|Atomic number (Z)||8|
|Group||group 16 (chalcogens)|
|Element category||reactive nonmetal|
|Electron configuration||[He] 2s2 2p4|
|Electrons per shell||2, 6|
Oxygen is the most copious chemical element by mass in the Earth's environment, air, sea, and land. Oxygen is the 3rdmostcopious chemical element in the world, after hydrogen and helium. About 0.8% of the Sun's mass is oxygen. Oxygen constitutes 49.3% of the Earth's crust by mass as part of oxide compounds like silicon dioxide and is the most copious element by mass in the Earth's crust. It is also the main component of the oceans (88.9% by mass). Oxygen gas is the 2ndsimplest component of the Earth's atmosphere, taking up 20.9% of its volume and 23.1% of its mass (some 10 tons). Earth is rare among the planets of the Solar System in having such a great concentration of oxygen gas in its atmosphere: Mars (with 0.1% O2 by volume) and Venus have much less. The O2 surrounding those planets is made solely by the action of ultraviolet radiation (UV) on oxygen-containing molecules such as carbon dioxide CO2.
|5 °C||25 °C|
|Freshwater||9.0 mL||6.04 mL|
|Seawater||7.2 mL||4.95 mL|
At customary pressure and temperature, oxygen is an odorless, colorless and tasteless gas with the molecular formula O2, mentioned to as dioxygen.
Oxygen storage technique includes cryogenics, high-pressure oxygen tanks, and chemical compounds. For reasons of economy, oxygen is often conveyed in bulk as a liquid in particularly insulated tankers, since one liter of liquefied oxygen is equal to 840 liters of gaseous oxygen at atmospheric pressure and 22 °C (70 °F). Such tankers are used to replenish bulk liquid oxygen storage bottles, which stand outside hospitals and other institutes that need great volumes of pure oxygen gas. Liquid oxygen is passed through heat exchangers, which transform the cryogenic liquid into gas before it arrives in the building. Oxygen is also stored and transported in smaller cylinders having the compressed gas; a form that is useful in some portable medical applications and oxy-fuel welding and cutting.
Photosynthesis and respiration