Physical and chemical properties of water and heavy water;
Heavy water is water that contains the heavy isotope of hydrogen called deuterium (chemical symbol D). The deuterium atom weighs about twice as much as ordinary hydrogen atom. Heavy water, also called deuterium oxide, makes up about 1 part in 5000 of ordinary water.
It was first separated from ordinary water in 1932 by G N Lewis, a chemist at the University of California.
Because of the difference between the weights of the two kinds of hydrogen atoms, the physical properties of heavy water differ from those of ordinary water. Heavy water freezes at 3.82oC and boils at 101.42oC.
Ice made from heavy water sinks in normal water.
Heavy water is useful in some kinds of nuclear reactors. It acts as a moderator to control the energy of the neutrons in a chain reaction. Seeds will not germinate in heavy water, and some animals, including tadpoles, cannot live in it.