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Molecular orbitals

Molecular orbital diagram of Li₂

Bond order 1, diamagnetic. 6 electrons: Nb = 4, Na = 2.

LiLi
  • Li

Li₂Lithium

Bond order 1

6 electrons, all paired

i

Li2 exists in the vapour.

  • Bond order1
  • Magnetismdiamagnetic
  • Electrons6

Molecular orbitals

6 electrons
1bond order
diamagnetic

(Nb − Na) / 2 = (4 − 2) / 2

1s1s2s2sσ1sσ*1sσ2sσ*2sLi atomMoleculeLi atomEnergy

σ1s² σ*1s² σ2s²

Working

Filling the diagram

  1. Li₂ has 6 electrons: 3 from each Li.
  2. Up to N₂ (and its ions), the π2p pair lies below σ2pz and fills first.
  3. Configuration: σ1s² σ*1s² σ2s²
  4. Bonding electrons Nb = 4, antibonding electrons Na = 2.
  5. Bond order = (Nb − Na) / 2 = (4 − 2) / 2 = 1.
  6. Every electron is paired, so Li₂ is diamagnetic.

Class 11, Chapter 4 Chemical Bonding and Molecular Structure.

Questions

MO diagram of Li2: quick answers

What is the molecular orbital configuration of Li2?

σ1s² σ*1s² σ2s². Up to N₂ (and its ions), the π2p pair lies below σ2pz and fills first.

What is the bond order of Li2 from its MO diagram?

1: Nb = 4 and Na = 2, so (4 - 2) / 2 = 1. It is diamagnetic.

Why is σ2pz above π2p in Li2?

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

Try any molecule