what is a covalent bond?

A covalent bond, also called a molecular bond, is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The chemical bond formed when electrons are shared between two atoms, usually each atom contributes one electron to form a pair of electrons that are shared by both atoms, which then allow the atoms to fullfill the octet rule; a chemical rule of thumb that reflects observation that atoms of main-group elements tend to combine in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas.