Oxygen (O₂) (beginner)

Oxygen (O₂) (beginner)

A colourless, odourless gas, an important component of the atmosphere, indispensable to sustain terrestrial life.



oxygen, oxygen molecule, homonuclear molecule, condition for life, respiration, air, covalent bond, double bond, sigma bond, pi bond, nonpolar, oxide, exothermic, photosynthesis, inorganic chemistry, general chemistry, chemistry

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Oxygen O₂


Molar mass: 31.999 g/mol

Melting point: -218.8 °C

Boiling point: -182.9 °C


Oxygen is a colourless, odourless gas at room temperature. It dissolves weakly in water. Under normal circumstances, molecular oxygen is only lightly reactive, but at higher temperatures it reacts with all the elements except for the halogens and noble gases. Its reactions are exothermic and produce oxides. Oxygen feeds combustion; living organisms need it for their physiological processes.

Occurrence and production

Oxygen is the most abundant element on Earth; it constitutes 50.5% of the Earth´s crust by mass and 21% of the air by volume. Plants release oxygen into the atmosphere during photosynthesis. In laboratories, oxygen is produced by heating potassium permanganate, while it is manufactured in industrial quantities during the fractional distillation of liquid air at about -183 °C.


In industry, oxygen is used in the production of high temperature flames, in the direct oxidation of titanium dioxide and ethylene, and in the production of syngas. Large volumes of oxygen are used in iron and steel making. In medicine, it is used as a breathing gas.



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