chemicalBonding化學鍵解析課件

ChemicalBondingChemicalbond:attractiveforceholdingtwoormoreatomstogether.Covalentbondresultsfromsharingelectronsbetweentheatoms.Usuallyfoundbetweennonmetals.Ionicbondresultsfromthetransferofelectronsfromametaltoanonmetal.Metallicbond:attractiveforceholdingpuremetalstogether.ChemicalBonds,LewisSymbols,andtheOctetRuleFigure8.3:IonicBondingFigure8.5:CovalentBondingChemicalBondsBondTypeSingleDoubleTriple#ofe’s246Notation

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Bondorder123BondstrengthIncreasesfromSingletoTripleBondlengthDecreasesfromSingletoTripleStrengthsofCovalentBondsLewisSymbolsChemicalBonds,LewisSymbols,andtheOctetRuleTheOctetRuleAllnoblegasesexceptHehasans2p6configuration.Octetrule:atomstendtogain,lose,orshareelectronsuntiltheyaresurroundedby8valenceelectrons(4electronpairs).Caution:therearemanyexceptionstotheoctetrule.ChemicalBonds,LewisSymbols,andtheOctetRuleBondPolarityandElectronegativityElectronegativityElectronegativity:Theabilityofoneatomsinamoleculetoattractelectronstoitself.Paulingsetelectronegativitiesonascalefrom0.7(Cs)to4.0(F).Electronegativityincreasesacrossaperiodanddownagroup.Figure8.6:ElectronegativitiesofElementsElectronegativityBondPolarityandElectronegativityFigure8.7:ElectronegativityandBondPolarityThereisnosharpdistinctionbetweenbondingtypes.Thepositiveend(orpole)inapolarbondisrepresented+andthenegativepole-.HyperChemDrawingLewisStructuresFollowStepbyStepMethod(SeeNgWeb-site)Totalallvalenceelectrons.[ConsiderCharge]Writesymbolsfortheatomsandguessskeletonstructure[defineacentralatom].Placeapairofelectronsineachbond.Completeoctetsofsurroundingatoms.[H=2only]Placeleftoverelectronsinpairsonthecentralatom.Iftherearenotenoughelectronstogivethecentralatomanoctet,lookformultiplebondsbytransferringelectronsuntileachatomhaseightelectronsaroundit.HyperChemCyberChem(Lewis)videoLewisStructures–Examples-ILewisStructures–Examples-IILewisStructures–Examples-IIILewisStructures–Examples-IVExceptionstotheOctetRuleCentralAtomsHavingLessthananOctetRelativelyrare.MoleculeswithlessthananoctetaretypicalforcompoundsofGroups1A,2A,and3A.MosttypicalexampleisBF3.FormalchargesindicatethattheLewisstructurewithanincompleteoctetismoreimportantthantheoneswithdoublebonds.Exceptions–CentralAtoms-LessthananOctetExceptionstotheOctetRuleCentralAtomsHavingMorethananOctetThisisthelargestclassofexceptions.Atomsfromthe3rdperiodonwardscanaccommodatemorethananoctet.Beyondthethirdperiod,thed-orbitalsarelowenoughinenergytoparticipateinbondingandaccepttheextraelectrondensity.HyperChemExceptions–CentralAtoms-GreaterthananOctetTherearefivefundamentalgeometriesformolecularshape:MolecularShapes:VSEPRMolecularShapes–3DNotationsVSEPR(Ballons)-MovieClipFigure9.3HyperChemSummaryofVSEPRMolecularShapese-pairsNotationNameofVSEPRshapeExamples2AX2LinearHgCl2,ZnI2,CS2,CO23AX3TrigonalplanarBF3,GaI3AX2ENon-linear(Bent)SO2,SnCl24AX4TetrahedralCCl4,CH4,BF4-AX3E(Trigonal)PyramidalNH3,OH3-AX2E2Non-Linear(Bent)H2O,SeCl25AX5TrigonalbipyramidalPCl5,PF5AX4EDistortedtetrahedral(see-sawed)TeCl4,SF4AX3E2T-ShapedClF3,BrF3AX2E3LinearI3-,ICl2-

6AX6OctahedralSF6,PF6-AX5ESquarePyramidalIF5,BrF5AX4E2SquarePlanarICl4-,BrF4-SeeNgWeb-siteHyperChemCyberChmGemsExamples:VSEPRMolecularShapes-IExamples:VSEPRMolecularShapes–I–F08Examples:VSEPRMolecularShapes-IIExamples:VSEPRMolecularShapes–II–F08Examples:VSEPRMolecularShapes-IIIExamples:VSEPRMolecularShapes–III–F08HyperChemExamples:VSEPRMolecularShapes-IVExamples:VSEPRMolecularShapes-IV TheEffectofNonbondingElectronsByexperiment,theH-X-HbondangledecreasesonmovingfromCtoNtoO:Sinceelectronsinabondareattractedbytwonuclei,theydonotrepelasmuchaslonepairs.Therefore,thebondangledecreasesasthenumberoflonepairsincreasesVSEPRModelHyperChemFigure9.10:ShapesofLargerMoleculesInaceticacid,CH3COOH,therearethreecentralatoms.VSEPRModelHyperChemShapesofLargerMoleculesInglycine(simplestaminoacid),NH2CH2CO2H,therearefourpossiblecentralatoms.DrawtheLewisStructureandthe3DVSEPRMolecularGeometryforglycine.Indicatethenameoftheshapeforallpossiblecentralatoms,includingestimationofbondangles.Hint1:Designatethe2ndcarbonintheformulaasthecentralatominskeletonstructure.Hint2:Theacidportionofglycineisthesameasthatofaceticacid.Lewis-VSEPRHWfor10/30/09.Due11/2/09.HyperChemFigure8.10:DrawingLewisStructuresResonanceStructuresFigure9.12HyperChemFigure9.11:MolecularShapeandMolecularPolarityHyperChemFigure9.13:MolecularShapeandMolecularPolarityHyperChemLewisstructuresandVSEPRdonotexplainwhyabondforms.Howdoweaccountforshapeintermsofquantummechanics?Whataretheorbitalsthatareinvolvedinbonding?WeuseValenceBondTheory:Bondsformwhenorbitalsonatomsoverlap.Therearetwoelectronsofoppositespinintheorbitaloverlap.CovalentBondingandOrbitalOverlapGems-MovieClipFigure9.14:CovalentBondingandOrbitalOverlapTodeterminetheelectronpairgeometry:drawtheLewisstructure,countthetotalnumberofelectronpairsaroundthecentralatom,arrangetheelectronpairsinoneoftheabovegeometriestominimizee--e-repulsion,andcountmult