MO diagrams: N₂ and O₂ template

Valence MO diagrams of N₂ (s–p mixing, σ2p above π2p, bond order 3, diamagnetic) and O₂ (two unpaired electrons in π*2p, bond order 2, paramagnetic).

What the template shows

• Second-row diatomics: the order of σ2p and π2p changes between N₂ and O₂
• Dinitrogen (s–p mixing)
• For Li₂ to N₂, 2s–2p mixing pushes σ2p above π2p. Valence orbitals only (1s core not shown)
• Bond order = ½ (8 − 2) = 3
• diamagnetic (all electrons paired)
• For O₂ and F₂ the order is σ2p below π2p. The last two electrons go one each into the two π*2p orbitals
• Bond order = ½ (8 − 4) = 2
• paramagnetic (2 unpaired e⁻)
• N₂: 10 valence electrons, bond order 3, all paired: diamagnetic. The N≡N bond (945 kJ mol⁻¹) is one of the strongest known.
• O₂: 12 valence electrons; Hund's rule puts the last two in separate π*2p orbitals with parallel spins, so O₂ is paramagnetic (a Lewis structure cannot show this).
• s–p mixing (strong when 2s and 2p are close in energy, Li to N) raises σ2p above π2p; for O₂ and F₂ the gap is large and σ2p lies lower.
• Removing an antibonding electron strengthens the bond: O₂⁺ has bond order 2.5; adding one weakens it: O₂⁻ (superoxide) 1.5.
• Every part of this figure is editable · sources on the template card

Drawn with 437 shapes – every one editable in MolDraw.

Sources

• Miessler, Fischer & Tarr, Inorganic Chemistry, 5th ed., Pearson 2014, ch. 5 Textbook
• Housecroft & Sharpe, Inorganic Chemistry, 5th ed., Pearson 2018, ch. 2 Textbook
• Atkins, de Paula & Keeler, Atkins' Physical Chemistry, 11th ed., OUP 2018, ch. 9 Textbook