Why are the pi bonding molecular orbitals (#pi_(2p_x)#, #pi_(2p_y)#) lower in energy than sigma bonding molecular orbital (#sigma_(2p_z)#) in the MO diagram of the #"N"_2# molecule?
Because from right to left, the orbital mixing interaction between two compatible orbitals of similar energies decreases the energy of the lower-energy orbital (relative to what it would be without mixing) and increases the energy of the higher-energy orbital (relative to what it would be without mixing).
This effect is still barely present on
Not surprisingly, this effect is called orbital mixing, and the result of it enhances the bonding with additional electron stabilization. This is often shown for the second-period elements.
Therefore, the effects of the mixing become less and less significant from left to right.
Nitrogen is the last element in the second period for which the diminishing effects of the orbital mixing are still significant enough for the energies of the
At that point, the