准金属)

GroupsIIIA,IVA,andVA(B,Si,Ge,As,etc.)

displaycharacteristicsthatareintermediatebetweenthemetalsandnonmetalsbyvirtueoftheirvalenceelectronstructure

theyarecapableofgivinguptheirtheirfewvalenceelectronstobecomepositivelychargedions.

Also,atermusedtodescribemetallicelements.(mostoftheelementsreallycomeunder(归入)themetalclassification.)Electropositive(正电性)elements

howwillingatomsaretoacceptelectrons

Also,atermusedtodescribenonmetallicelements.Subshellswithonemissingelectron—highelectronegativityElectronegative(负电性)elementselectronegativityincreasesinmovingfromlefttorightandfrombottomtotopFig.2.7Theelectronegativityvaluesfortheelements.AddYourTextAddYourTextAddYourTextAddYourText2.5BondingforcesandenergiesPhysicalpropertiesofmaterialsInteratomicforce(F):thatbindtheatomictogetherwhichhavetwotypes——attractive(FA)andrepulsive(FR)thenetforceFN=FA+FR

FA(FR)=f(r);r:theseparationorinteratomicdistanceTwoisolatedatoms(孤立原子)AtlargedistanceInteractionsarenegligibleAstheatomsapproachEachexertsforcesontheotherWhenFA

andFRbalance,FA+

FR=0Thereisnonetforce,thenastateofequilibriumexistFig.2.8Thedependenceofrepulsive,attractive,andnetforcesoninteratomic

separation(r)(原子间距)fortwoisolatedatoms.(b)Thedependenceofrepulsive,attractive,andnetpotentialenergiesonrfortwoisolatedatoms.repulsionForceFAttrction0+

AttractiveforceFA(吸引力)InteratomicseparationrRepulsiveforceFRNetforceFNr0(a)(b)Attrctionrepulsion+0

PotentialenergyEE0NetenergyENAttractiveenergyEAInteratomicseparationrRepulsiveenergyER(排斥能)Formanyatoms,r0

0.3nm(3Å)CorrespondstotheseparationdistanceattheminimumofthepotentialenergycurveOnceatr0,thetwoatomswillcounteractanyattempttoseparatethembyanattractiveforce,ortopushthemtogetherbyarepulsiveactionEquilibriumspacing(平衡间距)r0

★Itcanbethoughtofasenergystoredwithinaphysicalsystem.★Itiscalledpotentialenergybecauseithasthepotentialtobeconvertedintootherformsofenergy,suchaskineticenergy,andtodoworkintheprocess.★ItiscloselylinkedwithforcesPotentialenergy(势能)EmathematicallyOr,foratomicsystemsorWecancheckF(x)=

kx(胡克定律)F(x)=

mg(重力)☞~istheregionsurroundingalocalminimumofpotentialenergy.☞Energycapturedinapotentialwellisunabletoconverttoanothertypeofenergybecauseitiscapturedinthelocalminimumofapotentialwell.Potentialenergytroughorwell(势阱)☞Theamountofenergylostatthepointofminimumenergyisthe~☞itrepresentstheenergythatwouldberequiredtoseparatethesetwoatomstoaninfiniteseparation.E0,thecurveshape,andbondingtypeanumberofmaterialpropertiesdetermineBondingenergy(结合能)E0Forexample：☞

bondingenergies

meltingtemperatures

;

solid>liquids>gaseousstate☞

TherelationshipbetweencurveshapeandmechanicalstiffnessSteepslope:relativelystiffShallowerslope:relativelyflexibleStronglybondedWeaklybondedSeparationr0ForceFF-versus-rcurveThetypeofbondPrimaryinteratomicbonds第一类(化学)键Secondarybonds第二类(物理)键ioniccovalentmetallicvanderWallshydrogen2.6primaryinteratomicbondsIonicbonding(离子键)OppositesidesoftableMetalandnonmetalElectropositiveandelectronegativeDonated(transferred)electronNa(metal)unstableCl(nonmetal)unstableNa(cation)stable[Ne]Cl(anion)stable[Ar]CoulombicattractionNucleusValenceelectrontransferFig.2.9Schematicrepresentationofionicbondinginsodiumchloride(NaCl)CoulombicbondingforceBondingenergy600~1500kJ/mol(3and8eV/atom),Nondirectional(无方向性)bond,Electricallyandthermallyinsulative,Transparent,brittle,highmeltingtemperature.Abovepropertiesareadirectconsequenceofelectronconfigurationsand/orthenatureoftheionicbond.generalcharacteristicstheattractiveenergyrepulsiveenergy2.82.9Fortwoisolatedions:A,B,andn(8)areconstants;dependontheparticularionicsystemThepredominantbondinginceramicmaterialsisionic.Covalentbonding(共价键)NearontableSimilarelectronegativitiesSharedvalenceelectronFig.2.10Schematicrepresentationofcovalentbondinginamoleculeof

methane(CH4)SharedelectronfromcarbonSharedelectronfromhydrogen