Hydrogen is a chemical element; it has symbol H and atomic number 1. It is the lightest element and, at standard conditions, is a gas of diatomic molecules with the formula H2, sometimes called dihydrogen, hydrogen gas, molecular hydrogen, or simply hydrogen. It is colorless, odorless, non-toxic, and highly combustible. Constituting about 75% of all normal matter, hydrogen is the most abundant chemical element in the universe. Stars, including the Sun, mainly consist of hydrogen in a plasma state, while on Earth, hydrogen is found in water, organic compounds, as dihydrogen, and in other molecular forms. The most common isotope of hydrogen (protium, 1H) consists of one proton, one electron, and no neutrons.
In the early universe, the formation of hydrogen's protons occurred in the first second after the Big Bang; neutral hydrogen atoms only formed about 370,000 years later during the recombination epoch as the universe expanded and plasma had cooled enough for electrons to remain bound to protons. Hydrogen gas was first produced artificially in the early 16th century by the reaction of acids with metals. Henry Cavendish, in 1766–81, identified hydrogen gas as a distinct substance and discovered its property of producing water when burned; hence its name means "water-former" in Greek. Understanding the colors of light absorbed and emitted by hydrogen was a crucial part of developing quantum mechanics.
Hydrogen, typically nonmetallic except under extreme pressure, readily forms covalent bonds with most nonmetals, contributing to the formation of compounds like water and various organic substances. Its role is crucial in acid-base reactions, which mainly involve proton exchange among soluble molecules. In ionic compounds, hydrogen can take the form of either a negatively charged anion, where it is known as hydride, or as a positively charged cation, H+, called a proton. Although tightly bonded to water molecules, protons strongly affect the behavior of aqueous solutions, as reflected in the importance of pH. Hydride on the other hand, is rarely observed because it tends to deprotonate solvents, yielding H2.
Industrial hydrogen production occurs through steam reforming of natural gas. The more familiar electrolysis of water is uncommon because it is energy-intensive, i.e. expensive. Its main industrial uses include fossil fuel processing, such as hydrocracking and hydrodesulfurization. Ammonia production also is a major consumer of hydrogen. Fuel cells for electricity generation from hydrogen is rapidly emerging. |
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Homo sapiens
(NCBI:txid9606)
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DOI
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antioxidant
A substance that opposes oxidation or inhibits reactions brought about by dioxygen or peroxides.
electron donor
A molecular entity that can transfer an electron to another molecular entity.
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human metabolite
Any mammalian metabolite produced during a metabolic reaction in humans (Homo sapiens).
food packaging gas
A food additive that is a (generally inert) gas which is used to envelop foodstuffs during packing and so protect them from unwanted chemical reactions such as food spoilage or oxidation during subsequent transport and storage. The term includes propellant gases, used to expel foods from a container.
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fuel
An energy-rich substance that can be transformed with release of usable energy.
food packaging gas
A food additive that is a (generally inert) gas which is used to envelop foodstuffs during packing and so protect them from unwanted chemical reactions such as food spoilage or oxidation during subsequent transport and storage. The term includes propellant gases, used to expel foods from a container.
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View more via ChEBI Ontology
dihydrogen
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ChEBI
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E 949
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ChEBI
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E-949
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ChEBI
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E949
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ChEBI
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H2
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KEGG COMPOUND
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H2
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IUPAC
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H2
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UniProt
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Hydrogen
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KEGG COMPOUND
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molecular hydrogen
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ChEBI
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1333-74-0
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CAS Registry Number
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KEGG COMPOUND
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1333-74-0
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CAS Registry Number
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ChemIDplus
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1333-74-0
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CAS Registry Number
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NIST Chemistry WebBook
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3
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Gmelin Registry Number
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Gmelin
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3587189
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Reaxys Registry Number
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Reaxys
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15303745
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PubMed citation
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Europe PMC
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16517646
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PubMed citation
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Europe PMC
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18706888
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PubMed citation
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Europe PMC
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19905000
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PubMed citation
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Europe PMC
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19908827
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PubMed citation
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Europe PMC
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20568549
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PubMed citation
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Europe PMC
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24171421
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PubMed citation
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Europe PMC
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