Isotopes of hydrogen
Isotopes are the different forms of the same element, which have the same atomic number but different mass numbers. The isotopes of hydrogen are protium, deuterium and tritium with mass number 1, 2 and 3 respectively. The relative abundance of three isotopes in nature is in the ratio of 1 : 1.5 x 10-2: 1 x 10-17respectively. The hydrogen occurring in nature is mainly composed of atoms of protium and it contains only 0.015% of deuterium atoms. The third isotope of hydrogen is radioactive.