MO Diagram for $N_{2}$ (Z ≤ 7, with s-p mixing)

The MO energy order for homonuclear diatomics with Z ≤ 7:

$\sigma_{1s} < \sigma^*_{1s} < \sigma_{2s} < \sigma^*_{2s} < \pi_{2p_x} = \pi_{2p_y} < \sigma_{2p} < \pi^*_{2p_x} = \pi^*_{2p_y} < \sigma^*_{2p}$

$N_{2}$ electron configuration (14e): $(\sigma_{1s})^2 (\sigma^*_{1s})^2 (\sigma_{2s})^2 (\sigma^*_{2s})^2 (\pi_{2p})^4 (\sigma_{2p})^2$

• Bonding electrons: σ1s(2) + σ2s(2) + π2p(4) + σ2p(2) = 10
• Antibonding electrons: σ1s(2) + σ2s(2) = 4
• BO = (10−4)/2 = 3; Diamagnetic

MO Diagram for $O_{2}$ (Z > 7, no mixing)

$\sigma_{1s} < \sigma^*_{1s} < \sigma_{2s} < \sigma^*_{2s} < \sigma_{2p} < \pi_{2p_x} = \pi_{2p_y} < \pi^*_{2p_x} = \pi^*_{2p_y} < \sigma^*_{2p}$

$O_{2}$ electron configuration (16e): $(\sigma_{1s})^2 (\sigma^*_{1s})^2 (\sigma_{2s})^2 (\sigma^*_{2s})^2 (\sigma_{2p})^2 (\pi_{2p})^4 (\pi^*_{2p})^2$

• Bonding: 10; Antibonding: 6; BO = (10−6)/2 = 2; Paramagnetic (2 unpaired in π*2p)

Bond Order Summary Table

Visual Reference

Molecular Orbital Diagram — $N_{2}$

Energy →

N atom MOs ($N_{2}$) N atom

1s 2s 2p 1s 2s 2p ↑↓ σ1s (2$e^{-}$) ↑↓ σ*1s (2$e^{-}$) ↑↓ σ2s (2$e^{-}$) ↑↓ σ*2s (2$e^{-}$) ↑↓ π2p ↑↓ π2p (4$e^{-}$) ↑↓ σ2p (2$e^{-}$) π*2p (0$e^{-}$) σ*2p (0$e^{-}$) $N_{2}$ (Z≤7): π2p fills BEFORE σ2p

Bond Order = (Nb − Na)/2 = (10 − 4)/2 = 3 (triple bond)

Source: Wikimedia Commons — Dinitrogen MO diagram ($N_{2}$)