Final answer:
A double covalent bond joins two oxygen atoms, as each atom shares two electrons to fulfill the octet rule, resulting in an O=O structure. This type of bond is necessary for both oxygen atoms to achieve stability by having eight electrons in their valence shells.
Step-by-step explanation:
The bond that joins two oxygen atoms is a double covalent bond. An oxygen atom has six electrons in its valence shell; it requires two additional electrons to achieve a full octet and be chemically stable. In an oxygen molecule, two oxygen atoms each share two of their electrons to form a double covalent bond (O=O), allowing both atoms to reach the stable configuration of eight valence electrons.
Another example of a double covalent bond is in carbon dioxide (O=C=O), where two pairs of electrons are shared between the carbon and each oxygen atom. By contrast, single covalent bonds occur in molecules like water (H2O), where each hydrogen atom forms a single bond with oxygen, sharing just one pair of electrons.