Looking at an CN2- molecule, we would expect sigma bonds. But when I make the energy diagram, I take an electron and add it since there is a negative two charge with this molecule. Yet looking at my answer key (attached) I see that instead the energy diagram only takes the diagram between N and C. Do we not add the electron when finding the bond information using the energy diagram? That would make sense since the lewis structure suggests it only has sigma bonds, but why do we not add an electron like we do for CN-? Attached is the key I refer to and a picture of the diagram for Cn-.
My exam is tomorrow so if you have any helpful advice for this problem please give it! Thanks