The three isotopes of hydrogen
The hydrogen atom has two isotopes: deuterium and tritium. The nucleus of hydrogen consists of one solitary proton, deuterium has one neutron as well as the proton and tritium contains one proton and two neutrons. The electrical charge on all three is the same, and the chemical properties are identical. There are also important differences, however. Deuterium is twice as heavy as hydrogen (and tritium is three times the mass), and is stable, though much rarer than hydrogen. Tritium, on the other hand, is unstable and radioactive