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Hydrogen: the essentials
Note that while hydrogen is normally shown at the top of the Group 1 elements in the periodic table, the term "alkaline metal" refers to the Group 1 elements from lithium downwards and not 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. It is also the most abundant element in the earth's sun.
Hydrogen as water (H2O) is absolutely essential to life and it is present in all organic compounds. Hydrogen is the lightest gas. Hydrogen gas was used in lighter-than-air balloons for transport but is far too dangerous because of the fire risk (Hindenburg). It burns in air to form only water as waste product and if hydrogen could be made on sufficient scale from other than fossil fuels then there might be a possibility of a hydrogen economy.
CAS Registry ID : 1333-74-0
Hydrogen: historical information
Hydrogen was discovered by  Henry Cavendish in 1766 at  London, England. Origin of name : from the Greek words "hydro" and "genes" meaning "water" and "generator".
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.]
In 1839 a British scientist Sir William Robert Grove carried out experiments on electrolysis. He used electricity to split water into hydrogen and oxygen. He then argued one should be able to reverse the electrolysis and so generate electricity from the reaction of oxygen with hydrogen. He enclosed platinum strips in separate sealed bottles, one containing hydrogen and one oxygen. When the containers were immersed in dilute sulphuric acid a current indeed flowed between the two electrodes and water was formed in the gas bottles. He linked several of these devices in series to increase the voltage produced in a gas battery. Later the term fuel cell was used by the chemists Ludwig Mond and Charles Langer.
In 1932 Dr Francis Thomas Bacon, an engineer at Cambridge University in the UK, worked further on designs of Mond and Langer. He replaced the platinum electrodes with less expensive nickel gauze and substituted the sulphuric acid electrolyte for alkaline potassium hydroxide (less corrosive to the electrodes). This was in essence the first alkaline fuel cell (AFC) and was called the Bacon Cell. It took Bacon another 27 years to demonstrate a machine capable of producing 5 kW of power, enough to power a welding machine. At about the same time the first fuel cell powered vehicle was demonstrated.
Much later fuel cells were by NASA in the 1960s for the Apollo space missions. Fuel cells have been used for more than 100 missions in NASA spacecraft. Fuel cells are also used in submarines.
The lifting agent for the ill fated Hindenberg ballooon was hydrogen rather than the safer helium. The image below is the scene probably in a way you have not seen it before. This is a "ray-traced" image reproduced with the permission of Johannes Ewers , the artist, who won first place with this image in the March/April 1999 Internet Raytracing Competition . For details of ray-tracing you can't beat the POV-Ray site.
Hydrogen around us
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Hydrogen makes up two of the three atoms in water and water is absolutely essential to life. Hydrogen is present in all organic compounds. A form of water in which both hydrogen atoms are replaced by deuterium (2H, or D) is called "heavy water" (D2O) and is toxic to mammals. Some bacteria are known to metabolise molecular hydrogen (H2).
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.
Abundances for hydrogen in a number of different environments. More abundance data »
Location
Second ionisation energy : (no data) kJ mol‑1
Isolation
Isolation : in the laboratory, small amounts of hydrogen gas may be made by the reaction of calcium hydride with water.
CaH2 + 2H2O → Ca(OH)2 + 2H2
This is quite efficient in the sense that 50% of the hydrogen produced comes from water. Another very convenient laboratory scale experiment follows Boyle's early synthesis, the reaction of iron filings with dilute sulphuric acid.
Fe + H2SO4 → FeSO4 + H2
There are many industrial methods for the production of hydrogen and that used will depend upon local factors such as the quantity required and the raw materials to hand. Two processes in use involve heating coke with steam in the water gas shift reaction or hydrocarbons such as methane with steam.
CH4 + H2O (1100°C) → CO + 3H2
C(coke) + H2O (1000°C) → CO + H2
In both these cases, further hydrogen may be made by passing the CO and steam over hot (400°C) iron oxide or cobalt oxide.
CO + H2O → CO2 + H2
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The Hydrogen isotope H-2, also known as deuterium, is used in a variety of applications. Deuterium is used extensively in organic chemistry in order to study chemical reactions. It is also used in vitamin research. Deuterium in the form of H2O, known as heavy water, is used as a moderator in CANDU nuclear reactors, in NMR studies and in studies into human metabolism. Heavy water is also applied in the Sudbury Neutrino Observatory where it is used to study the behavior of neutrinos.