Ok so here's the problem: say I'm a sodium atom. It is 'charged' at +1e. A partner Chlorine atom is flying about, also 'charged' at -1e. According to chemistry (or rather the measurement of the reaction) energy is released if the two bond together.
The problem is, no electrons changed energy states. Both electrons in the shared band have the same state as before. I've heard a number of conflicting answers. One is that since the extra space is given to the shared electrons, there is a relaxing of the shared electrons which gives energy. That makes sense, but I have a few more questions:
Why is a valence band such a limiting factor? Not all atoms bond together to share electrons, mainly just the ones closest to a full shell, yet why does the atom care? Shouldn't the extra space for the electrons always be a good thing? Why do covalent reactions occur solely for these atoms with near-perfect valence shells?
Also, sometimes atoms just swap electon partners, in redox reactions specifically. Why do opposite spins attract heavily enough to do work against the coulomb potential? Also, even if electrons with opposite spin attract, since when do we forget the coulomb attraction? That is, electrons repel each other on the average.
Too many questions? That's fine. Let's also have too many answers. I want a clear and well-explained response, and would not encourage a rushed reply. Thank you.