Answer: Atomic nuclei are positively charged; thus each nucleus repels each other nucleus. In order to fuse two nuclei together, they must be brought very close together, so that the strong (but short-range) nuclear force that holds nuclei together can do its work.Since the hydrogen electrons are spending most of their time around the oxygen atom, the hydrogen atoms, which have one proton each, take on a partially positive charge. This results in a polar molecule (a molecule that has partially positive & negative regions).
