The important bond chemicals linkage which hold together the components of crystalline solids and their general characteristics may be summarized as follows: 1. Ionic Linkages or ionic bond In which the crystals are made up of regular geometrical arrangements of positive and negative ions. Such solids tend to possess high melting and boiling points, are hard and difficult to deform, and tend to be soluble in polar solvents. When dissolved in such solvents as fused, they are excellent conductors. Crystals characterized by such linkages are called ionic crystals. The salts are examples. 2. Covalent Linkages In which the crystals are made up of molecules produced by the sharing of electrons, usually to pairs, between atoms of the elements involved. Such solids posses properties essentially opposite from those outlined for ionic crystals, although the partial ionic characters of many covalent bonds effect corresponding modifications. The following types of covalent crystalline soli