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O symbol, atomic number 8, amu 15.9994, the external electronic arrangement 2S22p4, at the second cycle of group A VI. Covalent atomic radius of 66 picometer, ionic radius O2-132 picometer, 1314kJ/mol the first ionization energy, electricity negative 3.5. There are two elements of oxygen with allotropism oxygen, ozone O3 and O2. Molecular oxygen is obvious paramagnetic, it is because of O2 molecules is a σ keys, and two π three electronic keys consist of two three electronic keys have two π 16.27 electronic, O2 is the paramagnetic. Oxygen in normal conditions for the colorless, odorless, tasteless gas density of 1.429 g / l (gas), 1.149g/cm3 (liquid), 1.426g/cm3 (solid). -218.4 ° C melting point, boiling point -182.962 ° C. Major oxidation at -2, perfluorocarbons +2 oxygen for the peroxide to -1. Pale blue liquid oxygen, oxygen solid blue crystal. Water-soluble in the water solubility of 4.89 ml / 100 ml of water (0 ° C). As larger dissociation (498.1kJ/mol), the room temperature oxygen chemical nature is not lively, high temperature and chemical properties of very lively, with most of the elements combine to form one or more oxides or peroxide. It is important oxidative the oxidizer. Pure oxygen is used extensively for metal smelting, refining, welding, cutting and surface treatment processes. The chemical industry used oxygen enhanced the production process. Liquid oxygen used refrigerant, as well as high-energy fuel oxidizer. It sawdust, coal is a mixture of liquid oxygen explosives. Pure oxygen is also used aviation, diving and medical China. Natural presence of oxygen from the 16O (99.759%), 170 (0.037%), 18O (0.204%) three isotopic composition. The earth's abundance of 49.5%, accounting for the first one. Most water, oxides, silicates form. Dry air volume containing 20.946% oxygen. In 1773 Sweden Scheler nitrate decomposition and the use of concentrated sulfuric acid with manganese dioxide prepared by the reaction of oxygen. In 1774 the British Pulishiteli heating mercury oxide in oxygen system. Industrial use liquids fractionation system in the air, use a water electrolysis system more pure oxygen. Laboratory commonly used potassium chlorate and manganese dioxide (catalyst) from hybrid heating system.
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