Mastodawn

Why is pure oxygen called O2 when oxygen is an element?

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?

There are 7 elements that will naturally form covalent bonds with themselves.
Here is how to remember these diatomic elements:

(H)ave (N)o (F)ear (O)f (I)ce (Cl)old (Br)eer.
The Ice is solid, the beer is liquid, and everything else is a gas.

And who doesn’t enjoy cracking open a nice clold breer?