What type of chemical bond forms when two atoms share pairs of electrons?

A covalent bond forms when two atoms share pairs of electrons. The shared electrons are attracted to the nuclei of both atoms, helping hold the atoms together in a molecule or network solid.

Atoms commonly form covalent bonds because sharing electrons can give them a more stable outer electron arrangement. In a hydrogen molecule, for example, two hydrogen atoms share one pair of electrons, forming a single covalent bond. Oxygen and nitrogen can share two or three pairs, producing double and triple bonds respectively.

Covalent bonds are especially common between nonmetal atoms and can be polar or nonpolar. In a nonpolar bond, such as the bond between two identical oxygen atoms, the electrons are shared fairly evenly. In water, oxygen attracts the shared electrons more strongly than hydrogen, so the O–H bonds are polar.

A covalent bond is different from an ionic bond, in which electrons are transferred and oppositely charged ions attract one another. A hydrogen bond is also different: it is a weaker intermolecular attraction, not the primary bond holding the atoms within a water molecule together. Covalent bonding can create small molecules such as methane or giant structures such as diamond.