Oxygen

Symbol: O
Atomic number: 8
Category: nonmetals
Group: 16
Period: 2
Block: p
Atomic weight: 15.9994 g/mol
Electrons per shell: 2, 6
CAS number: 7782-44-7
Phase: gas
Density: 1.429 g/l (0 °C, 101.325 kPa)
Melting point: 54.36 K (-218.79 °C, -361.82 °F)
Boiling point: 90.20 K (-182.95 °C, -297.31 °F)
Crystal structure: cubic
Oxidation states: 2, 1, -1, -2
Electronegativity: 3.44 (Pauling scale)
Name's origin: oxygenium
Name's meaning: the Greek words 'oxys' and 'genes' which mean 'acid producer'
Facts:
- 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, and tasteless gas
- is the third most abundant element in the universe by mass after hydrogen and helium
- diatomic oxygen gas constitutes 20.9% of the volume of air
- all major classes of structural molecules in living organisms, such as proteins, carbohydrates, and fats, contain oxygen, as do the major inorganic compounds that comprise animal shells, teeth, and bone
- another form (allotrope) of oxygen, ozone (O₃), helps protect the biosphere from ultraviolet radiation with the high-altitude ozone layer, but is a pollutant near the surface where it is a by-product of smog
- is produced industrially by fractional distillation of liquefied air, use of zeolites to remove carbon dioxide and nitrogen from air, electrolysis of water and other means
- is used in the production of steel, plastics and textiles; rocket life support in aircraft, submarines, spaceflight, and diving
- highly concentrated sources of oxygen promote rapid combustion, yet the oxygen itself is not the fuel, but the oxidant