Why are the valence electrons of an atom the only electrons likely to be inolved in bonding to other atoms?

Answer 1

The core (non-valence) electrons are already in a stable, low-energy configuration. If you were to disturb that by bonding, you would need to provide lots of energy.

Answer 2

I think you may be confused: you're probably refering to the annotations 'anion and cation' which describe the balance in the octet (which is simply described in the Britanica) but when atoms bond in colour chemistry, which is where I specialize, its because enviornmental conditions force the elements into conjunction, from there it's a matter of centrifugal force and gravity that determine bonding patterns.

Answer 3

Because they are the outermost electrons, and therefore they are the ones that actually "contact" other atoms. Actually, electrons occupy orbitals, and therefore it's the orbitals that matter. In particular, there is a frontier orbital treatment that explains a lot of chemistry. The electrons in the highest occupied molecular orbitals (HOMO) donate electrons into the lowest unoccupied molecular orbitals (LUMO). "Highest" and "lowest" refers to energy.