什麼是氧

週期表VIa族非金屬化學元素。化學符號O，原子序數8。無色、無臭、無味的氣體，為地殼中含量最多的元素，它的最重要的化合物是水。氧在大氣中佔21%，在地殼中佔46.6%。溶解的氧對魚類和其他海洋生物的呼吸非常重要。地面和下層大氣的氧氣，幾乎都由雙原子分子O2組成。動物和低階植物呼吸時，從大氣吸入氧氣，撥出二氧化碳。高階（即綠色）植物則在陽光下通過光合作用吸收二氧化碳並放出氧氣。在空氣的主要成分中，氧的沸點最高，不易揮發。在鍊鋼和其他冶金過程中，在生產乙炔和甲醇等控制氧化的化學制品的化學工業中，工業氧或富氧空氣已逐漸取代了普通的空氣。氧在醫學上用於氧氣幕、人工呼吸器和早產嬰兒保育箱。氧是航天器、水中呼吸器和高壓室的部分氣體混合物。液態氧還用作火箭發動機燃料。氧的原子價是2，能形成各種各樣的共價化合物，其中包括水、二氧化硫和二氧化碳等非金屬氧化物，醇、醛、羧酸等有機化合物。

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.