[Mark S 2014]

Just started molecular orbital energy diagrams today. I'm looking at the diagrams for F₂. F has 5 electrons in the p orbitals. I don't get why the 3σ_u^* antibonding orbital has to be left empty, why not one of the 1Π_g^* anitbonding orbitals ? This implies that the p_z orbitals are filled last each time, but I thought the p orbitals where degenerate and could be filled in any order. Is it just convention that p_z orbitals are filled last, thus the energy diagram should always look the same ? Or in theory could for example both p_y orbitals each contain the single electron, leaving the 1Π_g^* orbital empty ?

[Mark S 2014]

Never mind, stupid quesiton. I undestand now, the question did not make sense - I misunderstood something.