[Sophia7X]

How come the configuration of F₂⁺ is (σ_2s)²(σ_2s*)²(σ_2p)²(π_2p)⁴(π_2p*)³ instead of (σ_2s)²(σ_2s*)²(σ_2p)²(π_2p)⁴(π_2p*)²(σ_2p*)¹?

I thought orbitals had to be singly occupied before you pair up electrons.

[Dan]

I thought orbitals had to be singly occupied before you pair up electrons.

σ_2p* is higher in energy than π_2p*, so it is more energetically demanding to fill the former before pairing up in the latter.

Consider the electronic configuration of F₂:



Now remove an electron from the HOMO and you have the ground state of F₂⁺.

[Sophia7X]

Oh, I've been filling in the orbitals incorrectly. So you only put one electron in each orbital of the same energy before doubling up then occupying a higher orbital?

[Dan]

So you only put one electron in each orbital of the same energy before doubling up then occupying a higher orbital?

Yes, see: http://en.wikipedia.org/wiki/Molecular_orbital_diagram#Basics