Changes

'''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).

'''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 bond]]s).

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.

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 [[diatom]]ic.  Approximately 20% of the [[atmosphere]] is made up of oxygen.  Oxygen also forms a [[triatom]]ic molecule called [[ozone]] (O₃), which although unstable under normal conditions, is a very important ingredient in the upper [[atmosphere]].

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.

Oxygen is highly reactive, and in many other elements and compounds undergo [[exothermic reaction]]s with it (they [[combustion|burn]] or [[oxidization|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.

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.

Many [[animal]]s 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]].

[[Category:Chemistry]]

[[Category:Chemistry]]