chemical-bonding--basic-concepts

Chapter8ChemicalBondingI:BasicConceptsCopyrightMcGraw-Hill20091CopyrightMcGraw-Hill20092CopyrightMcGraw-Hill20098.1LewisDotSymbols•Valenceelectronsdetermineanelement’schemistry.•Lewisdotsymbolsrepresentthevalenceelectronsofanatomasdotsarrangedaroundtheatomicsymbol.•Mostusefulformain-groupelementsCopyrightMcGraw-Hill20093CopyrightMcGraw-Hill2009LewisDotSymbolsoftheMainGroupElementsCopyrightMcGraw-Hill20094CopyrightMcGraw-Hill2009WriteLewisdotsymbolsforthefollowing:(a)N(b)S2(c)K+CopyrightMcGraw-Hill20095CopyrightMcGraw-Hill2009WriteLewisdotsymbolsforthefollowing:(a)N(b)S2(c)K+K+N•••••••••S••••2CopyrightMcGraw-Hill20096CopyrightMcGraw-Hill20098.2IonicBondingNa•Cl•••••••+Na+Cl••••••••+IE1+EA1=496kJ/mol349kJ/mol=147kJ/molfH=–410.9kJ/molm.p.=801oC•Ionicbond:electrostaticforcethatholdsoppositelychargeparticlestogether•Formedbetweencationsandanions•ExampleCopyrightMcGraw-Hill20097MicroscopicViewofNaClFormationCopyrightMcGraw-Hill20098CopyrightMcGraw-Hill2009NaCl(s)Na+(g)+Cl(g)Hlattice=+788kJ/molBecausetheyaredefinedasanamountofenergy,latticeenergiesarealwayspositive.+--------+++++++•Latticeenergy=theenergyrequiredtocompletelyseparateonemoleofasolidioniccompoundintogaseousionsCopyrightMcGraw-Hill20099CopyrightMcGraw-Hill2009Q=amountofcharged=distanceofseparationdQ1Q2•Coulombicattraction:221dQQF•Latticeenergy(likeacoulombicforce)dependson•Magnitudeofcharges•DistancebetweenthechargesCopyrightMcGraw-Hill200910LatticeenergiesofalkalimetaliodidesCopyrightMcGraw-Hill200911CopyrightMcGraw-Hill2009TheionicradiisumsforLiFandMgOare2.01and2.06Å,respectively,yettheirlatticeenergiesare1030and3795kJ/mol.WhyisthelatticeenergyofMgOnearlyfourtimesthatofLiF?CopyrightMcGraw-Hill200912CopyrightMcGraw-Hill2009•Born-Habercycle:AmethodtodeterminelatticeenergiesCopyrightMcGraw-Hill200913CopyrightMcGraw-Hill2009•Born-HabercycleforCaOCa(s)+(1/2)O2(g)CaO(s)Ca(g)#1#1Heatofsublimation=Hf[Ca(g)]=+178kJ/molCa2+(g)#2#21st&2ndionizationenergies=I1(Ca)+I2(Ca)=+1734.5kJ/molO(g)#3#3(1/2)Bondenthalpy=(1/2)D(O=O)=Hf[O(g)]=+247.5kJ/molO2(g)#4#41st&2ndelectronaffinities=EA1(O)+EA2(O)=+603kJ/mol+#5#5(LatticeEnergy)=Hlattice[CaO(s)]=(theunknown)#6#6Standardenthalpyofformation=Hf[CaO(s)]=635kJ/mol+178+1734.5+247.5+603Hlatt=635Hlattice=+3398kJ/molCopyrightMcGraw-Hill200914CopyrightMcGraw-Hill20098.3CovalentBonding•Atomsshareelectronstoformcovalentbonds.•Informingthebondtheatomsachieveamorestableelectronconfiguration.•HH•+••HHH–HorCopyrightMcGraw-Hill200915CopyrightMcGraw-Hill2009•Octet:Eightisa“magic”numberofelectrons.•OctetRule:Atomswillgain,lose,orshareelectronstoacquireeightvalenceelectronsNa•Cl•••••••+Na+Cl••••••••+Examples:H••O•••••H•O••••••••HH++CopyrightMcGraw-Hill200916CopyrightMcGraw-Hill2009•LewisStructures•HH•+••HHH–HCl•••••••+Cl•••••••Cl••••••••Cl••••••Cl••••••Cl••••••–SharedelectronsBondsNon-bondingvalenceelectronsLonepairsCopyrightMcGraw-Hill200917CopyrightMcGraw-Hill2009•MultipleBonds-Thenumberofsharedelectronpairsisthenumberofbonds.Cl••••••••Cl••••••Cl••••••Cl••••••–SingleBondO••••C••••••••O••••O••••O••••=C=DoubleBond••••N••••••NN••••NTripleBondCopyrightMcGraw-Hill200918CopyrightMcGraw-Hill2009•BondstrengthandbondlengthbondstrengthsingledoubletriplebondlengthsingledoubletripleN–NN=NNNBondStrength163kJ/mol418kJ/mol941kJ/molBondLength1.47Å1.24Å1.10ÅCopyrightMcGraw-Hill2009198.4ElectronegativityandPolarity•Nonpolarcovalentbond=electronsaresharedequallybytwobondedatoms•Polarcovalentbond=electronsaresharedunequallybytwobondedatomsCopyrightMcGraw-Hill200920redhighelectrondensitygreenintermediateelectrondensitybluelowelectrondensity•Electrondensitydistributions+-H–FalternaterepresentationsH–FCopyrightMcGraw-Hill200921CopyrightMcGraw-Hill2009•Electronegativity:abilityofanatomtodrawsharedelectronstoitself.-Moreelectronegativeelementsattractelectronsmorestrongly.•relativescale•relatedtoIEandEA•unitless•smallestelectronegativity:Cs0.7•largestelectronegativity:F4.0CopyrightMcGraw-Hill200922CopyrightMcGraw-Hill2009Electronegativity:ThePaulingScaleCopyrightMcGraw-Hill200923CopyrightMcGraw-Hill2009VariationinElectronegativitywithAtomicNumberCopyrightMcGraw-Hill200924CopyrightMcGraw-Hill2009•Polarandnonpolarbonds2.1-2.1=0.04.0-2.1=1.94.0-0.9=3.1nonpolarcovalentpolarcovalentionic2.0isionicCopyrightMcGraw-Hill200925CopyrightMcGraw-Hill2009•Dipolemomentsandpartialcharges-Polarbondsoftenresultinpolarmolecules.-Apolarmoleculepossessesadipole.-dipolemoment()=thequantitativemeasureofadipole=Qrr+Q–Q+-H–FSIunit:coulomb•meter(C•m)commonunit:debye(D)1D=3.341030C•mHF1.82DHCl1.08DHBr0.82DHI0.44DCopyrightMcGraw-Hill200926CopyrightMcGraw-Hill20098.5DrawingLewisStructures1)Drawskeletalstructurewiththecentralatombeingtheleastelectronegativeelement.2)Sumthevalenceelectrons.Add1electronforeachnegativechargeandsubtract1electronforeachpositivecharge.3)Subtract2electronsforeachbondintheskeletalstructure.4)Completeelectronoctetsforatomsbondedtothecentralatomexceptforhydrogen.5)Placeextraelectronsonthecentralatom.6)Addmultipleb