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The Element Oxygen

Oxygen ("Octium") is a chemical element in the periodic table that has the symbol O and atomic number 8. The element is very common, found not only on Earth but throughout the universe. Molecular oxygen (O2) (often called free oxygen) on Earth is thermodynamically unstable. Its initial appearance was due to the action of photosynthetic anaerobes and its ubiquity in later epochs has been largely facilitated by terrestrial plants, which release oxygen during photosynthesis.

Nitrogen Oxygen Fluorine
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Name, Symbol, Number Oxygen, O, 8
Chemical series nonmetals
Group, Period, Block 16 (VIA), 2 , p
Density, Hardness 1.429 kg/m3 (273K), NA
Appearance colorless
Atomic properties
Atomic weight 15.9994 amu
Atomic radius (calc.) 60 (48) pm
Covalent radius 73 pm
van der Waals radius 152 pm
Electron configuration [He]2s22p4
e- 's per energy level 2, 6
Oxidation states (Oxide) -2,-1 (neutral)
Crystal structure cubic
Physical properties
State of matter gas (paramagnetic)
Melting point 50.35 K (-368.77 F)
Boiling point 90.18 K (-297.08 F)
Molar volume 17.36 10-6 m3/mol
Heat of vaporization 3.4099 kJ/mol
Heat of fusion 0.22259 kJ/mol
Vapor pressure __ Pa at __ K
Speed of sound 317.5 m/s at 293 K
Electronegativity 3.44 (Pauling scale)
Specific heat capacity 920 J/(kg*K)
Electrical conductivity ND 106/m ohm
Thermal conductivity 0.02674 W/(m*K)
1st ionization potential 1313.9 kJ/mol
2nd ionization potential 3388.3 kJ/mol
3rd ionization potential 5300.5 kJ/mol
4th ionization potential 7469.2 kJ/mol
Most stable isotopes
iso NA half-life DM DE MeV DP
16O 99.762% O is stable with 8 neutrons
17O 0.038% O is stable with 9 neutrons
18O 0.2% O is stable with 10 neutrons
SI units & STP are used except where noted.

Notable characteristics

At standard temperature and pressure, oxygen is found as a gas consisting of two oxygen atoms, chemical formula O2. This oxygen is an important component of air, produced by plants during photosynthesis and is necessary for animals' respiration. The word oxygen derives from two words in Greek, the Greek oxus (acid) and geinomai (engender). (A misnomer, as there are many acids which do not contain oxygen.)

Liquid oxygen and solid oxygen have a light blue color and both are highly paramagnetic. Liquid oxygen is usually obtained by the fractional distillation of liquid air.


Oxygen finds considerable use as an oxidizer, with only fluorine having a higher electronegativity. Liquid oxygen finds use as an oxidizer in rocket propulsion. Oxygen is essential to respiration, so oxygen supplementation has found use in medicine. People who climb mountains or fly in airplanes sometimes have supplemental oxygen supplies (as air). Oxygen is used in welding, and in the making of steel and methanol.

Oxygen, as a mild euphoric, has a history of recreational use that extends into modern times. Oxygen bars can be seen at parties to this day. In the 19th century, oxygen was often mixed with nitrous oxide to promote a kind of analgesic effect.


Oxygen was discovered by the Swedish pharmacist Karl Wilhelm Scheele in 1771, but this discovery was not immediately recognized, and the independent discovery by Joseph Priestley on August 1st 1774 was more widely known. It was named by Antoine Laurent Lavoisier in 1774.


Oxygen is the most abundant element in the Earth's crust, estimated to comprise 46.7% of it. Oxygen comprises about 87% of the oceans (as H2O, water) and 20% of the atmosphere of Earth (as O2, molecular oxygen, or O3, ozone). Oxygen compounds, particularly metal oxides, silicates (SiO44-) and carbonates (CO32-), are commonly found in rocks and soil. Frozen water is a common solid on the outer planets and comets. The ice caps of Mars are made of frozen carbon dioxide. Oxygen compounds are found throughout the universeand the spectrum of oxygen is often seen in stars.


Due to its electronegativity, oxygen forms chemical bonds with almost all other elements (which is the origin of the original definition of oxidation). The only elements to escape the possibility of oxidation are a few of the noble gases. The most famous of these oxides is of course hydrogen oxide, or water (H2O). Other well known examples include compounds of carbon and oxygen, such as carbon dioxide (CO2), alcohols (R-OH), aldehydes, (R-CHO), and carboxylic acids (R-COOH). Oxygenated radicals such as chlorates (ClO3-), perchlorates (ClO4-), chromates (CrO42-), dichromates (Cr2O72-), permanganates (MnO4-), and nitrates (NO3-)are strong oxidizing agents in and of themselves. Many metals such as Iron bond with oxygen atoms, iron (III) oxide (Fe2O3). Ozone (O3) is formed by electrostatic discharge in the presence of molecular oxygen. A double oxygen molecule (O2)2 is known, found as a minor component of liquid oxygen. Epoxides are ethers in which the oxygen atom is part of a ring of three atoms.


Oxygen has three stable isotopes and ten known radioactive isotopes. The radioisotopes all have half lives of less than three minutes.


Oxygen can be toxic at elevated partial pressures.

Certain derivatives of oxygen, such as ozone (O3), hydrogen peroxide, hydroxyl radicals and superoxide, are also highly toxic. The body has developed mechanisms to protect against these toxic species. For instance, the naturally-occurring glutathione can act as an antioxidant, as can bilirubin which is normally a breakdown product of hemoglobin. Highly concentrated sources of oxygen promote rapid combustion and therefore are fire and explosion hazards in the presence of fuels. This is true as well of compounds of oxygen such as chlorates, perchlorates, dichromates, etc. Compounds with a high oxidative potential can often cause chemical burns.

The fire that killed the Apollo 1 crew on a test launchpad spread so rapidly because the pure oxygen atmosphere was at normal atmospheric pressure instead of the one third pressure that would be used during an actual launch. (see partial pressure)

See also


External links


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