What is the bond energy for O (oxygen?

Why can't we use diatomic oxygen to hep us decide whether the sigma2p bond or pi2p bond is lower in energy?

• Consider two molecular orbital energy diagrams, one in which sigma2p is lower in energy than pi2p and the other where pi2p is lower in energy than sigma2p. Because B2 is paramagnetic which diagram should be used? Why can't we use diatomic oxygen to hep us decide whether the sigma2p bond or pi2p bond is lower in energy?

• Answer:

  Diatomic oxygen is a bi-radical. The O-O bond is too long for a complete overlap of the p-orbitals in an SP2 hybrid model (though shorter than a single bond in a SP3 hybrid model). The two p-orbitals remain mostly separate, with a single free electron in either. Not as free as in true radicals, though. In short, we can't use diatomic oxygen as an example for a double bond because it doesn't have (a typical) one.