M.O

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Jake Ney lecture 1 discussion 1F
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Joined: Fri Sep 25, 2015 3:00 am

M.O

Postby Jake Ney lecture 1 discussion 1F » Sat Dec 05, 2015 2:05 pm

In creating molecular orbital diagrams, why do molecules with an atomic number less than 8 have a notation with a Pi first in the P orbital while molecules with an atomic number greater than 8 have the Sigma orbital first? What would be the correct notation for a molecule such as C-F?

Umair Khan 2G
Posts: 32
Joined: Fri Sep 25, 2015 3:00 am

Re: M.O

Postby Umair Khan 2G » Sat Dec 05, 2015 2:35 pm

When your nuclear charge (the z value, also known as the atomic value) is less than 8 the energy difference between the pi is sigma is so close to each other that the pi is filled first. As you go across the periodic table and down groups, the energy difference between sigma and pi grows, and sigma fills before pi because it is lower in energy.
When drawing out molecular orbitals, we always look for which element has the lowest nuclear charge as base are drawing off that.
For C-F, since carbon has a z value of less than 8, we draw the pi orbitals as having less energy, or lower than sigma.


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