Question

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

Answer 1

No. Metallic bonds are formed in bulk metals like iron or copper, in which the orbitals of many metal atoms overlap each other to form highly delocalized orbitals. The atoms are essentially bound together by a 'sea' of shared electrons.

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, `Ni(CO)_4`, in which each `CO` ligand contributes electron density to the central metal atom. The overlap of the CO orbitals with those of the `Ni` 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, `Fe_2O_3`, and tetraethyllead, `(C_2H_5)_4Pb`, which was a gasoline additive that was phased out of automotive fuel in the 1970's.