# Is a metallic bond the only type of chemical bonding a metal can exhibit?

Another common type of bonding is covalent coordinate bonding, in which a central metal atom is bound to 4-6 ligands. An example is nickel tetracarbonyl, $N i {\left(C O\right)}_{4}$, in which each $C O$ ligand contributes electron density to the central metal atom. The overlap of the CO orbitals with those of the $N i$ atom lowers the energy of the bonding electrons and keeps the ligands attached. This type of interaction is essentially a Lewis acid-base bond in which the ligand is the electron donor (base) and the metal is the electron acceptor (acid).
Metals can also form covalent bonds to first-row atoms like carbon and oxygen. Examples are iron oxide, $F {e}_{2} {O}_{3}$, and tetraethyllead, ${\left({C}_{2} {H}_{5}\right)}_{4} P b$, which was a gasoline additive that was phased out of automotive fuel in the 1970's.