covalent bond

A covalent bond forms when two nonmetals share pairs of electrons instead of transferring them. Neither atom takes the electrons outright; instead both hold the shared pair in their outer shells, which is how both reach a more stable arrangement. Water, H₂O, is covalently bonded: each hydrogen shares its electron with the oxygen. Because the electrons are shared rather than handed over, a covalent compound is usually a set of molecules with lower melting points than an ionic solid, and it usually does not conduct electricity because there are no free ions. The classic error is to expect a covalent bond between a metal and a nonmetal; metals give electrons away and form ionic bonds, while covalent bonds form between nonmetals. The reverse mistake — treating two nonmetals as an ionic pair — is just as costly.