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Molecular orbitals

Molecular orbital diagram of He₂

Bond order 0, diamagnetic. 4 electrons: Nb = 2, Na = 2.

HeHe
  • He

He₂Helium (two atoms)

Bond order 0

4 electrons, all paired

i

Bond order zero: He2 does not exist as a molecule.

  • Bond order0
  • Magnetismdiamagnetic
  • Electrons4

Molecular orbitals

4 electrons
0bond order
diamagnetic

(Nb − Na) / 2 = (2 − 2) / 2

1s1sσ1sσ*1sHe atomMoleculeHe atomEnergy

σ1s² σ*1s²

Working

Filling the diagram

  1. He₂ has 4 electrons: 2 from each He.
  2. Configuration: σ1s² σ*1s²
  3. Bonding electrons Nb = 2, antibonding electrons Na = 2.
  4. Bond order = (Nb − Na) / 2 = (2 − 2) / 2 = 0.
  5. Every electron is paired, so He₂ is diamagnetic.
  6. A bond order of zero means there is no bond: He₂ is not a stable molecule.

Class 11, Chapter 4 Chemical Bonding and Molecular Structure.

Questions

MO diagram of He2: quick answers

What is the molecular orbital configuration of He2?

σ1s² σ*1s². Configuration: σ1s² σ*1s²

What is the bond order of He2 from its MO diagram?

0: Nb = 2 and Na = 2, so (2 - 2) / 2 = 0. It is diamagnetic.

Why is σ2pz above π2p in He2?

Up to N2 the 2s and 2p orbitals are close in energy and mix, which pushes σ2pz above the π2p pair.

Try any molecule