Question

If oxygen is `"O"`, then what is `"O"_2` ?

Answer 1

Because it isn't stable as a single atom

Explanation:

It's true that Oxygen, can be termed as `"O"`. But one oxygen atom cant exist on its own, because its unstable.

Usually any atom needs 8 electrons in its outer orbit in order to stay stable.

But, the Oxygen atom has 6 electrons in its outer orbit. So, it needs two more electrons in order to make it 8. So, it makes a bond with another oxygen atom and shares 2 electrons each and becomes stable.

Its now represented as `"O"_2`

Answer 2

Well in the UK, `O_2` is a mobile telephone provider...but this is NOT what you asked....

Explanation:

As you say, `O`, is the oxygen atom....i.e. an atom that has 8 nuclear charges....and 8 electronic charges whizzing round the nuclear core. Oxygen is promiscuously reactive, and even in its unreacted state....the STABLE form is the oxygen molecule....i.e. `O_2`. Some punters (including me) even refer to `"dioxygen"` or `"dinitrogen"` to emphasize this condition.

And a simple VESPER treatment gives the electronic structure of dioxygen is...

`:stackrel(ddot)O=stackrel(ddot)O:`...i.e. this is conceived to derive from atomic....`2xx:ddotO:`, the which atom has SIX valence electrons…

With respect to dioxygen, molecular geometry is LINEAR....electronic geometry with respect to each atom is TRIGONAL PLANAR....