• In valence bond theory, bonds result from the pairing of unpaired electrons from the valence shell atomic orbitals

• σ bond: cylindrically symmetric about the bond axis; no nodal plane along the bond axis

• 𝜋 bond: electron density in 2 lobes with a single nodal plane along the bond axis

• Single bond: 𝜋 bond

• Double bond: σ bond + 𝜋 bond

  • Molecules can’t rotate around a double bond

• Triple bond: σ bond + 𝜋 bond + 𝜋 bond

Electron Promotion and Hybridization of Atomic Structures

• Electron promotion serves to increase the number of unpaired electrons

  • If you have an empty orbital you can promote one of your electrons to that orbital

• The hybrid orbitals only differ in their orientation in space

• Energy for the initial electron promotion comes from bonding

• (# of bonded atoms) + (# of lone pairs) = # of hybrid orbitals

• 2 hybrid orbitals = sp

• 3 hybrid orbitals = sp²

• 4 hybrid orbitals = sp³

• Exception: single-bonded terminal atoms

• Don’t hybridize single-bonded terminal atoms