Changes

==Chemical Properties==

==Chemical Properties==

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 pale blue odourless gas.

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 pale blue odourless gas.{{fact}}

==Isotopes==

==Isotopes==

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.

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.{{fact}}

==Compounds==

==Compounds==

==Occurrence in Nature==

==Occurrence in Nature==

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.

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}}

Due to its reactivity free oxygen is extremely rare in nature and would not exist on Earth without the process of [[photosynthesis]]. Geologists and evolutionists believe that free oxygen first appeared during the "Great Oxygenation Event" around 2.4 billion years ago. Due to the extreme claimed age of this event the hypothesis is generally rejected by Creation scientists.

Due to its reactivity free oxygen is extremely rare in nature and would not exist on Earth without the process of [[photosynthesis]]. Geologists and evolutionists believe that free oxygen first appeared during the "Great Oxygenation Event" around 2.4 billion years ago. Due to the extreme claimed age of this event the hypothesis is generally rejected by Creation scientists.{{fact}}

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