First of all, I want to discuss the whole thing strictly according to the VB - theory and not use any concepts of the MO - theory.
According to Linus Pauling, the "3 electron Bond" is the resonance of one electron between 2 half filled orbitals:
A| •B <-> A• |B
I use his representation: "A•••B".
I applied that Idea to Triplett Oxygen, which has one sigma bond and 2 x ½ π Bonds or "2 x 3 electron bonds": "O÷÷÷O" so it forms one sigma Bond between the two half filled 2py orbitals and two ½ π Bonds between
- one fully occupied 2px orbital and one half filled 2pz orbital.
- one half filled 2pz orbital and one fully occupied 2px orbital
Then I moved on to Peroxid with O2--.
I now have two options:
- Starting with the following electron configuration: O: 2s² 2px² 2py¹ 2pz¹, O--: 2s² 2px² 2py² 2pz²
That must lead to two "3 electron bonds": "O:::O".
- Starting with the following electron configuration: O-: 2s² 2px² 2py² 2pz¹, O-: 2s² 2px² 2py² 2pz¹
That must lead to one sigma bond: "O-O".
I know that it can't be option one because Peroxide is diamagnetic and probably more energetically favourable to form a single sigma bond than two ½ π Bonds, but is there another explanation for that?
I also tried to apply that on Dioxygenyl, and endet up with one sigma bond, one π bond and one ½ π Bond: "O=•••O":
But then I didn't have to face this question because I could only start with O and O+ or O+ and O.