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.{{fact}}

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.

==Isotopes==

==Isotopes==

==Compounds==

==Compounds==

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

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.

==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.{{fact}}

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.{{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 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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