Oxygen (pronounced /??ks?d??n/ , from the Greek roots ???? (oxys) (acid, literally "sharp," from the taste of acids) and -????? (-gen?s) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O . more

Oxygen (pronounced /??ks?d??n/ , from the Greek roots ???? (oxys) (acid, literally "sharp," from the taste of acids) and -????? (-gen?s) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O . It is a member of the chalcogen group on the periodic table , and is a highly reactive nonmetallic period 2 element that readily forms compounds (notably oxides ) with almost all other elements. At standard temperature and pressure two atoms of the element bind to form dioxygen, a colorless, odorless, tasteless diatomic gas with the formula O 2 . Oxygen is the third most abundant element in the universe by mass after hydrogen and helium [ 1 ] and the most abundant element by mass in the Earth's crust . [ 2 ] Diatomic oxygen gas constitutes 20.9% of the volume of air . [ 3 ] less