Hydrogen is the most abundant element in the universe (see elements, cosmic abundance) and one of the most important to life as we know it.
Hydrogen atoms are the least massive of all atoms. The lightest and most common isotope of hydrogen, 1H, is known as protium and consists of one proton and one electron. Two other isotopes of hydrogen exist. They are deuterium, or "heavy hydrogen", with a nucleus containing one neutron and one proton, and radioactive tritium with a nucleus containing two neutrons and one proton. Hydrogen is the only element whose isotopes have been given different names.
Chemistry of hydrogenHydrogen is fairly reactive, giving hydrides with most other elements on heating, and a moderate reducing agent. It belongs in no definite group in the periodic table, but has some resemblance to the halogens in forming the ion H-, and to the alkali metals in forming the ion H+ (see acid); it is always monovalent. See also hydrogen bond.
Uses of hydrogenLarge amounts of hydrogen are used commercially for making ammonia by the Haber process, and for the hydrogenation of fats and oils. It is also used in methanol production, in hydrodealkylation, hydrocracking, and hydrodesulfurization, and in oxyhydrogen torches. Liquid hydrogen is employed as a rocket fuel.
The hydrogen fuel cell is a developing technology that will allow much electrical power to be obtained using a hydrogen gas.
Preparation of hydrogenHydrogen can be prepared, industrially and in the laboratory, by a variety of methods, including:
Ortho- and para- forms of hydrogenQuite apart from isotopes, it has been shown that under ordinary conditions hydrogen gas is a mixture of two kinds of molecules, known as orthohydrogen and parahydrogen, which differ from one another by the spins of the protons in their nuclei. In orthohydrogen the protons have opposite spin; in parahydrogen they have the same spin. 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.
Hydrogen in spaceHydrogen makes up the bulk of most stars and gas giant planets. In space, it may exist in atomic (see H I region), ionized (see H II region), or molecular form (see molecular cloud). The presence of atomic hydrogen in space can be mapped by observations of the 21-centimeter line.
Related category INORGANIC CHEMISTRY
Source: Los Alamos National Laboratory
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