Oxygen

Oxygen is a chemical element wi symbol O an atomic nummer 8. It is a member o the chalcogen group on the periodic cairt an is a heichly reactive nonmetal an oxidisin agent that readily forms oxides wi maist elements as well as ither compoonds. Bi mass, oxygen is the third-maist abundant element in the universe, efter hydrogen an helium. At staundart temperatur an pressur, twa atoms o the element bind tae form dioxygen, a colourless an odourless diatomic gas wi the formula O
₂. This is an important pairt o the atmosphere an diatomic oxygen gas constitutes 20.8% o the Yird's atmosphere. Addeetionally, as oxides the element maks up awmaist hauf o the Yird's crust.

Oxygen, ₈O

Liquid oxygen bylin
Oxygen
Appearance	gas: colourless liquid: pale blue
Standard atomic weight Ar, std(O)	[7001159990300000000♠15.99903, 7001159997700000000♠15.99977] conventional: 7001159990000000000♠15.999
Mass number	O:
Oxygen in the periodic cairt
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Airn Cobalt Nickel Capper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Siller (element) Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gowd Mercur (element) Thallium Leid (element) Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Ununtrium Flerovium Ununpentium Livermorium Ununseptium Ununoctium – ↑ O ↓ S nitrogen ← oxygen → fluorine
Atomic nummer (Z)	8
Group	group 16 (chalcogens)
Period	period 2
Block	p-block
Element category	Reactive nonmetal
Electron confeeguration	[He] 2s2 2p4
Electrons per shell	2, 6
Pheesical properties
Phase at STP	gas
Meltin pynt	54.36 K ​(−218.79 °C, ​−361.82 °F)
Bylin pynt	90.188 K ​(−182.962 °C, ​−297.332 °F)
Density (at STP)	1.429 g/L
whan liquid (at b.p.)	1.141 g/cm3
Treeple pynt	54.361 K, ​0.1463 kPa
Creetical pynt	154.581 K, 5.043 MPa
Heat o fusion	(O2) 0.444 kJ/mol
Heat o vapourisation	(O2) 6.82 kJ/mol
Molar heat capacity	(O2) 29.378 J/(mol·K)
Vapour pressur P (Pa) 1 10 100 1 k 10 k 100 k at T (K)       61 73 90
Atomic properties
Oxidation states	−2, −1, 0, +1, +2
Electronegativity	Pauling scale: 3.44
Ionisation energies	1st: 1313.9 kJ/mol 2nd: 3388.3 kJ/mol 3rd: 5300.5 kJ/mol (more)
Covalent radius	66±2 pm
Van der Waals radius	152 pm
Spectral lines o oxygen
Ither properties
Naitural occurrence	O: Primordial
Creestal structur	​cubic
Speed o soond	330 m/s (gas, at 27 °C)
Thermal conductivity	26.58×10−3  W/(m·K)
Magnetic orderin	paramagnetic
Magnetic susceptibility	+3449.0·10−6 cm3/mol (293 K)
CAS Nummer	7782-44-7
History
Diskivery	Carl Wilhelm Scheele (1771)
Named by	Antoine Lavoisier (1777)
Main isotopes o oxygen
Iso­tope Abun­dance Hauf-life (t1/2) Decay mode Pro­duct 16O 99.76% stable 17O 0.04% stable 18O 0.20% stable

Dioxygen is uised in cellular respiration an mony major classes o organic molecules in livin organisms conteen oxygen, sic as proteins, nucleic acids, carbohydrates, an fats, as dae the major consteetuent inorganic compoonds o ainimal shells, teeth, an bane. Maist o the mass o livin organisms is oxygen as a component o watter, the major constituent o lifeforms. Conversely, oxygen is continuously replenished bi photosynthesis, which uises the energy o sunlicht tae produce oxygen frae watter an carbon dioxide. Oxygen is ower chemically reactive tae remeen a free element in air withoot bein continuously replenished bi the photosynthetic action o livin organisms. Anither form (allotrope) o oxygen, ozone (O
₃), strangly absorbs ultraviolet UVB radiation an the heich-altitude ozone layer helps pertect the biosphere frae ultraviolet radiation. But ozone is a pollutant near the surface whaur it is a bi-product o smog. At law yird orbit altitudes, sufficient atomic oxygen is present tae cause corrosion o spacecraft.

Oxygen wis discovered independently bi Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, an Joseph Priestley in Wiltshire, in 1774, but Priestley is eften gien priority acause his wark wis published first. The name oxygen wis coined in 1777 bi Antoine Lavoisier, whase experiments wi oxygen helped tae discredit the then-popular phlogiston theory o combustion an corrosion. Its name derives frae the Greek roots ὀξύς oxys, "acid", leeterally "sharp", referrin tae the soor taste o acids an -γενής -genes, "producer", leeterally "begetter", acause at the time o namin, it wis mistakenly thocht that aw acids required oxygen in thair composeetion.

Common uise o oxygen includes residential heatin, internal combustion ingines, production o steel, plastics an textiles, brazin, waldin an cuttin o steels an ither metals, rocket propellant, oxygen therapy, an life support seestems in aircraft, submarines, spaceflicht an divin.