Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Molecular Orbital energy levels

  1. Dec 11, 2011 #1
    Hi everyone
    I'm currently studying the MO theory and ran into some trouble understanding orbital energy levels.

    As I have previously read, σ bonds are stronger than ∏ bonds, therefore are lower in orbital energy. However, from the MO theory, the σ2p orbital is actually higher in energy than the ∏2p orbital in molecules like B2 and N2. But in molecules like O2 and F2, this sequence is reversed, with the ∏2p orbital having the higher orbital energy.

    Can anyone tell me why?
  2. jcsd
  3. Dec 12, 2011 #2


    User Avatar
    Science Advisor

    a) I think you are referring to the anti-bonding orbitals, not the bonding ones.
    b) the sigma bonds are not formed from pure p orbitals but from a superposition of 2s and 2p orbitals. The energetic distance of the 2s and 2p orbitals increases from left to right in a period, which explains the interchange of the energetic ordering of the molecular orbitals.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Molecular Orbital energy levels
  1. Molecular Orbitals (Replies: 1)

  2. Molecular Orbitals (Replies: 4)