All salts are crystalline in nature and are called ionic solid. The ionic salts are formed by molecules containing positively charged, smaller in size cations and negatively charged relatively bigger anions. The charges on the ions and arrangement of the ions are such that they balance each other and the molecule is electrically neutral. Ionic solids are formed by the force of attraction between ions of opposite charges and force of repulsion between ions and some charges. These two opposite forces results into well ordered three dimensional arrangement of ions in ionic solids.
The actual arrangement of ions depends on three factors.
i) Sizes of the cation and anion.
ii) The charges on the ions.
iii) The ease with which the anion can be polarised.
The electrostatic forces of attraction between the nearest neighboring ions are very strong. The three dimensional arrangement of the cations and anions in the crystalline solids is such that the opposite forces are completely compensated. Therefore, the crystalline solids are hard and brittle and possess higher melting points. The crystalline solids are non conductors of electricity as free electrons are not available. In fused state or in aqueous solutions ions are available for conduction of electricity. On application of shearing force ionic crystals undergo distortion and fracture in crystal structure.