Covalent bonds tend to be strong bonds and produce molecules and crystals that are electrical insulators. Another way for an atom to achieve a completely filled outer shell of electrons is for it to lose or gain a sufficient number of electrons. An ionic bond is one in which there has been a complete transfer of electrons from the atom of one element to the atom of the other element. The ions so formed are held together by the electrostatic attraction between oppositely charged particles. Bonding in most of the minerals we geologists deal with is largely ionic, however, covalent bonding does occur to a lesser degree.
Metals are elements whose atoms easily lose their outer electrons.
In a typical metal there are more bond sites, or empty orbitals, than there are electron pairs to fill them. Detached electrons are dispersed among the atoms in the structure and are free to move about. This electron mobility, of course, is responsible for the good electrical conductivity of metals. Metallic bonding is found in native metals and to a lesser degree in some sulfides and arsenides. The extremely weak bonds that arise from slight imbalance of charge between two atoms or groups of atoms which otherwise have electrical neutrality.