What I've never understood is how the atomic nuclei has such influence on macroscopic chemical properties. The only useful property of the nuclei is its charge - an integer number, so all macroscopic effects should be completely defined by that integer alone, and all properties of water are sufficiently described by just three numbers - 1, 8, 1 (in any order).
short version: the electrons assemble in asymmetric layers, conferring properties to the atoms. Thus the atoms on the same columns having comparable properties by having the same layers occupied by electrons.
and that's the "I flunked the exam" version, I'm sure this level of explanation is ridiculously simplified compared to the real deal ;)