From the Greek word hydro (water), and genes (forming). Hydrogen was recognized as a distinct substance by Henry Cavendish in 1776. Diagram of a simple hydrogen atom.
Hydrogen is the most abundant of all elements in the universe. The heavier elements were originally made from hydrogen atoms or from other elements that were originally made from hydrogen atoms.
Great quantities of hydrogen are required commercially for nitrogen fixation using the Haber ammonia process, and for the hydrogenation of fats and oils. It is also used in large quantities in methanol production, in hydrodealkylation, hydrocracking, and hydrodesulfurization. Other uses include rocket fuel, welding, producing hydrochloric acid, reducing metallic ores, and filling balloons.
The lifting power of 1 cubic foot of hydrogen gas is about 0.07 lb at °C, 760 mm pressure.
The hydrogen fuel cell is a developing technology that will allow great amounts of electrical power to be obtained using a source of hydrogen gas.
Consideration is being given to an entire economy based on solar- and nuclear-generated hydrogen. Public acceptance, high capital investment, and the high cost of hydrogen with respect to today's fuels are but a few of the problems facing such an economy. Located in remote regions, power plants would electrolyze seawater; the hydrogen produced would travel to distant cities by pipelines. Pollution-free hydrogen could replace natural gas, gasoline, etc., and could serve as a reducing agent in metallurgy, chemical processing, refining, etc. It could also be used to convert trash into methane and ethylene.
Quite apart from isotopes, it has been shown that under ordinary conditions hydrogen gas is a mixture of two kinds of molecules, known as ortho- and para-hydrogen, which differ from one another by the spins of their electrons and nuclei.
Normal hydrogen at room temperature contains 25% of the para form and 75% of the ortho form. The ortho form cannot be prepared in the pure state. Since the two forms differ in energy, the physical properties also differ. The melting and boiling points of parahydrogen are about 0.1�C lower than those of normal hydrogen.