18,20Oct97BondingandStructure1ChemicalBondingandMolecularStructure(Chapter9)•Ionicvs.covalentbonding•Molecularorbitalsandthecovalentbond(Ch.10)•ValenceelectronLewisdotstructuresoctetvs.non-octetresonancestructuresformalcharges•VSEPR-predictingshapesofmolecules•Bondpropertiespolarity,bondorder,bondstrength18,20Oct97BondingandStructure2ChemicalBondingProblemsandquestions—•Howisamoleculeorpolyatomicionheldtogether?•Whyareatomsdistributedatstrangeangles?•Whyaremoleculesnotflat?•Canwepredictthestructure?•Howisstructurerelatedtochemicalandphysicalproperties?18,20Oct97BondingandStructure3Mostbondsaresomewhereinbetween.FormsofChemicalBonds•Thereare2extremeformsofconnectingorbondingatoms:•Ionic—completetransferofelectronsfromoneatomtoanother•Covalent—electronssharedbetweenatoms18,20Oct97BondingandStructure4IonicIonicBondsBondsIoniccompounds-essentiallycompleteelectrontransferfromanelementoflowIE(metal)toanelementofhighelectronaffinity(EA)(nonmetal)Na(s)+1/2Cl2(g)Na++Cl-NaCl(s)-NON-DIRECTIONALbondingviaCoulomb(charge)interaction-primarilybetweenmetals(Grps1A,2Aandtransitionmetals)andnonmetals(espOandhalogens)18,20Oct97BondingandStructure5CovalentBondingCovalentbondisthesharingoftheVALENCEELECTRONSofeachatominabondRecall:Electronsaredividedbetweencoreandvalenceelectrons.ATOMcorevalenceNa1s22s22p63s1[Ne]3s1Br[Ar]3d104s24p5[Ar]3d104s24p5BrBr18,20Oct97BondingandStructure6ValenceElectrons1A1A2A2A3A3A4A4A5A5A6A6A7A7A8A8ANumberofvalenceelectronsisequaltotheGroupnumber.18,20Oct97BondingandStructure7CovalentBondingThebondarisesfromthemutualattractionof2nucleiforthesameelectrons.HB+HAHBHAAcovalentbondisabalanceofattractiveandrepulsiveforces.6_H2bond.mov18,20Oct97BondingandStructure8BondFormationAbondcanresultfroma“head-to-head”overlapofatomicorbitalsonneighboringatoms.HHCl••••••Cl••••••+OverlapofH(1s)andCl(2p)ThistypeofoverlapplacesbondingelectronsinaMOLECULARORBITALalongthelinebetweenthetwoatomsandformsaSIGMABOND().18,20Oct97BondingandStruc...
