hydrogen

hy·dro·gen

noun \ˈhī-drə-jən, -dər-\

Definition of HYDROGEN

: a nonmetallic element that is the simplest and lightest of the elements, is normally a colorless odorless highly flammable diatomic gas, and is used especially in synthesis — see element table — compare deuterium, tritium

— hy·drog·e·nous \hī-ˈdrä-jə-nəs\ adjective

Origin of HYDROGEN

French hydrogène, from hydr- + -gène -gen; from the fact that water is generated by its combustion

First Known Use: 1788

hy·dro·gen

noun \ˈhī-drə-jən\   (Medical Dictionary)

Medical Definition of HYDROGEN

: a nonmetallic element that is the simplest and lightest of the elements and that is normally a colorless odorless highly flammable diatomic gas—symbol H; see deuterium, tritium; element table

—hy·drog·e·nous \hī-ˈdräj-ə-nəs\ adjective

hydrogen

noun    (Concise Encyclopedia)

Lightest chemical element, chemical symbol H, atomic number 1. A colourless, odourless, tasteless, flammable gas, it occurs as the diatomic molecule H. Its atom consists of one proton (the nucleus) and one electron; the isotopes deuterium and tritium have an additional one and two nuclear neutrons, respectively. Though only the ninth most abundant element on Earth, it represents about 75% of all matter in the universe. Hydrogen was formerly used to fill airships; nonflammable helium has replaced it. It is used to synthesize ammonia, ethanol, aniline, and methanol; to treat petroleum fuels; as a reducing agent (see reduction) and to supply a reducing atmosphere; to make hydrogen chloride (see hydrochloric acid) and hydrogen bromide; and in hydrogenation (e.g., of fats). Liquid hydrogen (boiling point 423 °F [252.8 °C]) is used in scientific and commercial applications to produce extremely low temperatures and as a rocket propellant and a fuel for fuel cells. Combustion of hydrogen with oxygen gives water as the sole product. The properties of most acids, especially in water solutions, arise from the hydrogen ion (H⁺, also referred to as the hydronium ion, HO⁺, the form in which H⁺ is found in a water environment). See also hydride; hydrocarbon.