Key information
Atomic number: 
Atomic weight: 
71 kg/m³
Boiling point: 
20.46° K
Melting point: 
13.96° K
Alkali Metals

Hydrogen is the lightest of all elements, a colourless and odourless gas. The two stable isotopes of hydrogen occur in the Earth's atmosphere hydrogen in the ration of about 1 atom of deuterium to every 6,700 atoms of protium. A third hydrogen isotope, tritium, is a radioactive gas which occurs to a very limited extent in atmospheric hydrogen. Although hydrogen was prepared many years earlier, it was first recognized as a substance distinct from other flammable gases in 1766 by the British chemist and physicist Henry Cavendish (1731-1810). Antoine Laurent Lavoisier (1743-1794) repeated the experiments of Cavendish, whereby "inflammable air" was first isolated and then reacted with oxygen, in 1785, to produce a dew, which appeared to be water upon being burned. Lavoisier, who named the gas hydrogen found the element to be much less dense than air. Deuterium was discovered by H. C. Urey, F. G. Brickwedde, and G. M. Murphy in 1932. Tritium was synthesized by Ernest Rutherford, L. E. Oliphant, and Paul Harteck in 1935.

Manufacturing and Uses

Hydrogen is a feedstock for a large number of industrial chemicals. Ammonia used in the manufacture of fertilisers constitutes the largest volume of such material. The second largest by volume chemical derived from hydrogen is methanol. Manufacture of other chemicals: cyclohexanes, benzene, oxo-alcohols and anilines make up the balance of hydrogen use.

Hydrogen can be manufactured through hydrolysis of metal hydrides and electrolysis of an aqueous salt solution

CaH2 + H2O -> CaOH +H2


Salt + Water -> Chlorine + Sodium Hydroxide + Hydrogen
2NaCl (salt) + 2H2O (water) -> Cl2 (chlorine) + 2NaOH (sodium hydroxide) + H2 (hydrogen)

(Chlor-Alkali Process)

Refinery Gas
Hydrogen is also to be found in refinery gas together with methane, ethane and olefins. Refinery gas is defined as non-condensable gas obtained during distillation of crude oil or treatment of oil products (e.g. cracking) in refineries.

Electron Shell: 
Amazon Books
Image of Hydrogen: The Essential Element
Author: John S Rigden
Publisher: Harvard University Press (2003)
Binding: Paperback, 288 pages