1. A gaseous element, atomic no. 8, atomic wt. 15.9994 on the basis of 12C = 12.0000; an abundant and widely distributed chemical element, which combines with most of the other elements to form oxides and is essential to animal and plant life. 2. The molecular form of o., O2. 3. A medicinal gas that contains not less than 99.0%, by volume, of O2. [G. oxys, sharp, acid and genes, forming]
- heavy o. SYN: o.-18.
- hyperbaric o., high pressure o. o. at a pressure greater than 1 atm. SEE ALSO: hyperbaric oxygenation.
- singlet o. an excited or higher-energy form of o. characterized by the spin of a pair of electrons in opposite directions, whereas electron spin is unidirectional in normal molecular o. Because of its great reactivity, singlet o. is a probable intermediate in most photo-oxidation reactions. Although it exists for no more than 0.1 second, it may react with atmospheric pollutants to foster smog formation and may have harmful biologic effects.
- triplet o. the normal unexcited state of O2 in the atmosphere, in which the unpaired pair of electrons are so displaced that their magnetic fields are oriented in the same direction, resulting in paramagnetism; each of the heat-generated spectral lines of such o. can be split by a magnetic field into a triplet. Cf.:singlet o..

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ox·y·gen 'äk-si-jən n a colorless tasteless odorless gaseous element that constitutes 21 percent of the atmosphere and is found in water, in most rocks and minerals, and in numerous organic compounds, that is capable of combining with all elements except the inert gases, that is active in physiological processes, and that is involved esp. in combustion processes symbol O see ELEMENT (table)
ox·y·gen·ic .äk-si-'jen-ik adj

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an odourless colourless gas that makes up one-fifth of the atmosphere. Oxygen is essential to most forms of life in that it combines chemically with glucose (or some other fuel) to provide energy for metabolic processes. It is absorbed into the blood from air breathed into the lungs. Oxygen is administered therapeutically in various conditions in which the tissues are unable to obtain an adequate supply through the lungs (see oxygenator, tent). Symbol: O.

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ox·y·gen (O) (okґsĭ-jən) [Gr. oxys sour + gennan to produce] a gaseous element existing free in the air and in combination in most nonelementary solids, liquids, and gases; atomic number, 8; atomic weight, 15.999. There are three naturally occurring isotopes, with atomic weights of 16, 17, and 18 (heavy oxygen). Oxygen constitutes 20 per cent by weight of the atmospheric air; it is the essential agent in the respiration of plants and animals and, although nonflammable, is necessary to support combustion. It forms the characteristic constituent of ternary acids. It is administered by inhalation in some pulmonary and cardiac disorders.

Medical dictionary. 2011.

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