Oxygen

Oxygen, ₀₀O

Liquid oxygen boiling
Oxygen
Allotropes	O2, O3 (ozone) and more (see Allotropes of oxygen)
Appearance	(O2) gas: colourless liquid and solid: pale blue
Standard atomic weight Ar°(O)
	[15.99903, 15.99977][1]
Abundance
in the Earth's crust	46%
in the oceans	86%
in the solar system	1%
Oxygen in the periodic table
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 Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver 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 Gold Mercury (element) Thallium Lead 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 Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson – ↑ O ↓ S nitrogen ← oxygen → fluorine
Group	group 16 (chalcogens)
Period	period 2
Block	p-block
Electron configuration	[He] 2s2 2p4
Electrons per shell	2, 6
Physical properties
Phase at STP	gas (O2)
Melting point	54.36 K ​(−218.79 °C, ​−361.82 °F)
Boiling point	90.188 K ​(−182.962 °C, ​−297.332 °F)
Density (at STP)	1.429 g/L
when liquid (at b.p.)	1.141 g/cm3
Triple point	54.361 K, ​0.1463 kPa
Critical point	154.581 K, 5.043 MPa
Heat of fusion	(O2) 0.444 kJ/mol
Heat of vaporization	(O2) 6.82 kJ/mol
Molar heat capacity	(O2) 29.378 J/(mol·K)
Vapor pressure 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
Ionization 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 of oxygen
Other properties
Natural occurrence	primordial
Crystal structure	​cubic
Speed of sound	330 m/s (gas, at 27 °C)
Thermal conductivity	26.58×10−3  W/(m⋅K)
Magnetic ordering	paramagnetic
Molar magnetic susceptibility	+3449.0·10−6 cm3/mol (293 K)[2]
CAS Number	7782-44-7
History
Discovery	Carl Wilhelm Scheele (1771)
Named by	Antoine Lavoisier (1777)
Isotopes of oxygen v e
Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 15O 0% (extinct) Preview warning: Infobox O isotopes: Abundance percentage not recognised "na=0% (extinct)" cat#% 122.266 s β+100% 15N 16O 99.8% stable 17O 0.0380% stable 18O 0.205% stable
Category: Oxygen view talk edit | references

Oxygen is a chemical element. It has the symbol O and atomic number 8. It is the third most common element in the universe, after hydrogen and helium.

Oxygen is more than a fifth of the Earth's atmosphere by volume. In the air, two oxygen atoms usually join to make dioxygen (O
₂), a colourless gas. This gas is often just called oxygen. It has no taste or smell. It is pale blue when it is liquid or solid.

Oxygen is part of the chalcogen group on the periodic table. It is a very reactive nonmetal. It makes oxides and other compounds with many elements. The oxygen in these oxides and in other compounds (mostly silicate minerals, and calcium carbonate in limestone) makes up nearly half of the Earth's crust, by mass.

Most living things use oxygen in respiration. Many molecules in living things have oxygen in them, such as proteins, nucleic acids, carbohydrates and fats. Oxygen is a part of water, which all known life needs to live. Algae, cyanobacteria and plants make the Earth's oxygen gas by photosynthesis. They use the Sun's light to get hydrogen from water, giving off oxygen.

At the top of the Earth's atmosphere is ozone (O
₃), in the ozone layer. It absorbs ultraviolet radiation, which means less radiation reaches ground level.

Oxygen gas is used for making steel, plastics and textiles. It also has medical uses and is used for breathing when there is no good air (by divers and firefighters, for example), and for welding. Liquid oxygen and oxygen-rich compounds can be used as a rocket propellant.

1. ↑ "Standard Atomic Weights: Oxygen". CIAAW. 2009.
2. ↑ Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.