Oxygen

Oxygen is a <a href="/facts/Chemical_element/0jducgWD">chemical element</a>; it has <a href="/facts/Chemical_symbol/2Fe1VAL0">symbol</a> O and <a href="/facts/Atomic_number/bgAr581S">atomic number</a> 8. It is a member of the <a href="/facts/Chalcogen/nXLGmnqL">chalcogen</a> <a href="/facts/Group_(periodic_table)/YGBcUabv">group</a> in the <a href="/facts/Periodic_table/umdGIfUb">periodic table</a>, a highly <a href="/facts/Reactivity_(chemistry)/PuJ2pmRT">reactive</a> <a href="/facts/Nonmetal_(chemistry)/0oejKuzK">nonmetal</a>, and a potent <a href="/facts/Oxidizing_agent/1FQzB8pQ">oxidizing agent</a> that readily forms <a href="/facts/Oxide/DXtoVe1C">oxides</a> with most elements as well as with other <a href="/facts/Chemical_compound/37FXqqtv">compounds</a>. Oxygen is <a href="/facts/Abundance_of_elements_in_Earth%2527s_crust/UDSVHH56">the most abundant element in Earth's crust</a>, making up almost half of the <a href="/facts/Earth%2527s_crust/VSy2u31r">Earth's crust</a> in the form of various oxides such as <a href="/facts/Water/0lkXnJPK">water</a>, <a href="/facts/Carbon_dioxide/xGzpppEp">carbon dioxide</a>, <a href="/facts/Iron_oxide/KDo8hLWn">iron oxides</a> and <a href="/facts/Silicate/7NdthSRM">silicates</a>. It is <a href="/facts/Abundance_of_chemical_elements/CE9WehBl">the third-most abundant element in the universe</a> after <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a> and <a href="/facts/Helium/yRul93TG">helium</a>.
At <a href="/facts/Standard_temperature_and_pressure/JhJv9KFJ">standard temperature and pressure</a>, two oxygen atoms will <a href="/facts/Chemical_bond/ArNUMnIB">bind</a> <a href="/facts/Covalent_bond/EzMLf3Pz">covalently</a> to form <a href="/facts/Dioxygen/UVNYnKUQ">dioxygen</a>, a colorless and odorless <a href="/facts/Diatomic/hkfKAC7m">diatomic</a> gas with the <a href="/facts/Chemical_formula/hghUtthl">chemical formula</a> O2. Dioxygen gas currently constitutes approximately 20.95% <a href="/facts/Molar_fraction/nW4EepmJ">molar fraction</a> of the Earth's atmosphere, though this has <a href="/facts/Geological_history_of_oxygen/6VTugNzT">changed considerably</a> over long periods of time in <a href="/facts/Earth%2527s_history/0aEAQF0k">Earth's history</a>. A much rarer <a href="/facts/Triatomic/tMDw8gcY">triatomic</a> <a href="/facts/Allotropes_of_oxygen/UVNYnKUQ">allotrope of oxygen</a>, <a href="/facts/Ozone/o0E5gn2p">ozone</a> (O3), strongly absorbs the <a href="/facts/UVB/kncBUqn5">UVB</a> and <a href="/facts/Ultraviolet_C/kncBUqn5">UVC</a> wavelengths and forms a protective <a href="/facts/Ozone_layer/v4KfjalC">ozone layer</a> at the lower <a href="/facts/Stratosphere/taBra67V">stratosphere</a>, which shields the <a href="/facts/Biosphere/UpKAe1DB">biosphere</a> from <a href="/facts/Ionizing_radiation/vw0d9GaT">ionizing</a> <a href="/facts/Ultraviolet_radiation/kncBUqn5">ultraviolet radiation</a>. However, ozone present at the surface is a <a href="/facts/Corrosive/7LXjT1XE">corrosive</a> byproduct of <a href="/facts/Smog/5FYzS8sT">smog</a> and thus an <a href="/facts/Air_pollutant/zmk9Dy7S">air pollutant</a>.
All <a href="/facts/Eukaryotic/SkwyPLMA">eukaryotic</a> <a href="/facts/Organism/j8JkL09u">organisms</a>, including plants, animals, fungi, algae and most <a href="/facts/Protist/NYVfaGVz">protists</a>, need oxygen for <a href="/facts/Cellular_respiration/kb6gpsvL">cellular respiration</a>, a process that extracts <a href="/facts/Chemical_energy/Y3VP3Ifq">chemical energy</a> by the <a href="/facts/Dioxygen_in_biological_reactions/MW7vayxF">reaction of oxygen</a> with <a href="/facts/Organic_molecule/gqCNaN45">organic molecules</a> derived from food and releases carbon dioxide as a waste product. 
Many major classes of organic molecules in living organisms contain oxygen atoms, such as <a href="/facts/Protein/Jxmagu3E">proteins</a>, <a href="/facts/Nucleic_acid/2tTgcI0v">nucleic acids</a>, <a href="/facts/Carbohydrate/Geuuzxsf">carbohydrates</a> and <a href="/facts/Fat/87HcP11s">fats</a>, as do the major constituent <a href="/facts/Inorganic_compound/TfFfzxSz">inorganic compounds</a> 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 in Earth's atmosphere is produced by biotic <a href="/facts/Photosynthesis/TMV7w693">photosynthesis</a>, in which <a href="/facts/Photon_energy/Gy4zEAaE">photon energy</a> in sunlight is captured by <a href="/facts/Chlorophyll/1Sb0NyyM">chlorophyll</a> to split water molecules and then react with carbon dioxide to produce <a href="/facts/Carbohydrate/Geuuzxsf">carbohydrates</a> and oxygen is released as a <a href="/facts/Byproduct/qDosnqoD">byproduct</a>. Oxygen is too chemically reactive to remain a free element in air without being <a href="/facts/Oxygen_cycle/btlq2mXr">continuously replenished</a> by the photosynthetic activities of <a href="/facts/Autotroph/UDc8bzqD">autotrophs</a> such as <a href="/facts/Cyanobacteria/S8bKxIU9">cyanobacteria</a>, <a href="/facts/Chloroplast/fo8U3yTx">chloroplast</a>-bearing algae and plants.
Oxygen was isolated by <a href="/facts/Michael_Sendivogius/WgCSAq7V">Michael Sendivogius</a> before 1604, but it is commonly believed that the element was discovered independently by <a href="/facts/Carl_Wilhelm_Scheele/kcKBwyXa">Carl Wilhelm Scheele</a>, in <a href="/facts/Uppsala/X3HzSeYN">Uppsala</a>, in 1773 or earlier, and <a href="/facts/Joseph_Priestley/hQGV26wA">Joseph Priestley</a> in <a href="/facts/Wiltshire/42kKgE8r">Wiltshire</a>, 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 <a href="/facts/Antoine_Lavoisier/UheVQrhu">Antoine Lavoisier</a>, who first recognized oxygen as a chemical element and correctly characterized the role it plays in combustion.
Common industrial uses of oxygen include production of steel, plastics and textiles, <a href="/facts/Oxy-fuel_welding_and_cutting/Vkucvxsy">brazing, welding and cutting</a> of steels and other metals, <a href="/facts/Rocket_propellant/IyFhQEA2">rocket propellant</a>, <a href="/facts/Oxygen_therapy/38BdReab">oxygen therapy</a>, and <a href="/facts/Life_support_system/noqF51sS">life support systems</a> in aircraft, submarines, spaceflight and diving.

Oxygen open-in-new

Oxygen