材料科學導論第二章原子鍵

材料科學導論

IntroductiontoMaterialsScienceDepartmentofEnvironmentalandChemicalEngineering,NanchangHangkonguniversityFumaoshengChapter2/AtomicstructureandinteratomicbondingLearningobjectives：Whycantheatomsbondtogetherandcompriseasolid?Howmanybondingtypesarethereinmaterials？Whatarethecloseinterrelationshipsbetweenpropertiesofmaterialsandtheirbondingtypes本章基本要求教學目的：從原子結構、結合鍵的不同層次去認識材料本質,加深對材料結構與成分與性能之間的關系的理解。主要內(nèi)容：了解原子結構對原子間結合鍵和材料性能的影響,掌握原子間的結合鍵種類及其各自特點,以及它們對材料性能的影響。重點與難點：

重點：原子間的結合鍵種類及其各自特點。

難點：原子間的結合鍵對材料性能的影響教學方法與手段授課方式：講課、講座、課堂討論、自學

教學手段：多媒體授課課時安排：2主要講述內(nèi)容2.1、Atomicstructure原子結構2.2、Interatomicbonding原子間結合鍵

材料的結構鍵合結構晶體結構組織結構原子間的結合鍵結構原子或分子排列結構宏觀組織和顯微組織結構原子結構原子中的電子結構晶體：原子排列長程有序，有周期

晶體結構非晶體：原子排列短程有序，無周期準晶體：原子排列長程有序，無周期定義：組成材料的不同物質表示出的某種形態(tài)特征組織結構勻晶型組織共晶型組織包晶型組織相圖特征結構特征馬氏體組織奧氏體組織貝氏體組織…...組合特征單相組織兩相組織多相組織…...結構分析2ATOMICSTRUCTUREANDBONDINGGold:FCC用掃描遂道顯微鏡觀察原子的排列情況掃描隧道顯微鏡像在掃描隧道顯微鏡下，在硅（111）表面直接取出原子而“刻寫”出平均線寬為2納米的字體。2.1AtomicStructure

ATOMICSTRUCTUREANDINTERATOMIC

BONDING2決定著材料絕大部分性能的最小因素原子結構1）Bohratomicclassicalmodel玻爾模型

ATOMICSTRUCTUREANDINTERATOMIC

BONDING2優(yōu)點：能定性地解釋原子的穩(wěn)定性即定態(tài)規(guī)則（定態(tài)的存在）和線狀原子光譜缺點：它不能解釋電子衍射現(xiàn)象,因為它仍然是將電子視為服從牛頓力學的經(jīng)典粒子。

1.Electronorbitals2.Quantizedenergy2ATOMICSTRUCTUREANDBONDING2）Wave-Mechanicsmodel波動力學模型電子和一切微觀粒子都具有二象性，即既具有粒子性(particle-like)

，又具有波動性(wavelike)。

ATOMICSTRUCTUREANDINTERATOMIC

BONDING22、Wave-Mechanicsmodel波動性:電子某一瞬時在某一位置的幾率(即可能性Probability)圖2.3玻爾模型和波動力學模型比較

ATOMICSTRUCTUREANDINTERATOMIC

BONDING2科學的描述體系物理模型（物理參數(shù)）量子數(shù)每一個電子的能級可由四個量子數(shù)確定

ATOMICSTRUCTUREANDINTERATOMIC

BONDING2薛定諤方程schrodingerequation方程中引入波函數(shù)的概念，以取代經(jīng)典物理中的圓形的固定軌道，解得的波函數(shù)（習慣上又稱原子軌道）描繪了電子在核外空間各處的位置出現(xiàn)的幾率，相當于給出了電子運動的“軌道”。Atomicstructure——electronarrangementFourquantumnumbers

ATOMICSTRUCTUREANDINTERATOMIC

BONDING2主量子數(shù)(Principalquantumnumber)n表示電子所處的量子殼層shell，為正整數(shù)1，2，3，。。。n值是確定電子離核遠近和能級的主要參數(shù)1角量子數(shù)l

(azimuthalquantumnumber)l值基本反映原子軌道的形狀l=0,1,2,…,n-1.n為主量子數(shù)。例如：n=2,l=0,1角量子數(shù)往往用字母表示，l=0s能級l=1p能級l=2d能級l=3f能級2自旋量子數(shù)ms

(spinquantumnumber)表示電子的自旋方向，ms=+1/2,-1/24磁量子數(shù)mL

(magneticquantumnumber)m值基本反映原子軌道的空間取向.磁量子數(shù)mL給出每個角量子數(shù)的能級數(shù)（軌道數(shù)），為-l,+l之間的整數(shù)例如：l=2,則mL=-2，-1，0，1，2，（共2l+1個）32ATOMICSTRUCTUREANDBONDINGElectronconfiguration核外電子組態(tài)Todeterminethemannerinwhichelectronsstatesarefilledwithelectronsoutsideofnucleus,threeprinciplesarefollowedthelowestpossibleenergylawPauliExclusionPrincipleHundlaw

ATOMICSTRUCTUREANDINTERATOMIC

BONDING22ATOMICSTRUCTUREANDBONDING2ATOMICSTRUCTUREANDBONDINGElectronconfigurationforsodiumNa1s22s22p63s1theperiodicstableofelements2ATOMICSTRUCTUREANDBONDING2.2、Interatomicbonding

原子間結合鍵Thenetforcebetweenapairofoppositelychargedionsisequaltothesumoftheattractiveandrepulsiveforces.

Fnet=Fattractive+Frepulsive2.2.1Bondingforcesandenergies2ATOMICSTRUCTUREANDBONDINGFIGURE2.11Forcevs.separationdistanceforapairofoppositelychargedions.Theequilibriuminterionicseparationdistancea0isreachedwhentheforcebetweentheionsiszero

r0ora0:平衡距離2ATOMICSTRUCTUREANDBONDING

r0ora0:平衡距離TheirmagnitudeofFN,FA,FRvarywiththedistance2ATOMICSTRUCTUREANDBONDING2.2.2interatomicbondtypesClassificationofinteratomicbondsPrimaryinteratomicbonds主原子結合鍵SecondarybondingorVanderWaalsbonding次原子間結合鍵原子結構金屬鍵共價鍵離子鍵范德華鍵原子原子鍵聚集體

ATOMICSTRUCTUREANDINTERATOMIC

BONDINGprimaryatomicbonds離子鍵1.IONICBONDING離子鍵價電子的完全貢獻或獲得2ATOMICSTRUCTUREANDBONDINGFormationofasodiumchlorideionpairfromsodiumandchlorineatoms.Intheionizationprocessa3s1electronfromthesodiumatomistransferredtoahalf-empty3porbitalofthechlorineatom.原子間距及結合能Coulombicbondingforce:靜電庫侖力

Ionicbondingistermednondirectional,thatis,themagnitudeofthebondisequalinalldirectionsaroundanion.Itfollowsthatforionicmaterialstobestable,allpositiveionsmusthaveasnearestneighborsnegativelychargedionsinathree-dimensionalscheme,andviceversa.Thepredominantbondinginceramicmaterialsisionic.Incovalentbondingstableelectronconfigurationsareassumedbythesharingofelectronsbetweenadjacentatoms.Twoatomsthatarecovalentlybondedwilleachcontributeatleastoneelectrontothebond,andthesharedelectronsmaybeconsideredtobelongtobothatoms.CovalentbondingisschematicallyillustratedinFigure2.10foramoleculeofmethane(CH4).2.COVALNETBONDING共價鍵2ATOMICSTRUCTUREANDBONDING價鍵理論共價鍵數(shù)個原子共享部分電子，有方向性分子軌道理論2ATOMICSTRUCTUREANDBONDING2s22p5(share1p)2s22p4(share2p)2s22p3(share3p)DirectionalSaturational.

Characteristicofcovalentbond2ATOMICSTRUCTUREANDBONDING

Covalentbond

maybeverystrong,asindiamond;ortheymaybeveryweak,aswithbismuth.Materialsareelectricallyandthermallyinsulative,becauseofnoneproductionofelectronsmovingeasily.人們對金屬晶體中的電子狀態(tài)的認識經(jīng)歷了一個從經(jīng)典自由電子論(即特魯?shù)履Ｐ?到現(xiàn)代能帶理論的發(fā)展過程3.METALLICBONDING2ATOMICSTRUCTUREANDBONDING經(jīng)典自由電子論(即特魯?shù)履Ｐ?Metallicbonding,thefinalprimarybondingtype,isfoundinmetalsandtheiralloys.Arelativelysimplemodelhasbeenproposedthatverynearlyapproximatesthebondingscheme.Metallicmaterialshaveone,two,oratmost,threevalenceelectrons.Withthismodel,thesevalenceelectronsarenotboundtoanyparticularatominthesolidandaremoreorlessfreetodriftthroughouttheentiremetal.Theymaybethoughtofasbelongingtothemetalasawhole,orforminga‘‘seaofelectrons’’oran‘‘electroncloud.’’Theremainingnonvalenceelectronsandatomicnucleiformwhatarecalledioncores,whichpossessanetpositivechargeequalinmagnitudetothetotalvalenceelectronchargeperatom.經(jīng)典自由電子論(即特魯?shù)履Ｐ?經(jīng)典自由電子論(即特魯?shù)履Ｐ?優(yōu)點：導電、導熱性；不足：無法解釋金屬晶體的結合力以及固體材料有導體、半導體和絕緣體之分金屬離子組成的勢場是非均勻的，在晶體內(nèi)隨原子重復排列而呈周期性變化。其實質是分子軌道理論在金屬晶體的應用晶體的能帶理論Energy-bandmodel2ATOMICSTRUCTUREANDBONDINGELECTRICALCONDUCTIONINMETALS其能帶理論知識見P368-370金屬共性：金屬光澤;導電導熱性；金屬加工性；導體、半導體與絕緣體之分等。nondirectionalnonsaturational.

Characteristicofmetallicbond2ATOMICSTRUCTUREANDBONDINGBondingmaybeweakorstrong;energiesrangefrom68kJ/mol(0.7eV/atom)formercury(Hg)to850kJ/mol(8.8eV/atom)fortungsten(W).Theirrespectivemeltingtemperaturesare39and3410C.Materialsaregoodconductorsofbothelectricityandheat.SecondarybondingorVanderWaalsbonding

Secondaryorphysicalforcesandenergiesarealsofoundinmanysolidmaterials;theyareweakerthantheprimaryones,butnonethelessinfluencethephysicalpropertiesofsomematerials.Secondary,vanderWaals,orphysicalbondsareweakincomparisontotheprimaryorchemicalones;bondingenergiesaretypicallyontheorderofonly10kJ/mol.Secondarybondingexistsbetweenvirtuallyallatomsormolecules,butitspresencemaybeobscuredifanyofthethreeprimarybondingtypesispresent.TheintermolecularbondingSecondarybondingisevidencedfortheinertgases,whichhavestableelectronstructures,and,inaddition,betweenmoleculesinmolecularstructuresthatarecovalentlybond.Secondarybondingforcesarisefromatomicormoleculardipoles.Inessence,anelectricdipoleexistswheneverthereissomeseparationofpositiveandnegativeportionsofanatomormolecule.Thebondingresultsfromthecoulombicattractionbetweenthepositiveendofonedipoleandthenegativeregionofanadjacentone,asindicatedinFigure2.12.Dipolemoment:偶極矩Dipoleinteractionsoccurbetweeninduceddipoles,betweeninduceddipolesandpolarmolecules(whichhavepermanentdipoles),andbetweenpolarmolecules.2ATOMICSTRUCTUREANDBONDING范德華分子鍵力色散力誘導力取向力1)VandeWaals范德華力Fluctuatinginduceddipolesbonds色散力H2

Polarmolecules-induceddipolesbonds誘導力Permanentdipolemomentsexistinsomemoleculesbyvirtueofanasymmetricalarrangementofpositivelyandnegativelychargedregions;suchmoleculesaretermedpolarmolecules.Polarmoleculescanalsoinducedipolesinadjacentnonpolarmolecules,suchasH2,andabondwillformasaresultofattractiveforcesbetweenthetwomolecules.Furthermore,themagnitudeofthisbondwillbegreaterthanforfluctuatinginduceddipoles.HCl-H2CHHHClBetweenadjacentpolarmoleculesPermanentdipolesbonds取向力

CH3Cl-CH3ClVanderWaalsforceswillalsoexistbetweenadjacentpolarmolecules.Theassociatedbondingenergiesaresignificantlygreaterthanforbondsinvolvinginduceddipoles.2)Hydrogenbonding氫鍵Thestron