Hydrogen is a colorless gas with an atomic number of 1 and an atomic weight of 1.008. Hydrogen has a melting point of minus 259.2 degrees Celsius and a boiling point of minus 252.762 degrees Celsius.
Hydrogen, discovered in 1766, is the first and lightest element on the periodic table of the elements. It has a single electron, and the most common form of hydrogen, sometimes called protium, contains a single proton and no neutrons. Hydrogen has two other isotopes or variations with different numbers of neutrons. Deuterium has one neutron, and tritium has two neutrons. Deuterium and tritium both have use as tracer elements. Tritium is a component of luminescent paints and dyes as well as plays a part in the production of hydrogen bombs.
At normal temperatures and air pressures, hydrogen exists as a colorless, nontoxic, combustible gas with no taste or odor. Hydrogen typically exists as a diatomic molecule, a molecule consisting of two atoms. Hydrogen is the most common element in the universe, accounting for approximately 75 percent of the universe's elemental mass. Despite hydrogen's abundance in the universe as a whole, it is not common on Earth.
The combustibility of hydrogen makes it useful as a fuel source, especially for space shuttles. It also makes hydrogen potentially dangerous. In 1937, an electric charge ignited leaking hydrogen gas on an airship, causing the Hindenburg disaster.