z<8 and z>8

[Jennifer_Lam_1A]

When do you use when z>8 and z<8 for the molecular orbital diagram? What exactly is z?

[Kiana_Shibata_2G]

z is an atom's atomic number and the less than and greater than have to do with whether the sigma bond is lower or higher than the first pi bond in the 2nd energy level in molecular orbitals. If z<8, than the sigma 2p bond is greater in energy than the pi 2p bond so it will be higher. And vice versa for greater or equal to 8. The sigma sp bond is lower than the pi 2p bond.