Oxygen

Oxygen: a colourless, odourless, tasteless, [|non-metallic], gaseous element. Liquid and solid oxygen are pale blue. Its atomic number is 8, with a relative atomic mass of 15.9994. It is the most abundant element in the Earth's crust (almost 50% by mass), forms about 21% by volume of the atmosphere, and is present in combined form in water and many other substances. Oxygen is a by-product of [|photosynthesis] and the basis for [|respiration] in plants and animals.

Oxygen is very reactive and combines with all other elements except the [|noble gases] (rare gases) and fluorine. [|Combustion] (burning) and [|rusting] are two examples of reactions involving oxygen. Oxygen is also involved in the chemistry of breathing, where it is consumed (burned with food) to form carbon dioxide and water. Oxygen supports combustion. It is present in carbon dioxide, silicon dioxide (quartz), iron ore, calcium carbonate (limestone). In nature it exists as a molecule composed of two atoms (O2); single atoms of oxygen are very short-lived owing to their reactivity. They can be produced in electric sparks and by the Sun's ultraviolet radiation in the upper atmosphere, where they rapidly combine with molecular oxygen to form ozone (O3), an allotrope of oxygen.

Oxygen is obtained for industrial use, primarily for combustion, by the [|fractional distillation] of [|liquid air], by the [|electrolysis] of water, or by heating manganese(IV) oxide with potassium chlorate. In the laboratory it is prepared by the action of the [|catalyst] manganese(IV) oxide on hydrogen peroxide. It also finds some use in high-temperature oxyacetylene welding and cutting torches. The simple laboratory test for oxygen is that it relights a glowing spill.

Oxygen was independently discovered by [|Carl Wilhelm Scheele], in [|Uppsala] , in 1773 or earlier, and [|Joseph Priestley] in [|Wiltshire] , in 1774, but Priestley is often given priority because his work was published first. The name oxygen was coined in 1777 by [|Antoine Lavoisier], whose experiments with oxygen helped to discredit the then-popular [|phlogiston theory] of [|combustion] and [|corrosion]. [|Oxygen is produced industrially] by [|fractional distillation] of liquefied air, use of [|zeolites] with [|pressure-cycling] to concentrate oxygen from air, [|electrolysis of water] and other means. Uses of oxygen vary widely, ranging from the production of steel, plastics and textiles, [|rocket propellant], [|oxygen therapy] and [|combustion], where it produces energy, to uses in life support for aircraft, submarines, [|spaceflight] and [|diving].



Without oxygen nothing on planet Earth would survive. Plants, animals, humans and other organisms must have oxygen to survive.

There is no oxygen in space, therefore humans would not survive without space suits.

Physical properties
Oxygen is more [|soluble] in water than nitrogen is; water contains approximately 1 molecule of O2 for every 2 molecules of N2, compared to an atmospheric ratio of approximately 1:4. The solubility of oxygen in water is temperature-dependent, and about twice as much (14.6 mg·L−1) dissolves at 0 °C than at 20 °C (7.6 mg·L−1). [|[26]][|[27]] At 25 °C and 1 [|standard atmosphere] (101.3 [|kPa] ) of air, freshwater contains about 6.04 [|milliliters] (mL) of oxygen per [|liter], whereas [|seawater] contains about 4.95 mL per liter. [|[28]] At 5 °C the solubility increases to 9.0 mL (50% more than at 25 °C) per liter for water and 7.2 mL (45% more) per liter for sea water. Oxygen condenses at 90.20 [|K] (−182.95 °C, −297.31 °F), and freezes at 54.36 K (−218.79 °C, −361.82 °F). [|[29]] Both [|liquid] and [|solid] O2 are clear substances with a light [|sky-blue] color caused by absorption in the red (in contrast with the blue color of the sky, which is due to [|Rayleigh scattering] of blue light). High-purity liquid O2 is usually obtained by the [|fractional distillation] of liquefied air. [|[30]] Liquid oxygen may also be produced by condensation out of air, using liquid nitrogen as a coolant. It is a highly reactive substance and must be segregated from combustible materials. [|[31]]

Isotopes and stellar origin
Naturally occurring oxygen is composed of three stable [|isotopes], [|16O] , [|17O] , and [|18O] , with 16O being the most abundant (99.762% [|natural abundance] ). [|[32]] Most 16O is [|synthesized] at the end of the [|helium fusion] process in massive [|stars] but some is made in the [|neon burning process]. [|[33]] 17O is primarily made by the burning of hydrogen into [|helium] during the [|CNO cycle], making it a common isotope in the hydrogen burning zones of stars. [|[33]] Most 18O is produced when [|14N] (made abundant from CNO burning) captures a [|4He] nucleus, making 18O common in the helium-rich zones of [|evolved, massive stars]. [|[33]] Fourteen [|radioisotopes] have been characterized. The most stable are 15O with a [|half-life] of 122.24 seconds and 14O with a half-life of 70.606 seconds. [|[32]] All of the remaining [|radioactive] isotopes have half-lives that are less than 27 s and the majority of these have half-lives that are less than 83 milliseconds. [|[32]] The most common [|decay mode] of the isotopes lighter than 16O is [|β+ decay][|[34]][|[35]][|[36]] to yield nitrogen, and the most common mode for the isotopes heavier than 18O is [|beta decay] to yield [|fluorine]. [|[32]]

Photosynthesis and respiration
Photosynthesis splits water to liberate O2 and fixes CO2 into sugar. In nature, free oxygen is produced by the [|light-driven splitting] of water during oxygenic [|photosynthesis]. According to some estimates, [|Green algae] and [|cyanobacteria] in marine environments provide about 70% of the free oxygen produced on earth and the rest is produced by terrestrial plants. [|[42]] Other estimates of the oceanic contribution to atmospheric oxygen are higher, while some estimates are lower, suggesting oceans produce ~45% of Earth's atmospheric oxygen each year. [|[43]] A simplified overall formula for photosynthesis is: [|[44]] 6 CO2 + 6 H2O + [|photons] → C6H12O6 + 6 O2 (or simply [|carbon dioxide] + water + sunlight → [|glucose] + dioxygen) Photolytic [|oxygen evolution] occurs in the [|thylakoid membranes] of photosynthetic organisms and requires the energy of four [|photons]. [|[45]] Many steps are involved, but the result is the formation of a [|proton] gradient across the [|thylakoid membrane], which is used to synthesize [|ATP] via [|photophosphorylation]. [|[46]] The O2 remaining after oxidation of the water molecule is released into the atmosphere. [|[47]] Molecular dioxygen, O2, is essential for cellular respiration in all [|aerobic organisms]. Oxygen is used in [|mitochondria] to help generate adenosine triphosphate (ATP) during [|oxidative phosphorylation]. The reaction for aerobic respiration is essentially the reverse of photosynthesis and is simplified as: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 2880 kJ·mol−1 In [|vertebrates], O2 [|diffuses] through membranes in the lungs and into [|red blood cells]. [|Hemoglobin] binds O2, changing its color from bluish red to bright red [|[20]] ( CO2 is released from another part of hemoglobin through the [|Bohr effect] ). Other animals use [|hemocyanin] ( [|molluscs] and some [|arthropods] ) or [|hemerythrin] ( [|spiders] and [|lobsters] ). [|[38]] A liter of blood can dissolve 200 cm3 of O2. [|[38]] [|Reactive oxygen species], such as [|superoxide] ion ( O  − 2  ) and [|hydrogen peroxide] ( H2O2 ), are dangerous by-products of oxygen use in organisms. [|[38]] Parts of the [|immune system] of higher organisms, however, create peroxide, superoxide, and singlet oxygen to destroy invading microbes. Reactive oxygen species also play an important role in the [|hypersensitive response] of plants against pathogen attack. [|[46]]

An adult human in rest [|inhales] 1.8 to 2.4 grams of oxygen per minute. [|[48]] This amounts to more than 6 billion tonnes of oxygen inhaled by humanity per year. [|[49]]

Quick Facts:

An injured or ill person can benefit greatly from receiving air with a higher oxygen concentration.

The air a person normally breathes contains approximately 21 percent oxygen. The concentration of oxygen delivered to a victim through rescue breathing is 16 percent.

Without adequate oxygen, hypoxia, a condition in which insufficient oxygen reaches the cells, will occur.

**Signs and symptoms of hypoxia include**

Changes in level of consciousness.

Restlessness.

Cyanosis (bluish lips and nailbeds).

Chest pain

Always provide emergency oxygen to a victim having difficulty breathing if it is available, you are trained to use it and local protocols allow.

**Emergency oxygen should be considered if**

An adult is breathing fewer than 12 breaths per minute or more than 20 breaths per minute.

A child is breathing fewer than 15 breaths per minute or more than 30 breaths per minute.

An infant is breathing fewer than 25 breaths per minute or more than 50 breaths per minute.