氧

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氧(oxygen)

周期表VIa族非金属化学元素。化学符号O，原子序数8。无色、无臭、无味的气体，为地壳中含量最多的元素，它的最重要的化合物是水。氧在大气中占21%，在地壳中占46.6%。溶解的氧对鱼类和其他海洋生物的呼吸非常重要。地面和下层大气的氧气，几乎都由双原子分子O2组成。动物和低级植物呼吸时，从大气吸入氧气，呼出二氧化碳。高级（即绿色）植物则在阳光下通过光合作用吸收二氧化碳并放出氧气。在空气的主要成分中，氧的沸点最高，不易挥发。在炼钢和其他冶金过程中，在生产乙炔和甲醇等控制氧化的化学制品的化学工业中，工业氧或富氧空气已逐渐取代了普通的空气。氧在医学上用於氧气幕、人工呼吸器和早产婴儿保育箱。氧是航天器、水中呼吸器和高压室的部分气体混合物。液态氧还用作火箭发动机燃料。氧的原子价是2，能形成各种各样的共价化合物，其中包括水、二氧化硫和二氧化碳等非金属氧化物，醇、醛、羧酸等有机化合物。

English version：

oxygen

Gaseous chemical element, chemical symbol O, atomic number 8. It constitutes 21% (by volume) of air and over 46% (by weight) of the earth's crust, where it is the most plentiful element. It is a colorless, odorless, tasteless gas, occurring as the diatomic molecule O2. In respiration, it is taken up by animals and some bacteria (and by plants in the dark), which give off carbon dioxide (CO2). In photosynthesis, green plants assimilate carbon dioxide in the presence of sunlight and give off oxygen. The small amount of oxygen that dissolves in water is essential for the respiration of fish and other aquatic life. Oxygen takes part in combustion and in corrosion but does not itself burn. It has valence 2 in compounds; the most important is water. It forms oxides and is part of many other molecules and functional groups, including nitrate, sulfate, phosphate, and carbonate; alcohols, aldehydes, carboxylic acids, and ketones; and peroxides. Obtained for industrial use by distillation of liquefied air, oxygen is used in steelmaking and other metallurgical processes and in the chemical industry. Medical uses include respiratory therapy, incubators, and inhaled anesthetics. Oxygen is part of all gas mixtures for spacecraft, scuba divers, workers in closed environments, or hyperbaric chambers. It is also the oxidizer in rocket engines and in water and waste treatment processes.