Question

. The molecular orbital configuration of molecules having atomic number less than 14 and more than 14 is different. Why?
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Answer 1

Explanation:

Among atoms with 14 or less electrons, I was told that the MO model is distinct from that used in the atoms with 15 or more electrons.

For N2 the orbitals in increasing energy are: σ1s<σ∗1s<σ2s<σ∗2s<π2px,π2py<σ2pz<π∗2px,π∗2py<σ∗2pz because it has 14 electrons.

There are 15 electrons available for N2−. Is the MO diagram the same as the N2 diagram, or not?  

And because this is a perfect opportunity to ask why this disparity still occurs in orbital energies.