Hydrogen

Hydrogen is the lightest element. It is by far the most abundant element in the universe and makes up about about 90% of the universe by weight. Hydrogen as water (H2O) is absolutely essential to life and it is present in all organic compounds. Hydrogen gas was used in lighter-than-air balloons for transport but is far too dangerous because of the fire risk (Hindenburg).

commercial fixation of nitrogen from the air in the Haber ammonia process

hydrogenation of fats and oils

methanol production, in hydrodealkylation, hydrocracking, and hydrodesulphurization

rocket fuel

welding

production of hydrochloric acid

reduction of metallic ores

for filling balloons (hydrogen gas much lighter than air; however it ignites easily)

liquid H2 is important in cryogenics and in the study of superconductivity since its melting point is only just above absolute zero

One of hydrogen's isotopes, tritium (3H) is radioactive. Tritium is produced in nuclear reactors and is used in the production of the hydrogen bomb. It is also used as a radioactive agent in making luminous paints and as a tracer isotope.

Robert Boyle (1627-1691; English chemist and physicist) published a paper ("New experiments touching the relation betwixt flame and air") in 1671 in which he described the reaction between iron filings and dilute acids which results in the evolution of gaseous hydrogen ("inflammable solution of Mars" [iron]).

However it was only much later that it was recognized as an element by Henry Cavendish (1731-1810; an English chemist and physicist who also independently discovered nitrogen) in 1766 when he collected it over mercury and described it as "inflammable air from metals". Cavendish described accurately hydrogen's properties but thought erroneously that the gas originated from the metal rather than from the acid. Hydrogen was named by Lavoisier.

Deuterium gas (2H2, often written D2), made up from deuterium, a heavy isotope of hydrogen, was discovered in 1931 by Harold Urey, a professor of chemistry at Chicago and California (both USA).

Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for hydrogen is shown below. [See History of Chemistry, Sir Edward Thorpe, volume 1, Watts & Co, London, 1914.]

H2 gas is present in the earth's atmosphere in very small quantities, but is present to a far greater extent chemically bound as water (H2O) Water is a constituent of many minerals.

Hydrogen is the lightest element and is by far the most abundant element in the universe, making up about about 90% of the atoms or 75% of the mass, of the universe. Hydrogen is a major constituent of the the sun and most stars. The sun burns by a number of nuclear processes but mainly through the fusion of hydrogen nuclei into helium nuclei. Hydrogen is a major component of the planet Jupiter. In the planet's interior the pressure is probably so great that solid molecular hydrogen is converted into solid metallic hydrogen.