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Posted: Wed Nov 09, 2016 8:41 pm
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
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
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.