Oxygen From Wikipedia, the free encyclopedia This article is about the chemical element and its most stable form, O 2 or dioxygen. For other forms of this element, see Allotropes of oxygen. For other uses, see Oxygen (disambiguation) and O2 (disambiguation). Page semi-protected Oxygen 8O ↑ O ↓ S nitrogen ← oxygen → fluorine Oxygen in the periodic table Appearance colorless gas; pale blue liquid. Oxygen bubbles rise in this photo of liquid oxygen. A glass bottle half-filled with a bluish bubbling liquid Spectral lines of oxygen General properties Name, symbol, number oxygen, O, 8 Pronunciation /ˈɒksɨdʒən/ ok-si-jən Element category diatomic nonmetal, chalcogen Group, period, block 16 (chalcogens), 2, p Standard atomic weight 15.999(4) Electron configuration [He] 2s2 2p4 2, 6 Physical properties Phase gas Density (0 °C, 101.325 kPa) 1.429 g/L Liquid density at b.p. 1.141 g·cm−3 Melting point 54.36 K, -218.79 °C, -361.82 °F Boiling point 90.188 K, -182.962 °C, -297.332 °F Triple point 54.361 K, 0.1463 kPa Critical point 154.581 K, 5.043 MPa Heat of fusion (O2) 0.444 kJ·mol−1 Heat of vaporization (O2) 6.82 kJ·mol−1 Molar heat capacity (O2) 29.378 J·mol−1·K−1 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, −1, −2 Electronegativity 3.44 (Pauling scale) Ionization energies (more) 1st: 1313.9 kJ·mol−1 2nd: 3388.3 kJ·mol−1 3rd: 5300.5 kJ·mol−1 Covalent radius 66±2 pm Van der Waals radius 152 pm Miscellanea Crystal structure cubic Oxygen has a cubic crystal structure Magnetic ordering paramagnetic Thermal conductivity 26.58x10-3 W·m−1·K−1 Speed of sound (gas, 27 °C) 330 m·s−1 CAS registry number 7782-44-7 History Discovery Carl Wilhelm Scheele (1772) Named by Antoine Lavoisier (1777) Most stable isotopes Main article: Isotopes of oxygen iso NA half-life DM DE (MeV) DP 16O 99.76% 16O is stable with 8 neutrons 17O 0.039% 17O is stable with 9 neutrons 18O 0.201% 18O is stable with 10 neutrons v t e · references Blue white glow from an oxygen discharge tube. Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table and is a highly reactive nonmetallic element and oxidizing agent that readily forms compounds (notably oxides) with most elements.[1] By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium.[2] At STP, two atoms of the element bind to form dioxygen, a diatomic gas that is colorless, odorless, and tasteless, with the formula O 2. Many major classes of organic molecules in living organisms, such as proteins, nucleic acids, carbohydrates, and fats, contain oxygen, as do the major inorganic compounds that are constituents of animal shells, teeth, and bone. Most of the mass of living organisms is oxygen as it is a part of water, the major constituent of lifeforms (for example, about two-thirds of human body mass). Elemental oxygen is produced by cyanobacteria, algae and plants, and is used in cellular respiration for all complex life. Oxygen is toxic to obligately anaerobic organisms, which were the dominant form of early life on Earth until O 2 began to accumulate in the atmosphere. Free elemental O 2 only began to accumulate in the atmosphere about 2.5 billion years ago (see Great oxygenation event), about a billion years after the first appearance of these organisms.[3][4] Diatomic oxygen gas constitutes 20.8% of the volume of air.[5] Oxygen is the most abundant element by mass in the Earth's crust as part of oxide compounds such as silicon dioxide, making up almost half of the crust's mass.[6] Oxygen is an important part of the atmosphere, and is necessary to sustain most terrestrial life as it is used in respiration. However, it is too chemically reactive to remain a free element in Earth's atmosphere without being continuously replenished by the photosynthetic action of living organisms, which use the energy of sunlight to produce elemental oxygen from water. Another form (allotrope) of oxygen, ozone (O 3), strongly absorbs UVB radiation and consequently the high-altitude ozone layer helps protect the biosphere from ultraviolet radiation, but is a pollutant near the surface where it is a by-product of smog. At even higher low earth orbit altitudes, atomic oxygen is a significant presence and a cause of erosion for spacecraft.[7] Oxygen is produced industrially by fractional distillation of liquefied air, use of zeolites with pressure-cycling to concentrate oxygen from air, electrolysis of water and other means. Uses of elemental oxygen include the production of steel, plastics and textiles, brazing, welding and cutting of steels and other metals, rocket propellant, oxygen therapy and life support systems in aircraft, submarines, spaceflight and diving. Oxygen was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, and Joseph Priestley in Wiltshire, in 1774, but Priestley is often given priority because his work was published first. The name oxygen was coined in 1777 by Antoine Lavoisier,[8] whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. Its name derives from the Greek roots ὀξύς oxys, "acid", literally "sharp", referring to the sour taste of acids and -γενής -genes, "producer", literally "begetter", because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition. Contents [hide] 1 Characteristics 1.1 Structure 1.2 Allotropes 1.3 Physical properties 1.4 Isotopes and stellar origin 1.5 Occurrence 1.6 Analysis 2 Biological role of O2 2.1 Photosynthesis and respiration 2.2 Content in body 2.3 Build-up in the atmosphere 3 History 3.1 Early experiments 3.2 Phlogiston theory 3.3 Discovery 3.4 Lavoisier's contribution 3.5 Later history 4 Industrial production 5 Applications 5.1 Medical 5.2 Life support and recreational use 5.3 Industrial 6 Compounds 6.1 Oxides and other inorganic compounds 6.2 Organic compounds and biomolecules 7 Safety and precautions 7.1 Toxicity 7.2 Combustion and other hazards 8 See also 9 Notes 10 Citations 11 References 12 Further reading 13 External links Characteristics Structure Oxygen O2 molecule. At standard temperature and pressure, oxygen is a colorless, odorless gas with the molecular formula O 2, in which the two oxygen atoms are chemically bonded to each other with a spin triplet electron configuration. This bond has a bond order of two, and is often simplified in description as a double bond[9] or as a combination of one two-electron bond and two three-electron bonds.[10] Triplet oxygen (not to be confused with ozone, O 3) is the ground state of the O 2 molecule.[11] The electron configuration of the molecule has two unpaired electrons occupying two degenerate molecular orbitals.[a] These orbitals are classified as antibonding (weakening the bond order fr