hydrogen

American  

[hahy-druh-juhn] / ˈhaɪ drə dʒən /

noun

1. a colorless, odorless, flammable gas that combines chemically with oxygen to form water: the lightest of the known elements. H; 1.00797; 1; density: 0.0899 grams/liter at 0°C and 760 millimeters pressure.

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hydrogen British  

/ ˈhaɪdrɪdʒən /

noun

1. 1. a flammable colourless gas that is the lightest and most abundant element in the universe. It occurs mainly in water and in most organic compounds and is used in the production of ammonia and other chemicals, in the hydrogenation of fats and oils, and in welding. Symbol: H; atomic no: 1; atomic wt: 1.00794; valency: 1; density: 0.08988 kg/m³; melting pt: –259.34°C; boiling pt: –252.87°C See also deuterium tritium

   2. ( as modifier )

      hydrogen bomb

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hydrogen Scientific  

/ hī′drə-jən /

1. The lightest and most abundant element in the universe, normally consisting of one proton and one electron. It occurs in water in combination with oxygen, in most organic compounds, and in small amounts in the atmosphere as a gaseous mixture of its three isotopes (protium, deuterium, and tritium) in the colorless, odorless compound H ₂. Hydrogen atoms are relatively electropositive and form hydrogen bonds with electronegative atoms. In the Sun and other stars, the conversion of hydrogen into helium by nuclear fusion produces heat and light. Hydrogen is used to make rocket fuel, synthetic ammonia, and methanol, to hydrogenate fats and oils, and to refine petroleum. The development of physical theories of electron orbitals in hydrogen was important in the development of quantum mechanics. Atomic number 1; atomic weight 1.00794; melting point −259.14°C; boiling point −252.8°C; density at 0°C 0.08987 gram per liter; valence 1.

2. See Periodic Table See Note at oxygen

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Etymology

Origin of hydrogen

First recorded in 1785–95; from the French word hydrogène; hydro- ¹, -gen

Compare meaning

How does hydrogen compare to similar and commonly confused words? Explore the most common comparisons:

• hydrogen vs. atomic bomb
• deuterium vs. hydrogen

Example Sentences

Among the cuts was a $1.2 billion federal grant for California’s hydrogen hub, the Alliance for Renewable Clean Hydrogen Energy Systems, or ARCHES.

From Los Angeles Times

Filled with hydrogen, they were used to reconnoiter enemy positions, their passengers hand-sketching battlefield maps.

From The Wall Street Journal

Southern California Gas Co. wants to use Orange Cove to test blending hydrogen with natural gas in its pipeline network.

From Los Angeles Times

Water is made of hydrogen and oxygen, and some of these atoms naturally exist in slightly heavier forms called isotopes.

From Science Daily

Stars shine because nuclear fusion in their cores converts hydrogen into helium, creating outward pressure that counteracts gravity.

From Science Daily