Molecular Orbitals

Molecular Orbitals Definition:

Molecular Orbitals, as introduced in the molecular orbital theory, are orbitals associated with an entire molecule rather than an individual atom.

Molecular Orbitals Explained:

Points to note about molecular orbitals –

  • Molecular orbitals are formed by the interaction of atomic orbitals. More specifically, when atomic orbitals with similar energies and proper symmetry spatially overlap each other.
  • Just as the atomic orbitals help us understand atoms, the molecular orbitals help us understand the structure of the molecule.
  • Since orbitals are wavefunctions, constructive interference gives rise to the bonding molecular orbitals while destructive interference gives rise to antibonding molecular orbitals.
  • Molecular orbitals may be empty or contain almost two electrons. The electrons first occupy molecular orbital that is lowest in energy (most stable). When occupying molecular orbitals, electrons follow both the Hund’s rule as well as Pauli’s exclusion principle.
  • When irradiated by UV light, the molecule absorbs energy and may promote an electron into its anti-bonding orbital. The filling of lower molecular orbital indicates that the molecule is stable compared to two individual atoms.
  • The highest occupied molecular orbital is known as HOMO.
  • The lowest unoccupied molecular orbital is known as LUMO.

Examples –

  • (Left) MO’s formed by the interaction of s-atomic orbitals. Notice, s- orbitals form sigma bonds only.
  • (Right) MO’s formed by the interaction of p-atomic orbitals. Note, p-orbitals form sigma as well as pi-bonds.

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