* Covalent bonds form when atoms share electrons to achieve a stable electron configuration (like having a full outer shell).

* Oxygen atoms have 6 electrons in their outer shell and need 2 more to achieve a stable octet.

* In an O2 molecule, each oxygen atom shares two electrons with the other oxygen atom, forming a double covalent bond. This sharing allows both oxygen atoms to achieve a stable electron configuration.

So, the two oxygen atoms in an O2 molecule are held together by a double covalent bond.