Hydrogen is the first element in the periodic table. Its symbol is H. It is the lightest element having only one proton and one electron. Hydrogen has three naturally occuring isotopes: 1H, known as protium is the most common by far, 2H is called deuterium, and 3H is called tritium. Hydrogen is the only element whose isotopes are given unique names - all other isotopes are simply named after their element, for example 14C is simply called carbon fourteen.
Pure hydrogen is a diatomic gas that is quite flammable. Because the combustion of hydrogen produces only water, it has gained attention as a non-polluting fuel for engines, especially in automobiles.