氧Oxygen

氧的电负性仅次于氟，通常获得两个电子形成 O²⁻ 或两个共价键。O₂ 分子的分子轨道排布中有两个未成对电子占据 π* 轨道，所以 O₂ 是顺磁性的，液氧会被磁铁吸引，这是分子轨道理论优于路易斯结构的经典例证。O₂ 的键级为 2，键长 121 pm。

Oxygen is second only to fluorine in electronegativity and usually gains two electrons to form O²⁻ or makes two covalent bonds. In O₂ two unpaired electrons occupy π* orbitals, so the molecule is paramagnetic and liquid oxygen is attracted by a magnet, the classic case where molecular orbital theory beats a Lewis structure. The bond order is 2 and the bond length 121 pm.

1771–1772 年舍勒加热氧化汞等物质得到“火空气”，但发表较晚；1774 年普里斯特利加热氧化汞独立制得“脱燃素空气”。拉瓦锡通过定量实验指出燃烧是物质与这种气体的化合，推翻了燃素说，并于 1777 年命名为 oxygène（“成酸者”，他误以为所有酸都含氧）。

In 1771–72 Scheele obtained 'fire air' by heating mercury oxide and other substances but published late; in 1774 Priestley independently made 'dephlogisticated air' from mercury oxide. Lavoisier's quantitative experiments showed that combustion is combination with this gas, overthrowing the phlogiston theory, and in 1777 he named it oxygène, acid-former, wrongly believing all acids contain oxygen.

氧有 O₂ 和臭氧 O₃ 两种主要同素异形体，平流层中的臭氧层吸收紫外线。工业上通过空气深冷分离或变压吸附制氧，用于炼钢（转炉吹氧）、医疗、焊接切割、化工氧化和火箭推进剂（液氧）。

Oxygen's main allotropes are O₂ and ozone, O₃; the stratospheric ozone layer absorbs ultraviolet light. Industry produces oxygen by cryogenic air separation or pressure-swing adsorption for steelmaking (oxygen blowing), medicine, welding and cutting, chemical oxidations and rocket propellant (liquid oxygen).