How is a metallic compound different from an ionic compound or a covalent compound?

Answer 1

Metallic compounds are very rare- substitutional alloys are not compounds (solid solutions) some alloy phases have a fixed stoichiometry. I suspect that you mean how do metals differ from ionic compounds or covalent compounds.

metallic bonding involves delocalisation of electrons and in the case of metals other than the straightforward group 1, group 2 metals and Al some covalency. The sea of electrons is a good description of the delocalisation- and this leads to conductivity. Metallic compounds are high melting, the metallic bond is strong particularly in the transition metals. The metallic bond copes with deformation of the lattice- and metals are generally malleable and ductile. However some lattice defects do form and this causes brittle fracture - metals are quite complex!

Ionic compounds consist of charged particles (atoms, polyatomic ions) that attract electrostaically and form rigid lattices. There are no electrons free to roam. Generally the ions are locked in place, so there is no electrical conductivity. the lattices are strongly bonded so they are high melting solids. The charged particles are potentially soluble in polar solvents such as water- so solubility is common.

Covalent compounds fall into two groups - molecular where there are discrete units - giant covalent compounds where there is a lattice of covalent bonds. A very few of these, notably graphite, do have delocalised electrons that can conduct electricity. The molecular compounds generally have low melting points as the units are held together by intermolecular forces and do not conduct electricity. Covalent molecules may be polar or non-polar- and this affects there solubilty- like dissolves like is the rule, e.g. polar solvents disolve polar molcules

Answer 2

A metallic compound consists of metal atoms held together by metallic bonds, which involve the sharing of electrons among atoms in a sea of delocalized electrons. Ionic compounds are formed by the transfer of electrons from a metal to a nonmetal, resulting in electrostatic attractions between ions. Covalent compounds involve the sharing of electrons between nonmetal atoms.