[mana]

hi all
as you know, in B₂, C₂and N₂, the s and p atomic orbitals can interact but in O₂, F₂ and Ne₂, these orbitals can't interact due to small size of the atoms and also the different level of energy between s and p orbitals. so the  MO diagram is as follows, now my question is when an atom from the first group and an atom from the second group, have a bond, what would be the MO diagram shape? For example, I have attached the MO diagram of the C-O and N-O bond, can you explain to me why they are so different, and is there any rule or something to recognize the shape of MO diagrams for two heteroatoms?

[Corribus]

First, let's note that the MO diagram you have at left is the MO diagram of carbon dioxide, not carbon monoxide. You can tell this most easily because two s orbitals for oxygen are shown. You can see the appropriate MO diagram for CO here:

https://en.wikipedia.org/wiki/Carbon_monoxide#/media/File:MO_COeng.svg

That may help with your confusion.

Just in case not: Strictly speaking, atomic orbitals (AOs) on adjacent nuclei of appropriate symmetry have non-zero interaction in the LCAO-MO approach, but the degree of interaction depends a lot on the energy separation between the interacting AOs. As the energy gap increases, the degree of interaction decreases. It is usually assumed that MOs are formed predominantly by the two strongest AO interactions - in reality, ALL AOs of appropriate symmetry combine to form MOs, and if there are n AOs of symmetry class x, then they interact for form n MOs. Nevertheless, MO diagrams are usually depicted only showing the strongest pair of interactions that form each MO, although not always. This can cause some confusion when viewing MO diagrams that are taken from different sources.

If you still have questions, please ask for further clarification.