YuwenCuiCONTENTSThreewaystoshowLewisstructureOctetRule（八隅律）SimplemoleculessuchaswaterfollowtheOctetRule,inwhicheightelectronssurroundtheoxygenatom.Thehydrogenatomssharetwoelectronseachwiththeoxygen,formingthefamiliarpicturewithtwobondsandtwolonepairs:SharedElectronsareconsideredtocontributetotheelectronrequirementsofbothatomsinvolved;thus,theelectronpairssharedbyHandOinthewatermoleculearecountedtowardboththe8-electronrequirementofoxygenand2-electronrequirementofhydrogen.DoubleBonds:4electronscontained(CarbonDioxide);TripleBonds:6electronscontained(acetylene).no,nv,andnsno——(OctetRule)TotalnumbersofElectronsneededtomakealltheatomsincovalentmoleculesreacheight-valenceelectroned(Htwo).nv——(Valence)Totalnumbersofvalenceelectronsofallatomsincovalentmolecules(ions?).ns——(Shared)Totalnumbersofsharedelectronsofallatomsincovalentmolecules.Value=no-nvBondNumber=ns/2=(no-nv)/2Example:Calculatingtheno,nv,nsandbondnumbersofthefollowingsubstances:P4S3HN3N5+H2CN2NO3-Remember:Theperiod2elementscanonlyformFOURbondsatmost!（第二周期元素最多只能形成四个键！！！！！）Fortheyhaveonlyone1sandthree2porbitalsasthevalenceorbitals.Sothestructureofnitrateionis:Becausethetypicaltheoryofvalencebondcannottellushowatomsbondincovalentmolecules,wealwaysdeterminetheirLewisstructuresbytheirnamesandthestructuresofknownsimplesubstances，（从名称和已知单质的结构来推测路易斯结构式）orbyValenceShellElectronPairRepulsionTheory.Example:hydrazoicacid,HN3,thepossibleLewisstructurescanbedrawnbelow:HowtodecidewhichoftheseLewisstructuresaremorestablethanothers?IntroducingFormalCharge(QF)（形式电荷）.Markeroftheequilibriumofthesharedelectronpairs（公用电子对公平与否的标志）.Derivation:TheLewisStructuresofN2andCO.Theyhavethesamevalueofns,6,andbondnumber=3.CalculationofFormalCharge（形式电荷的计算）DeterminationofthestabilityofLewisstructuresbyformalcharge.Formalchargemustbeassmallaspossible.Stability:0>+1,-1>+2,-2.（形式电荷尽可能小，带+2，-2形式电荷结构式可以舍去。）Tryyourbesttoavoidtheneighboratomshavethesameformalcharge.（尽可能避免相邻原子带同号电荷。）Examples：Cyanicacid,Isocyanicacida