ABSTRACT
The type of chemical bond among the atoms in the class of molecules considered is usually called covalent, meaning that it occurs as a result of electrons being shared, so to speak, among distinct atoms. In the limiting case where there is total electron charge transfer, the bond is said to be ionic. The chemical bond holding together the structural units of a crystal may be classified, in some circumstances, as the already covalent or ionic bond. The classification of solids according to the chemical bonds within them, although useful, is not as sharp as that in electrical conductors and insulators. The bond keeping the crystal assembled it is referred to as metallic bond, which consists of the bond formed between the negatively charged electron "sea" into which a positive-ion lattice is submerged, with the electrostatic interaction acting as a "glue" for the entire system.
