Heavy water is a form of water with a unique atomic structure ... atom is indeed heavier, with a neutron as well as a proton in its nucleus. This isotope of hydrogen is called deuterium, and ...

An element's atomic number defines it. An element with 17 protons will always be chlorine. However an element's mass numbers can vary, which means that it can have different numbers of neutrons.

There are three isotopes of hydrogen: hydrogen, deuterium (hydrogen-2) and tritium (hydrogen-3): if the atom loses one or more electrons, it becomes a positively-charged ion if the atom gains one ...