The energy of σ2pz molecular orbital is greater

The general sequence of the energy level of the molecular orbital is

σ1s < σ*1s < σ2s< σ*2s < π2px = π2py < σ2pz

N2 σ1s2 σ*1s2 σ2s2 σ*2s2 π2p2x = π2p2y σ2p2z

N2+ σ1s2 σ*1s2 σ2s2 σ*2s2 π2p2x = π2p2y σ2p1z

N2- σ1s2 σ*1s2 σ2s2 σ*2s2 π2p2x = π2p2y σ2p2z σ2p2x

N22+ σ1s2 σ*1s2 σ2s2 σ*2s2 π2p2x = π2p2y

Bond order = ½[electrons in BMO – electrons in ABMO]

For N2 = 10-4/2 = 3

Bond order for N2+= 9-4/2 = 2.5

Bond order for N2-= 10-5/2 = 2.5

Bond order for N22+= 8-4/2 = 2

Thus, the order of stability is:

N2> N2- > N2+> N22+