The energy of σ2pz molecular orbital is greater

Question:

The energy of σ2pz molecular orbital is greater than π2px and π2py molecular orbitals in nitrogen molecule. Write the complete sequence of energy levels in the increasing order of energy in the molecule. Compare the relative stability and the magnetic behaviour of the following species :

N2, N2+ , N2- , N22+

Solution:

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+

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