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Molecular orbitals

Molecular orbital diagram of C₂

Bond order 2, diamagnetic. 12 electrons: Nb = 8, Na = 4.

CC
  • C

C₂Carbon

Bond order 2

12 electrons, all paired

i

Both bonds of the double bond in C2 are pi bonds, as NCERT points out; it is found in the vapour.

  • Bond order2
  • Magnetismdiamagnetic
  • Electrons12

Molecular orbitals

12 electrons
2bond order
diamagnetic

(Nb − Na) / 2 = (8 − 4) / 2

1s1s2s2s2p2pσ1sσ*1sσ2sσ*2sπ2pσ2pzπ*2pσ*2pzC atomMoleculeC atomEnergy

σ1s² σ*1s² σ2s² σ*2s² (π2px² = π2py²)

Working

Filling the diagram

  1. C₂ has 12 electrons: 6 from each C.
  2. Up to N₂ (and its ions), the π2p pair lies below σ2pz and fills first.
  3. Configuration: σ1s² σ*1s² σ2s² σ*2s² (π2px² = π2py²)
  4. Bonding electrons Nb = 8, antibonding electrons Na = 4.
  5. Bond order = (Nb − Na) / 2 = (8 − 4) / 2 = 2.
  6. Every electron is paired, so C₂ is diamagnetic.

Class 11, Chapter 4 Chemical Bonding and Molecular Structure.

Questions

MO diagram of C2: quick answers

What is the molecular orbital configuration of C2?

σ1s² σ*1s² σ2s² σ*2s² (π2px² = π2py²). Up to N₂ (and its ions), the π2p pair lies below σ2pz and fills first.

What is the bond order of C2 from its MO diagram?

2: Nb = 8 and Na = 4, so (8 - 4) / 2 = 2. It is diamagnetic.

Why is σ2pz above π2p in C2?

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

Try any molecule