D2O, 2 Deuterium, and 1 Oxygenatom. Deuterium is an isotope of hydrogen; it has one extra neutronin the nucleus. Neutrons are what add weight to an atom; this substance is called "Heavy Water" as compared to normal "Light Water." Heavy water exists is most all water, but only in very small amounts (1 in 20 million).
Heavy water is essential to nuclearpower using non-enriched uranium. Without it, all uranium must be enriched before use. In WW-II, Hitler attacked Norwayfor it’s supply of heavy water.
