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MO Diagram difference

Posted: Tue Nov 08, 2016 4:59 pm
by Jose_Arambulo_2I
I'm still unclear as to why the sigma p orbitals and pi p orbitals switch depending on nuclear charge. What exactly causes this to take place?

Re: MO Diagram difference

Posted: Tue Nov 08, 2016 8:55 pm
by Kathy Vu 3L
It has to deal with electron repulsion. For z<8, π2p MO’s are filled before the σ2p MO because there is less electron-electron repulsion between the π2p and the σ2s and the σ2s*. For z>8, σ2s and σ2s* MO’s are closer because greater nuclear charge, therefore the σ2p MO's will react less strongly with them and be lower in energy than the π2p MO’s.