Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds. Oxygen is Earth's most abundant element, and after hydrogen and helium, it is the third-most abundant element in the universe. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. Diatomic oxygen gas currently constitutes 20. 95% of the Earth's atmosphere, though this has changed considerably over long periods of time. Oxygen makes up almost half of the Earth's crust in the form of oxides. All plants, animals, and fungi need oxygen for cellular respiration, which extracts energy by the reaction of oxygen with molecules derived from food and produces carbon dioxide as a waste product. In tetrapods breathing brings oxygen into the lungs where gas exchange takes place, carbon dioxide diffuses out of the blood, and oxygen diffuses into the blood. The body's circulatory system transports the oxygen to the cells, where cellular respiration takes place. Many major classes of organic molecules in living organisms contain oxygen atoms, such as proteins, nucleic acids, carbohydrates, and fats, as do the major constituent inorganic compounds of animal shells, teeth, and bone. Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms. Oxygen is continuously replenished in Earth's atmosphere by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form (allotrope) of oxygen, ozone (O3), strongly absorbs ultraviolet UVB radiation and the high-altitude ozone layer helps protect the biosphere from ultraviolet radiation. However, ozone present at the surface is a byproduct of smog and thus a pollutant.

Oxygen was isolated by Michael Sendivogius before 1604, but it is commonly believed that the element was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, and Joseph Priestley in Wiltshire, in 1774. Priority is often given for Priestley because his work was published first. Priestley, however, called oxygen "dephlogisticated air", and did not recognize it as a chemical element. The name oxygen was coined in 1777 by Antoine Lavoisier, who first recognized oxygen as a chemical element and correctly characterized the role it plays in combustion.

Common uses of oxygen include 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.

© Wikipedia | CC-by-SA-3.0 | Read more …

Atomic properties

Standard atomic weight15.999 ±0.001 [15.999 … 15.9997]
Atomic mass15.9991 u

Atomic radii

Radius (empirical)60 pm
Radius (calculated)48 pm
Covalent radius66 ±2 pm
Van der Waals radius152 pm

Atomic shell

Electron configurationHe 2s2 2p4
Ionization energy(1st) 13.618055 eV
(2nd) 35.12112 eV
(3rd) 54.93554 eV
(4th) 77.4135 eV
(5th) 113.899 eV
(6th) 138.1189 eV
Shell model

Physical properties

Density0.001429 g·cm−3 (273.1 K)
Molar volume1.736·10-5 m3·mol−1
Speed of sound317.5 m·s−1 (293 K)


Melting point54.36 K
Boiling point90.18 K
Liquid range35.82 K
Triple point54.36 K @ 0.1463 kPa
Critical point154.5 K @ 5.043 MPa
Transition temperature0.6 K


Melting enthalpy0.222 kJ·mol-1
Enthalpy of vaporization3.41 kJ·mol-1
Binding energy249 kJ·mol-1

Heat and conductivity

Specific heat capacity920 J·kg−1·K−1 (298 K)
Thermal conductivity0.02658 W·m-1·K-1


Magnetic susceptibility0.00345 cm3·mol−1 (293 K)

Optical properties

Refractive indexgaseous: 1
liquid: 1.221

Chemical properties

Oxidation state-2, -1, 0, +1, +2
Standard potential1.23 V


Pauling scale3.44
Sanderson scale3.65
Allred-Rochow scale3.5
Mulliken scale3.41
Allen scale3.61
Ghosh-Gupta scale8.786 eV
Boyd-Edgecombe scale3.62
Nagle scale3.62
Pearson absolute negativity7.54 eV

Other properties

Natural occurrenceprimordial
Crystal structureSimple cubic
Goldschmidt Classificationlithophile
Superconductorwith transition tempperature (solid body, normal pressure)
Price/kg0.154 USD

Natural abundances

1·107 ppb ≈ 1·1017 M☉
9·106 ppb ≈ 1.79·1016 Mt
4.1·108 ppb ≈ 410 kg
Earth’s crust
4.6·108 ppb ≈ 1.27·1010 Mt
8.57·108 ppb ≈ 1.17·106 Mt
Flowing water
8.8·108 ppb ≈ 14,000 Mt
Human body
6.1·108 ppb ≈ 42.6 kg