What causes an electron to move from a group 1 element to a group 17? I understand that opposite charges attract, but why would the valence electron of sodium be more attracted to the nucleus of chlorine than its own? It seems strange that this occurs if the radius of a chlorine element is so much greater than that of sodium. Doesn't electrical force decrease at a rate equal to the inverse of square of the distance from the nucleus? Also, do we understand why electrons exist in specific energy levels? As opposed to anywhere like planetary orbits. Is this one of those quantum physics realms where I would have to understand the mathematics? Thanks in advance for any help with either question.