Exactly as the title asks.
Pure oxygen is generally represented as O2 yet oxygen is an element of the periodic table. Why is it O2 and not just O?
Oxygen is found in 3 forms: nascent (O), molecular (O2, the most common) and ozone (O3). Nascent oxygen, due to its electronic configuration (i.e how many electrons it has and how they’re spread out across its electronic shells) is unstable, and tends to quickly form bonds with another O, forming O2. This is also the case e.g. for hydrogen, which is usually found as H2.
You can find O in this form in some environments, in the upper atmosphere there is enough UV radiation to break up O2 into O.
So simply because it’s so reactive the most common form is oxygen paired with itself?
This is an ELI5 explanation. Well done💯💯
Not just with itself, also with other elements. Say, you won’t find pure iron in the wild either, because normally it reacts with oxygen so well.
But yea oxygen needs to pair with something because its outer electron shell is incomplete. So pairing with another oxygen atom is likely, but also with whatever else is available - nitrogen, iron, whatever.
Most elements are found in molecules really, with the exception of noble gasses like Helium. And some are less reactive than others.
