covalent-bonding-AP化学

CovalentbondingCovalentmoleculesThesimplestmoleculeisH2:Thepairofsharedelectronsconstitutesacovalentbond.Bondtypes•Ionicbondpolarbond•Covalentbondnon-polarbondHowtoidentifythebondtypes?LocalizedElectronModelPolarity(Polarbondandnon-polarbond)•Inanonpolarbond,thebondingelectronsaresharedequally:H2,Cl2:•Inapolarbond,electronsaresharedunequallybecauseofthedifferenceinelectronegativityPolarityreferstoaseparationofpositiveandnegativecharge.HCl:DipoleMomentμ=q·rLocalizedElectronModelElectronegativityLocalizedElectronModelBondPolarityApolarbondcanbepicturedusingpartialcharges:=0.9ElectronegativityDifferenceBondType0-0.5Nonpolar0.5-1.7Polar1.7Ionic2.13.0+HClLocalizedElectronModelBondPolarityLewisstructureModelsforCovalentBondingLocalizedelectronmodel(Valencebondmodel)VSEPRmodelHybridizationMolecularorbitalmodelLocalizedElectronModel•Simplemodel,easilyapplied.•Amoleculeiscomposedofatomsthatareboundtogetherbysharingpairsofelectronsusingtheatomicorbitalsoftheboundatoms.•ThreeParts1)ValenceelectronsusingLewisstructures2)PredictionofgeometryusingVSEPR3)DescriptionofthetypesoforbitalsLocalizedElectronModelLewisStructureHH+ClClH2:orHHCl2:ClCl+orClClHHBondingelectronsNonbondingelectrons•Showshowthevalenceelectronsarearranged.•Onedotforeachvalenceelectron.•Astablecompoundhasallitsatomswithanoblegasconfiguration.•Hydrogenfollowstheduetrule.•Therestfollowtheoctetrule.•Bondingpairistheonebetweenthesymbols.LocalizedElectronModelLewisStructureRules•Sumthevalenceelectrons(A).•Useapairofelectronstoformabondbetweeneachpairofbondatom•Arrangetheremainingelectronstosatisfytheduetruleforhydrogenandtheoctetruleforthesecond-twoelementsDrawLewisstructuresfor:H2OPCl3CO2NO+LocalizedElectronModelLewisStructureExceptionstotheoctet•BF3BeCl2Beandgroup3elementsoftendonotachieveoctet•Havelessthanandoctet,forelectrondeficientmolecules.•SF6PCl5•Thirdrowandlargerelementscanexceedtheoctet•Use3dorbitals?EXERCISE:•TrytodrawLewisstructureofI3-NO3-Why?LocalizedElectronModelLewisStructureExceptionstotheoctetLocalizedElectronModelLewisStructureResonance•Sometimesthereismorethanonevalidstructureforanmoleculeorion.•NO3-•Usedoublearrowstoindicateitisthe“average”ofthestructures.•Itdoesn’tswitchbetweenthem.TheactualstructureisanaverageofthereasonacestructuresallthreebondswillbethesamelengthbecausenoparticularreasonaceformispreferredovertheothersLocalizedElectronModelLewisStructureFormalChargeThedifferencebetweenthenumberofvalenceelectronsonthefreeatomandthatassignedinthemolecule.•Wecounthalftheelectronsineachbondas“belonging”totheatom.•Moleculestrytoachieveaslowaformalchargeaspossible.•Negativeformalchargesshouldbeonelectronegativeelements.PO43-LocalizedElectronModelLewisStructureResonanceLocalizedElectronModelMoleculargeometryVSEPRModelCH4NH3ValanceshellelectronpairrepulsionCO2linearTrigonalplanartetrahedralpyramidalLocalizedElectronModelMoleculargeometryVSEPRModelT-ShapeSquarepyramidOctahedralVshapeH2OEXERCISEPredicttheshapeforCF4,NF3,andBeI2.•DrawtheLewisStructure•Counttheelectronpairsanddeterminethearrangementthatwillminimizerepulsions•DeterminethepositionsoftheatomsandnamethestructureLocalizedElectronModelMoleculargeometryVSEPRModelComplexstructureOrbitalsandCovalentBondLewisstructureModelsforChemicalBondingLocalizedelectronmodel(Valencebondmodel)VSEPRmodelHybridizationMolecularorbitalmodelAtomicOrbitalsDon’tWork•toexplainmoleculargeometry.•Inmethane,CH4,theshapeistetrahedral.•Thevalenceelectronsofcarbonshouldbetwoins,andtwoinp.•theporbitalswouldhavetobeatrightangles.•TheatomicorbitalschangewhenmakingamoleculeTwotypesofBonds•Sigmabondsfromoverlapoforbitals.Betweentheatoms.•Pibond(pbond)aboveandbelowatomsbetweenadjacentporbitals.•Thetwobondsofadoublebond.Sigmabondingorbitals•Fromsorbitalsonseparateatoms++sorbitalsorbital++++SigmabondingmolecularorbitalSigmabondingorbitals•FromporbitalsonseparateatomsporbitalporbitalSigmabondingmolecularorbitalPibondingorbitals•porbitalsonseparateatomsPibondingmolecularorbitalsp3hybridizationsp3hybridizationsp3hybridizationEnergy2p2sHybridizationsp3sp3hybridizationIntermsofenergysp2hybridization•Perpendicular•Theoverlapoforbitalsmakesasigmabond(sbond)sp2hybridizationsp2hybridizationethynesphybridizationsphybridizationSigmaandpibonds•Allsinglebondsaresigmabonds•Adoublebondisonesigmaandonepibond•Atriplebondisonesigmaandtwopibonds.describethebondinginCO2•Ccanmaketwosandtwop•OcanmakeonesandonepCOOdescribethebondinginN2•PF5•Themodelpredictsthatwemustusethedorbitals.•dsp3hybridization•Thereissomecontroversyabouthowinvolvedthedorbitalsare.dsp3hybridizationBreakingtheoctetdsp3hybridization•Trigonalbipyrimidal•canonlysbond.•can’tpbond.•basicshapeforfivethings.PCl5Can’ttellthehybridizationofClAssumesp3tominimizerepulsionofelectronpairs.dsp3hybridization•getsustosixthingsaround•Octahedral•Onlyσbondd2sp3hybridizationpdelocalizedbonding•C6H6HHHHHHHHHHHHC6H6NO3-LocalizedElectronModelBondstrengthIndexesofbondstrength•Bondlength•Bondenergy•Bondorder:refertotheaveragenumberofbon