[tech99]

If the electrons in s level are at a "low" energy level, how do they share electrons at p (higher energy level)?
For example: H (1s1) and O (2s2, 2px2, 2py1, 2pz1)
If H binds with other (heavier) elements I assume the difference will be even greater.

Can you provide an illustration of what happens?
Thanks 

[BluePill]

There is a concept in MO theory about symmetry and energy effects.

You see, it's not all about energy difference. You have to also consider if their symmetry would allow overlap of the AO to form MOs



Look at the MO diagram to see what I'm telling you. The AO Energy of H and AO Energy of F is a little off so the energy difference isn't that high and look at the shapes of the AO orbitals. Their symmetry can have an overlap.

This is only a descriptive description of AO mixing. If you want a quantitative one, I have an elaborate discussion which I could not summarize.