chapter 8 molecular shape：8章分子形状

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1、Chapter8MolecularShapeObjectives8-1TheShapeofSmallMolecules·DescribetheVSEPRtheory·Identifythecommonshapesofsmallmolecules8-2Polarity·Explainwhatdeterminesthepolarityofamolecule·Explainwhywaterisapolarmolecule118-1TheShapeofSmallMoleculesWhataresomehouseholduses

2、forwater?Whatissomewaythatwaterhasbeenamemorablepartofanexperienceinyourlife?Whatpropertiesofwatermadethispossible?MolecularGeometry·Howbondsarearrangedinamoleculedeterminestheshapeofamolecule·Structuralformuladoesnotindicateshapeofamolecule.DrawLewisdotstructur

3、eforammonia,NH3ØStructuralformuladoesnotshowhowbondsarearrangedinspace(3D)·Ball&Stickmodels-areusedtoindicatemolecularshape.Ballsarenuclei&sticksarebonds.Seefigures8.4,8.5&8.7·Therearemanyshapesofsmallmoleculesbutallaresymmetrical-meaningthebondsandatomsarearran

4、gedinaregularpatternwithequaldistancesseparatingtheatomsthatarenotbondedtogether.WHY?ØValenceshellelectronsrepeleachotherbecauseofsimilarelectricalcharge11·VSEPR(valenceshellelectronpairrepulsion)Theory-inasmallmolecule,thepairsofvalenceelectronsarearrangedasfar

5、apartfromeachotheraspossible.ØThisisduetotherepulsionoflikechargesone-ØEachpairofvalenceelectronswearetalkingaboutisachemicalbondØTherearesomeexceptionswithtransitionmetalsbutthisisgenerallytrueØThismakesthemolecularshapeofsmallmoleculespredictable·5mostcommonsh

6、apes1)Lineara.Moleculesw/2atoms,IE>O2,HClb.Manymoleculesw/3atoms,IE>CO2c.Bondangle-geometricanglebetween2adjacentbonds.ForCO2(linearshape)bondangleis180°,sothatthevalenceelectronscanbeasfarapartfromeachotheraspossible.BuildCO22)TrigonalPlanar-4atomsa.Meaningtria

7、ngular&flatb.BCl3orborontrichloride-i.the3Clatomsarearrangedintheshapeofanequilateraltriangle(allsidesareequal)ii.boronisinthecenterandhasnounsharedelectronpairs(3valencee-).Thisistypicaloftrigonalplanarshapedmolecules.iii.bondangleis120°11BuildBCl31)Tetrahedal-

8、5atomsa.Tetrahedal=foursurfacesb.=methane,animportantfuel&principlecomponentofnaturalgasc.Bondangle=109.5°ifonly2dimensionalgreatestanglewouldbe90°BuildCH4Configurati