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Molecular orbitals

Molecular orbital diagram of NO

Bond order 2.5, paramagnetic. 15 electrons: Nb = 10, Na = 5.

ON
  • N
  • O

NONitric oxide

Bond order 2.5

15 electrons, 1 unpaired

i

NO has an odd number of electrons, so one is always unpaired.

  • Bond order2.5
  • Magnetismparamagnetic
  • Electrons15

Molecular orbitals

15 electrons
2.5bond order
paramagnetic

(Nb − Na) / 2 = (10 − 5) / 2

1s1s2s2s2p2pσ1sσ*1sσ2sσ*2sσ2pzπ2pπ*2pσ*2pzN atomMoleculeO atomEnergy

σ1s² σ*1s² σ2s² σ*2s² σ2pz² (π2px² = π2py²) (π*2px¹ = π*2py⁰)

Working

Filling the diagram

  1. NO has 15 electrons: 7 from N and 8 from O.
  2. With more than 14 electrons, σ2pz lies below the π2p pair and fills first.
  3. Configuration: σ1s² σ*1s² σ2s² σ*2s² σ2pz² (π2px² = π2py²) (π*2px¹ = π*2py⁰)
  4. Bonding electrons Nb = 10, antibonding electrons Na = 5.
  5. Bond order = (Nb − Na) / 2 = (10 − 5) / 2 = 2.5.
  6. One electron is unpaired (in one of the π*2p orbitals), so NO is paramagnetic.

Class 11, Chapter 4 Chemical Bonding and Molecular Structure.

Questions

MO diagram of NO: quick answers

What is the molecular orbital configuration of NO?

σ1s² σ*1s² σ2s² σ*2s² σ2pz² (π2px² = π2py²) (π*2px¹ = π*2py⁰). With more than 14 electrons, σ2pz lies below the π2p pair and fills first.

What is the bond order of NO from its MO diagram?

2.5: Nb = 10 and Na = 5, so (10 - 5) / 2 = 2.5. It is paramagnetic.

Why is σ2pz below π2p in NO?

From O2 onwards the 2s and 2p orbitals are far apart in energy and hardly mix, so σ2pz stays below the π2p pair.

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