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MO diagram

Posted: Wed Nov 09, 2016 8:41 pm
by Angela_Kim_1N
When drawing the molecular orbital diagram, why do we fill up the pi before the sigma?
For example, in the diagram for N2, pi2p would be filled up before sigma2p.

Re: MO diagram  [ENDORSED]

Posted: Wed Nov 09, 2016 9:21 pm
by Helen_Onuffer_1A
When Z < 8, the 2p pi bonds have a lower energy than the 2p sigma bonds so those get filled first since we fill the lowest energy levels first.

Re: MO diagram

Posted: Thu Nov 10, 2016 1:19 pm
by Tiffany_Hoang_3C
For Z < 8, because the nuclear charge is less, the energy difference between filled s-orbitals and p-orbitals is less. The e- density from filled sigma and sigma* orbitals is concentrated along the bond axis, resulting in electron-electron repulsion and thus, a higher energy sigma orbital.