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~~'''~~Oxygen~~''' is a chemical [[element]]~~. ~~Its atomic number, derived from number of~~ [[~~proton~~]]s and ~~[[electron]]s it contains, is 8.~~ Oxygen'~~s atomic mass is slightly under 16, since it also has 8 [[neutron]]s (a slight amount of mass~~ is ~~"lost" in~~ the ~~energy contianed~~ in the ~~subatomic bonds)~~.

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{{Element | name=Oxygen | symbol=O | anumber=8 | amass=15.994 amu | state=gas | class=Non-metal | cstructure=Cubic | color=Colorless | date=1774 | discname=[[Joseph Priestley]] | origname=From the Greek words ''oxus'' (acid) and ''gennan'' (generate) | uses=Supports life | obtained=From liquid air}}

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'''Oxygen''' is the third most abundant element in the universe by mass and is essential to life on Earth.

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Under [[normal condition]]s it is a colorless, odorless [[gas]] consisting of two oxygen [[atom|atoms]] which has the chemical formula O2. This means it is diatomic. Approximately 20% of the [[atmosphere]] is made up of oxygen. Oxygen also forms a triatomic molecule called [[ozone]] (O3), which although unstable under normal conditions, is a very important ingredient in the upper atmosphere.

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==Chemical Properties==

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~~Oxygen is highly reactive, and in many other elements and compounds undergo~~ [[~~exothermic reaction~~]]~~s with it (they~~ [[~~combustion|burn~~]] ~~or rust~~). If it ~~were not for its continual replenishment~~ as a ~~waste product~~ of ~~plant [[photosynthesis]],~~ the ~~atmospheric~~ oxygen ~~would disappear~~, ~~forming compounds with other chemicals at the earth's surface~~.

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At normal [[atmospheric pressure]] oxygen melts at 54.36 [[Kelvin]] (K) and boils at 90.2 K; on Earth it essentially exists only as a gas. It readily dissolves in water, which makes aquatic life possible. Under normal conditions oxygen forms molecules consisting of two oxygen atoms each sharing two electrons in the 2p subshell; this form of oxygen is known as O2. O2 is a colorless, odourless gas. In liquid form (below -193 degrees Celsius) it is pale blue.

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Many animals depend upon oxygen as a highly efficient ingredient for breaking down food for energy, due to its reactivity. Those that do not are called "anaerobic", meaning "without air", and include many important bacteria.

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==Isotopes==

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[[~~Category:Chemistry~~]]

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There are three stable and 14 radioactive isotopes of oxygen. The stable isotopes are 16O, 17O and 18O, with 16O being by far the most common. Radioisotopes range from 10O to 26O, with the two most stable being 15O and 14O. This gives oxygen an atomic weight of slightly below 16.<ref>http://education.jlab.org/itselemental/iso008.html</ref>

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[[~~Category:Elements~~]]

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[[~~Category: hydrogen economy~~]]

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==Compounds==

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[[~~Category:gasses~~]]

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Oxygen is highly reactive. It reacts readily with most metals and many other elements, either through combustion or oxidation. As a result, many naturally occurring compounds contain oxygen.

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==Occurrence in Nature==

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Oxygen is the third most abundant element in the universe by mass after [[hydrogen]] and [[helium]]; approximately 5.9% of the mass of our [[solar system]] consists of oxygen. However, due to the large disparity in atomic weight between all isotopes of oxygen compared with 1H and 4He, less than 0.5% of the atoms in the solar system are oxygen atoms.{{fact}}

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Due to its reactivity free oxygen is extremely rare in nature and would not exist on Earth without the process of [[photosynthesis]]. Geologists and paleontologists believe that free oxygen first appeared during the "Great Oxygenation Event" around 2.4 billion years ago. Young-Earth creationists reject this timescale.

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==References==

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Revision as of 23:00, November 5, 2016