材料科学导论第二章原子键

材料科学导论

IntroductiontoMaterialsScienceDepartmentofEnvironmentalandChemicalEngineering,NanchangHangkonguniversityFumaoshengChapter2/AtomicstructureandinteratomicbondingLearningobjectives：Whycantheatomsbondtogetherandcompriseasolid?Howmanybondingtypesarethereinmaterials？Whatarethecloseinterrelationshipsbetweenpropertiesofmaterialsandtheirbondingtypes本章基本要求教学目的：从原子结构、结合键的不同层次去认识材料本质,加深对材料结构与成分与性能之间的关系的理解。主要内容：了解原子结构对原子间结合键和材料性能的影响,掌握原子间的结合键种类及其各自特点,以及它们对材料性能的影响。重点与难点：

重点：原子间的结合键种类及其各自特点。

难点：原子间的结合键对材料性能的影响教学方法与手段授课方式：讲课、讲座、课堂讨论、自学

教学手段：多媒体授课课时安排：2主要讲述内容2.1、Atomicstructure原子结构2.2、Interatomicbonding原子间结合键

材料的结构键合结构晶体结构组织结构原子间的结合键结构原子或分子排列结构宏观组织和显微组织结构原子结构原子中的电子结构晶体：原子排列长程有序，有周期

晶体结构非晶体：原子排列短程有序，无周期准晶体：原子排列长程有序，无周期定义：组成材料的不同物质表示出的某种形态特征组织结构匀晶型组织共晶型组织包晶型组织相图特征结构特征马氏体组织奥氏体组织贝氏体组织…...组合特征单相组织两相组织多相组织…...结构分析2ATOMICSTRUCTUREANDBONDINGGold:FCC用扫描遂道显微镜观察原子的排列情况扫描隧道显微镜像在扫描隧道显微镜下，在硅（111）表面直接取出原子而“刻写”出平均线宽为2纳米的字体。2.1AtomicStructure

ATOMICSTRUCTUREANDINTERATOMIC

BONDING2决定着材料绝大部分性能的最小因素原子结构1）Bohratomicclassicalmodel玻尔模型

ATOMICSTRUCTUREANDINTERATOMIC

BONDING2优点：能定性地解释原子的稳定性即定态规则（定态的存在）和线状原子光谱缺点：它不能解释电子衍射现象,因为它仍然是将电子视为服从牛顿力学的经典粒子。

1.Electronorbitals2.Quantizedenergy2ATOMICSTRUCTUREANDBONDING2）Wave-Mechanicsmodel波动力学模型电子和一切微观粒子都具有二象性，即既具有粒子性(particle-like)

，又具有波动性(wavelike)。

ATOMICSTRUCTUREANDINTERATOMIC

BONDING22、Wave-Mechanicsmodel波动性:电子某一瞬时在某一位置的几率(即可能性Probability)图2.3玻尔模型和波动力学模型比较

ATOMICSTRUCTUREANDINTERATOMIC

BONDING2科学的描述体系物理模型（物理参数）量子数每一个电子的能级可由四个量子数确定

ATOMICSTRUCTUREANDINTERATOMIC

BONDING2薛定谔方程schrodingerequation方程中引入波函数的概念，以取代经典物理中的圆形的固定轨道，解得的波函数（习惯上又称原子轨道）描绘了电子在核外空间各处的位置出现的几率，相当于给出了电子运动的“轨道”。Atomicstructure——electronarrangementFourquantumnumbers

ATOMICSTRUCTUREANDINTERATOMIC

BONDING2主量子数(Principalquantumnumber)n表示电子所处的量子壳层shell，为正整数1，2，3，。。。n值是确定电子离核远近和能级的主要参数1角量子数l

(azimuthalquantumnumber)l值基本反映原子轨道的形状l=0,1,2,…,n-1.n为主量子数。例如：n=2,l=0,1角量子数往往用字母表示，l=0s能级l=1p能级l=2d能级l=3f能级2自旋量子数ms

(spinquantumnumber)表示电子的自旋方向，ms=+1/2,-1/24磁量子数mL

(magneticquantumnumber)m值基本反映原子轨道的空间取向.磁量子数mL给出每个角量子数的能级数（轨道数），为-l,+l之间的整数例如：l=2,则mL=-2，-1，0，1，2，（共2l+1个）32ATOMICSTRUCTUREANDBONDINGElectronconfiguration核外电子组态Todeterminethemannerinwhichelectronsstatesarefilledwithelectronsoutsideofnucleus,threeprinciplesarefollowedthelowestpossibleenergylawPauliExclusionPrincipleHundlaw

ATOMICSTRUCTUREANDINTERATOMIC

BONDING22ATOMICSTRUCTUREANDBONDING2ATOMICSTRUCTUREANDBONDINGElectronconfigurationforsodiumNa1s22s22p63s1theperiodicstableofelements2ATOMICSTRUCTUREANDBONDING2.2、Interatomicbonding

原子间结合键Thenetforcebetweenapairofoppositelychargedionsisequaltothesumoftheattractiveandrepulsiveforces.

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

r0ora0:平衡距离2ATOMICSTRUCTUREANDBONDING

r0ora0:平衡距离TheirmagnitudeofFN,FA,FRvarywiththedistance2ATOMICSTRUCTUREANDBONDING2.2.2interatomicbondtypesClassificationofinteratomicbondsPrimaryinteratomicbonds主原子结合键SecondarybondingorVanderWaalsbonding次原子间结合键原子结构金属键共价键离子键范德华键原子原子键聚集体

ATOMICSTRUCTUREANDINTERATOMIC

BONDINGprimaryatomicbonds离子键1.IONICBONDING离子键价电子的完全贡献或获得2ATOMICSTRUCTUREANDBONDINGFormationofasodiumchlorideionpairfromsodiumandchlorineatoms.Intheionizationprocessa3s1electronfromthesodiumatomistransferredtoahalf-empty3porbitalofthechlorineatom.原子间距及结合能Coulombicbondingforce:静电库仑力

Ionicbondingistermednondirectional,thatis,themagnitudeofthebondisequalinalldirectionsaroundanion.Itfollowsthatforionicmaterialstobestable,allpositiveionsmusthaveasnearestneighborsnegativelychargedionsinathree-dimensionalscheme,andviceversa.Thepredominantbondinginceramicmaterialsisionic.Incovalentbondingstableelectronconfigurationsareassumedbythesharingofelectronsbetweenadjacentatoms.Twoatomsthatarecovalentlybondedwilleachcontributeatleastoneelectrontothebond,andthesharedelectronsmaybeconsideredtobelongtobothatoms.CovalentbondingisschematicallyillustratedinFigure2.10foramoleculeofmethane(CH4).2.COVALNETBONDING共价键2ATOMICSTRUCTUREANDBONDING价键理论共价键数个原子共享部分电子，有方向性分子轨道理论2ATOMICSTRUCTUREANDBONDING2s22p5(share1p)2s22p4(share2p)2s22p3(share3p)DirectionalSaturational.

Characteristicofcovalentbond2ATOMICSTRUCTUREANDBONDING

Covalentbond

maybeverystrong,asindiamond;ortheymaybeveryweak,aswithbismuth.Materialsareelectricallyandthermallyinsulative,becauseofnoneproductionofelectronsmovingeasily.人们对金属晶体中的电子状态的认识经历了一个从经典自由电子论(即特鲁德模型)到现代能带理论的发展过程3.METALLICBONDING2ATOMICSTRUCTUREANDBONDING经典自由电子论(即特鲁德模型)Metallicbonding,thefinalprimarybondingtype,isfoundinmetalsandtheiralloys.Arelativelysimplemodelhasbeenproposedthatverynearlyapproximatesthebondingscheme.Metallicmaterialshaveone,two,oratmost,threevalenceelectrons.Withthismodel,thesevalenceelectronsarenotboundtoanyparticularatominthesolidandaremoreorlessfreetodriftthroughouttheentiremetal.Theymaybethoughtofasbelongingtothemetalasawhole,orforminga‘‘seaofelectrons’’oran‘‘electroncloud.’’Theremainingnonvalenceelectronsandatomicnucleiformwhatarecalledioncores,whichpossessanetpositivechargeequalinmagnitudetothetotalvalenceelectronchargeperatom.经典自由电子论(即特鲁德模型)经典自由电子论(即特鲁德模型)优点：导电、导热性；不足：无法解释金属晶体的结合力以及固体材料有导体、半导体和绝缘体之分金属离子组成的势场是非均匀的，在晶体内随原子重复排列而呈周期性变化。其实质是分子轨道理论在金属晶体的应用晶体的能带理论Energy-bandmodel2ATOMICSTRUCTUREANDBONDINGELECTRICALCONDUCTIONINMETALS其能带理论知识见P368-370金属共性：金属光泽;导电导热性；金属加工性；导体、半导体与绝缘体之分等。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:偶极矩Dipoleinteractionsoccurbetweeninduceddipoles,betweeninduceddipolesandpolarmolecules(whichhavepermanentdipoles),andbetweenpolarmolecules.2ATOMICSTRUCTUREANDBONDING范德华分子键力色散力诱导力取向力1)VandeWaals范德华力Fluctuatinginduceddipolesbonds色散力H2

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

CH3Cl-CH3ClVanderWaalsforceswillalsoexistbetweenadjacentpolarmolecules.Theassociatedbondingenergiesaresignificantlygreaterthanforbondsinvolvinginduceddipoles.2)Hydrogenbonding氢键Thestron