Here's why:

* Electron Configuration: Oxygen has an electron configuration of 1s²2s²2p⁴. This means it has six electrons in its outermost shell (the 2nd shell).

* Valence Electrons: The valence electrons are the electrons in the outermost shell, which are involved in chemical bonding. Oxygen has six valence electrons.

* Octet Rule: Oxygen wants to achieve a stable octet (eight electrons) in its outermost shell. To do this, it needs to gain two more electrons.

* Bonding: This means oxygen can form two covalent bonds, sharing two electrons with other atoms.

Examples:

* In water (H₂O), oxygen forms two single bonds with two hydrogen atoms.

* In carbon dioxide (CO₂), oxygen forms two double bonds with a carbon atom.