同核双原子分子的电子结构A

3.Thestructureofhomonucleardiatomicmoleculesa.Theground-stateelectronicconfigurationsTheaufbau(building-up)principleinmolecules:PauliexclusionprincipleTheminimumenergyprincipleHund’srule.HEnergyHH21s1s1g1*uDiatomicmolecules:ThebondinginH2Electronicconfiguration:H2

1

g2H2+1

g1b(H2+)

=0.5;b(H2)=1;H+H

H2

E=

432kJ/mol.n:Electronsinbondingorbitalsn*:ElectronsinantibondingorbitalsDiatomicmolecules:ThebondinginHe2HeEnergyHeHe21s1s1g1*uThebondorder(BO)ofHe2:b=(2-2)/2=0

He2doesnotexist

asacovalentlyboundedmolecule!He2+:b=(2-1)/2=0.5,exists!(1

g21

u*1)Diatomicmolecules:HomonuclearMoleculesoftheSecondPeriodb(Li2)=(4-2)/2=1Li2couldexist.Li2

Li+Li

E=105kJ/molLi2:(1

g)2(1

u*)2(2

g)2LiEnergyLiLi21s1s1g1*u2s2s2g2*uBeEnergyBeBe21s1s1g1*u2s2s2g2*uDiatomicmolecules:HomonuclearMoleculesoftheSecondPeriodb(Be2)=(4-4)/2=0Be2couldnotexist!ThisproducesanantibondingMOof*usymmetry.Diatomicmolecules:ThebondinginF22pzA+2pzBThebinationsof

symmetry:ThisproducesabondingMOof

gsymmetry.2pzA-2pzB3g-3*u+ThisproducesabondingMOof

usymmetry.Diatomicmolecules:ThebondinginF22pyA+2pyBThefirstsetofbinationsofsymmetry:1uThisproducesanantibondingMOof*gsymmetry.-2pyA2pyB1*gSimilarly,thebinationoftwo2pxAOsofthetwoatomsresultsinabonding

uMOandanantibondingg*MO.Diatomicmolecules:ThebondinginF22pyA+2pyB

2pMOvs2pMO.1u2pzA-2pzB3g-As

<

<0

E

<E

E

>E

,E*<E*2pA2pB2pAFEnergyFF22s2s1g1*u2p2p2g2*u1u1*g(px,py)pzO2:KK(

2s)2(

*2s)2(

2p)2(

2p)4(

*2p)2

orKK(1

g)2(1

*u)2(2

g)2(1

u)4(1

*g)2

F2:KK(

2s)2(

*2s)2(

2p)2(

2p)4(

*2p)4

orKK(