MO Diagrams for Heteronuclear Diatomic Molecules

  1. I'm trying to understand how to draw MO diagram for molecules such as CO, HF, and NO. I am finding so much conflicting information on how to order the σ and pi boxes in the diagram. Now, I know that the more electronegative atom's orbitals are going to be lower in energy than the less electronegative atom.

    I have learned so far that there are two ways to set up MO diagrams for homo-nuclear diatomic molecules: one was with the pi 2p bonding MO below the σ2p bonding orbital and the reverse for atoms with an atomic number ≥8. How can this be applied to heteronuclear molecules? I keep finding different sources using both ways:



    Are both correct then?

  2. jcsd
  3. DrDu

    DrDu 4,421
    Science Advisor

    The correct order of the orbitals depends on the s-p energy gap in both atoms, the relative energetic distance of the s and p orbitals on both atoms, respectively, the orbital overlapp etc. So to obtain the correct ordering will require a calculation.
    You may try this yourself using e.g. some Extended Hueckel Calculators:

    On the other hand, the correct ordering is often not important, e.g. when both orbitals whose relative energy is unclear are both occupied.
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