hydrogen (H) [hi´dro-jen]
a chemical element, atomic number 1, atomic weight 1.00797. (See Appendix 6.) It exists as the mass 1 isotope (protium, or light or ordinary hydrogen), mass 2 isotope (deuterium, heavy hydrogen), and mass 3 isotope (tritium).
an extremely poisonous colorless liquid or gas, HCN, a decomposition product of various naturally occurring glycosides and a common cause of cyanide poisoning
. Inhalation of the gas can cause death within a minute. Called also hydrocyanic acid
hydrogen ion concentration
the degree of concentration of hydrogen ions (the acid element) in a solution. Its symbol is pH, and it expresses the degree to which a solution is acidic or alkaline. The pH range extends from 0 to 14, pH 7 being neutral, a pH of less than 7 indicating acidity, and one above 7 indicating alkalinity. See also acid-base balance
hydrogen peroxide H2O2, an antiseptic with a mildly antibacterial action. A 3 per cent solution foams on touching skin or mucous membrane and appears to have a mechanical cleansing action.
hydrogen sulfide H2S, a poisonous gas with an offensive smell, released from decaying organic material, natural gas, petroleum, and sulfur deposits, and sometimes used as a chemical reagent.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
hydrogen (hi'dro-jen) [ hydro- + -gen] H
A colorless, odorless, tasteless, gaseous chemical element, possessing one valence electron, atomic weight (mass) 1.0079, specific gravity 0.069, atomic number 1. A liter of the gas at sea level and at 0°C weighs 0.08988 g. There are three isotopes of hydrogen (protium, deuterium, and tritium), having atomic weights of approx. 1, 2, and 3, respectively.
Hydrogen is present in the sun and stars. Even though it is the most abundant element in the known universe, its concentration in the earth's atmosphere is only 0.00005%. Hydrogen occurs in its free state (in natural gases and volcanic eruptions) only in minute quantities. It occurs principally on the earth as water (hydrogen oxide, H2O) and is a constituent of all hydrocarbons. Hydrogen is present in all acids and in ionic form is responsible for the properties characteristic of acids. Hydrogen is present in nearly all organic compounds and is a component of all carbohydrates, proteins, and fats.
It is highly flammable and used in the oxyhydrogen flame in welding, in hydrogenation of oils for solidifying purposes, as a reducing agent, and in many syntheses.
hydrogen cyanideHydrocyanic acid.
hydrogen dioxideHydrogen peroxide.
hydrogen iodideHydriodic acid.
, a colorless syrupy liquid with an irritating odor and acrid taste. It decomposes readily, liberating oxygen. Because light is particularly effective in decomposing H2
, it must be stored in tightly sealed glass jars in a dark place. Synonym: hydrogen dioxide
It is used as a commercial bleaching agent; as an oxidizing and reducing agent; and, in a 3% aqueous solution, as a mild antiseptic, germicide, and cleansing agent.
S, a poisonous, flammable, colorless compound with a characteristic odor of rotten eggs. Synonym: sulfurated hydrogen
Synonym: hydrosulfuric acid
sulfurated hydrogenHydrogen sulfide
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