A covalent bond in which each atom contributes two electrons is called a double bond.

Here's why:

* Covalent bond: Atoms share electrons to achieve a stable electron configuration (like noble gases).

* Single bond: One pair of electrons is shared (one electron from each atom).

* Double bond: Two pairs of electrons are shared (two electrons from each atom).

Example:

In the molecule of oxygen (O2), each oxygen atom has six valence electrons. To achieve a stable octet, they share two pairs of electrons, forming a double bond.

This is represented as O=O, with the double line indicating the two shared pairs of electrons.