Question

Explain the formation of O2 molecule by molecular orbital theory.

Answer 1

number of electrons in O₂ molecule = 16 .
Now, we have to write molecular configuration ,
σ1s², σ*1s² , σ2s² , σ*2s² , σ2Pz² , π2Px² ≈ π2Py² , π*2Px¹ ≈ π*2Py¹
antibonding molecular orbitals = σ*1s², σ*2s² , π*2Px¹ ≈ π*2Py¹
number of antibonding electrons = 2 + 2 + 1 + 1 = 6
bonding molecular orbitals = σ1s² , σ2s², σ2Pz² , π2Px² ≈ π2Py²
Number of bonding electrons = 2 + 2 + 2 + 2 + 2 = 10

Now, bond order = 1/2 [bonding electrons - antibonding electrons ]
= 1/2 [ 10 - 6 ] = 2
Hence, bond order of O₂ molecule = 2
also you can see in configuration , two antibonding molecular orbitals are incomplete ( π*2Px¹ ≈ π*2Pz¹) . Hence, molecule is diamagnetic in nature.