MO diagram  [ENDORSED]

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MO diagram

Postby Angela_Kim_1N » 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.

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Re: MO diagram  [ENDORSED]

Postby Helen_Onuffer_1A » 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.

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Re: MO diagram

Postby Tiffany_Hoang_3C » 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.

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