How can bonding orbitals in diatomic oxygen be described?

1 Answer
Jan 25, 2014

The bonding orbitals in dioxygen are σ, #σ^★#, π, and #π^★# molecular orbitals (this editor will not allow me to use an asterisk symbol, so I will use a star instead).

Each O atom has the electron configuration [He] 2s² 2px² 2py 2pz.

When two O atoms approach along the z-axis, the atomic orbitals overlap to form molecular orbitals.

1s + 1s → σ(1s) and #σ^★#(1s); 2s + 2s → σ(2s) and #σ^★#(2s)
2pz + 2pz → σ(2pz) and #σ^★#(2pz)
2px + 2px → π(2px) and #π^★#(2px); 2py + 2py → π(2py) and #π^★#(2py)

The order of energies is

σ(2s) < #σ^★#(2s) < σ(2pz) < π(2px) = π(2py) < #π^★#(2px) = #π^★#(2py) < #σ^★#(2pz).

In the following diagram, the atomic orbitals of the O atoms are on either side, and the molecular orbitals of the O₂ molecule are in the middle.

image.wistatutor.com

We place the valence electrons in the atomic orbitals and the molecular orbitals and get the diagram below.

image.wistatutor.com

We write the electron configuration of O₂ as
σ(1s)² #σ^★#(1s)² σ(2s)² #σ^★#(2s)² σ(2pz)² π(2px)² π(2py)² #π^★#(2px) #π^★#(2py).