I wonder about this. The explanation that I keep finding is that "dipoles" occur "randomly" when "electrons move" to different sides of the atom. Yet I find this difficult to reconcile with what I understand about quantum mechanics -- so I must be missing something, on either side or both. In particular, in quantum mechanics electrons are not "moving" like classic particles as seems to be suggested by this "explanation", not unless you subscribe to those theories like Bohm's or similar, but rather are described by wave functions and the Schrodinger equation, and as far as I can tell these do not "randomly" "concentrate" in some fashion. How is this effect explained in a proper quantum-mechanical treatment, in a more mainline view of quantum theory? I've tried searching around but have not found anything satisfying.