Metallic solids (consisting of a metallic bond) are formed exclusively by electropositive atoms (for example sodium, copper, aluminum), tending to give up their electrons which, however, having no electronegative atoms to join with, remain free.
The set of properties of metals suggests a structure in which the crystalline solid is made up of metal cations, obtained by the release of electrons from the valence shell — oscillating around the nodes of the crystal lattice, while the released electrons move in the entire lattice behaving as a kind of “electronic gas” (that permeates the entire crystal and is responsible for the stability of the crystal structure).
The structure of metallic crystals is often described as a uniform distribution of atomic nuclei within a “sea” of delocalized electrons. In a metallic bond, the valence electrons are not donated or shared as they are in ionic and covalent bonding. Rather, the electron clouds of adjacent atoms overlap so that electrons become delocalized. The electrons move with relative freedom from one atom to another throughout the crystal. This electron mobility means that metals are highly conductive of heat and electricity.
Metallic solids are opaque, lustrous solids that are both malleable and ductile. Malleable means they are soft and can be shaped or pressed into thin sheets, while ductile means they can be pulled into wires.
Metals tend to have high melting points, though notable exceptions are mercury.