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 and ubiquitous, found not only on Earth but throughout the universe. Molecular oxygen (O₂), as on Earth, is thermodynamically unstable, but exists through the action, first, of photosynthetic anaerobes and, in later epochs, of photosynthetic terrestrial plants.

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.

Applications

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.

History

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.

Occurrence

Oxygen is the most abundant element in the Earth's crust, estimated to comprise 46.7% of the crust. 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 (SiO₄^4-) and carbonates (CO₃^2-), 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 universe and the spectrum of oxygen is often seen in stars.

Compounds

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 (CrO₄^2-), dichromates (Cr₂O₇^2-), permanganates (MnO₄^-), and nitrates (NO₃^-)are strong oxidizing agents in and of themselves. Many metals such as Iron bond with oxygen atoms, Ferric 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.

Isotopes

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

Precautions

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

• Winkler test for dissolved oxygen for instructions on how to determine the amount of oxygen dissolved in fresh water.
• Combustion.
• Oxidation.
• The role of Oxygen as a diving breathing gas.

Reference

• Los Alamos National Laboratory – Oxygen

External links

• Los Alamos National Laboratory – Oxygen
• WebElements.com – Oxygen
• EnvironmentalChemistry.com – Oxygen
• It's Elemental – Oxygen
• Oxygen Therapy – The First 150 Years
• – Oxygen Toxicity

Oxygen is also the name of Oprah Winfrey's cable TV channel in the United States founded in 1998. Its programming targets women audience. See Oxygen Media.

mmO2 is a British telecommunications company specialising in mobile phones.