Properties of electrovalent (or) ionic compounds
Ionic compounds possess characteristic properties of their own like physical state, solubility, melting point, boiling point and conductivity. The nature of these properties are discussed as follows.
Due to strong coulombic forces of attraction between the oppositely charged ions, electrovalent compounds exist mostly as hard
crystalline solids. Due to the hardness and high lattice enthalpy, low volatility, high melting and boiling points are seen.
Because of the strong electrostatic forces, the ions in the solid are not free to move and act as poor conductor of electricity in the solid state. However, in the molten state, or in solution, due to the mobility of the ions electrovalent compounds become good conductor of electricity.
Ionic compounds possess characteristic lattice enthalpies since they exist only as ions packed in a definite three dimensional manner. They do not exist as single neutral molecule or ion.
Ionic compounds are considered as polar and are therefore, soluble in high dielectric constant solvents like water. In solution, due to solvation of ions by the solvent molecules, the strong interionic attractions are weakened and exist as separated ions.
Electrovalent compounds having the same electronic configuration exhibit isomorphism.
Ionic (or) Electrovalent bond
The electrostatic attraction force existing between the cation and the anion produced by the electron transfer from one atom to the other is known as the ionic (or) electrovalent bond. The compounds containing such a bond are referred to as ionic (or) electrovalent compounds.
Ionic bond is non directional and extends in all directions. Therefore, in solid state single ionic molecules do not exist as such. Only a network of cations and anions which are tightly held together by electro-static forces exist in the ionic solids. To form a stable ionic compound there must be a net lowering of energy. That is, energy is released as a result of electovalent bond formation between positive and negative ions.
When the electronegativity difference between the interacting atoms are greatly different they will form an ionic bond. In fact, a difference of 2 or more is necessary for the formation of an ionic bond. Na has electronegativity 0.9 while Cl has 3.0, thus Na and Cl atoms when brought together will form an ionic bond.