Molecular orbital theory (advanced)
Quantum Chemistry (UG) · Chemistry
Study notes
Use MO theory to predict whether He₂ exists and whether O₂ is magnetic. Step 1: He₂ would be (σ1s)²(σ*1s)²: bond order = ½(2-2) = 0 → no bond, He₂ doesn't exist. Step 2: O₂ has 12 valence electrons: (σ2s)²(σ*2s)²(σ2p)²(π2p)⁴(π*2p)². Step 3: Bond order = ½(8-4) = 2 → double bond, matches experiment. Step 4: Two unpaired electrons in π* → paramagnetic. Liquid O₂ sticks to a magnet — MO theory predicted this!