Hydrogen

Hydrogen is a chemical element; it has the symbolH and atomic number1. It is the lightest and most abundant chemical element in the universe, constituting about 75% of all normal matter. Under standard conditions, hydrogen is a gas of diatomic molecules with the formula, called dihydrogen, or sometimes hydrogen gas, molecular hydrogen, or simply hydrogen. Dihydrogen is colorless, odorless, non-toxic, and highly combustible. Stars, including the Sun, mainly consist of hydrogen in a plasma state, while on Earth, hydrogen is found as the gas (dihydrogen) and in molecules, such as in water and org

thumb| Steps in the hydrogenation of a C=C double bond at a catalyst surface, for example Ni or Pt : (1) The reactants are Adsorption|adsorbed on the catalyst surface and H2 dissociates. (2) An H atom bonds to one C atom. The other C atom is still attached to the surface. (3) A second C atom bonds to an H atom. The molecule leaves the surface.

thumb|right|upright=1.2|Antihydrogen consists of an antiproton and a [[positron]] thumb|right|upright=1.2|Simplified model of an antihydrogen atom in ground state

hydrogen with different numbers of neutrons

atom of element hydrogen

phase of hydrogen

liquid state of the element hydrogen

In chemistry, dehydrogenation is a chemical reaction that involves the removal of hydrogen, usually from an organic molecule. It is the reverse of hydrogenation. Dehydrogenation is important, both as a useful reaction and a serious problem. At its simplest, it is a useful way of converting alkanes, which are relatively inert and thus low-valued, to olefins, which are reactive and thus more valuable. Alkenes are precursors to aldehydes (), alcohols (), polymers, and aromatics. As a problematic reaction, the fouling and inactivation of many catalysts arises via coking, which is the dehydrogenati

In chemistry, the hydron, informally called proton, is the cationic form of atomic hydrogen, represented with the symbol . The general term "hydron", endorsed by IUPAC, encompasses cations of hydrogen regardless of isotope: thus it refers collectively to protons (H) for the protium isotope, deuterons (H or D) for the deuterium isotope, and tritons (H or T) for the tritium isotope.

important atomic emission spectra

spectral line of hydrogen state transitions

methanation process of carbon dioxide with hydrogen

A planet with a helium-dominated atmosphere

isotopic compound composed of one protium atom and one deuterium atom

reduction in ductility of a metal exposed to hydrogen

thumb|Microbial hydrogen production. Biohydrogen is H2 that is produced biologically. Interest is high in this technology because H2 is a clean fuel and can be readily produced from certain kinds of biomass, including biological waste. Furthermore some photosynthetic microorganisms are capable of producing H2 directly from water splitting using light as energy source.

alloy of aluminium, copper and zinc

Hydrogenolysis is a chemical reaction whereby a carbon–carbon or carbon–heteroatom single bond is cleaved or undergoes lysis (breakdown) by hydrogen. The heteroatom may vary, but it usually is oxygen, nitrogen, or sulfur. A related reaction is hydrogenation, where hydrogen is added to the molecule, without cleaving bonds. Usually hydrogenolysis is conducted catalytically using hydrogen gas.

forms elemental carbon from CO2 and hydrogen using a metallic catalyst

Aromatization is a chemical reaction in which an aromatic system is formed from a single nonaromatic precursor. Typically aromatization is achieved by dehydrogenation of existing cyclic compounds, illustrated by the conversion of cyclohexane into benzene. Aromatization includes the formation of heterocyclic systems. center|422px|thumb|The conversion of methylcyclohexane to [[toluene is a classic aromatization reaction. This platinum (Pt)-catalyzed process is practiced on scale in the production of gasoline from petroleum.]]

procedures for safe production, handling and use of hydrogen

unstable allotrope of hydrogen

hydrogen that is formed by natural process

hydrogen exchange between the living and non-living world

term in biology

spin states of hydrogen

Belgium-based industry group

outdated concept for reactive hydrogen

class of chemical compounds