TR

Valence Bond Theory and Hybridization

  • 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