Molecular orbital diagram of CO

(Nb − Na) / 2 = (10 − 4) / 2

σ1s² σ*1s² σ2s² σ*2s² (π2px² = π2py²) σ2pz²

1. C has 4 valence electrons. In the Lewis structure it makes one triple bond to O and keeps one lone pair, which leaves it a formal charge of −1.
2. Steric number = one sigma bond + one lone pair = 2, so C is sp hybridised. A double or triple bond counts once: only its sigma bond uses a hybrid orbital.
3. Two electron pairs point in opposite directions, along a line (linear electron geometry). With only two atoms, the molecule itself is a straight line.
4. Two atoms always lie on a straight line, so there is no bond angle.
5. The two atoms are different, so the bond is polar and so is CO.

Formal charges: C −1, O +1