Energy Level differences depending on Z

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Swati_Sharma_2D
Posts: 21
Joined: Wed Sep 21, 2016 2:59 pm

Energy Level differences depending on Z

Postby Swati_Sharma_2D » Fri Nov 04, 2016 9:47 pm

Can someone explain why the pi 2p energy level has less energy than the sigma 2p orbital when Z <8 and why the pi 2p energy level has more energy when Z>8? I understand that that is the case, but I don't understand why.

Caitlin Dillon 3G
Posts: 26
Joined: Wed Sep 21, 2016 2:56 pm

Re: Energy Level differences depending on Z

Postby Caitlin Dillon 3G » Sat Nov 05, 2016 2:44 pm

the course reader explains this on page 110.
Because the nuclear charge is less for atoms z<8, the energy difference between filled s-orbitals and p-orbitals is less.
The electron density from filled sigma(2s) and sigma*(2s) orbitals is concentrated along the bond axis.
Since the sigma(2Pz) orbitals is also directed along bond axis there is electron-electron repulsion resulting in a higher energy sigma(2Pz) orbital.
The sigma(2Pz) orbital is therefore above the pi(2Px) and pi(2Py) orbitals. (Remember electron density in a pi-orbital is concentrated away from the bond axis)


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