What is electrovalent bond?

Electrovalent bond:

The electrostatic force of attraction which holds the oppositely charged ions together is known as ionic bond or electrovalent bond.

We can understand the formation of ionic bond by considering the examples of sodium chloride Na (1s² 2s² 2p⁶ 3s¹) has only one electron in the valence shell. It can acquire the stable electronic configuration of neon (15² 25² 2p⁶) by losing the electron. On the other hand chlorine atom (1s² 2s² 2p⁶ 3s² 3p⁵) has seven electron in its valence shell and it needs only one electron to complete its octet state. Thus both the atoms can complete their octet state if sodium atom gives one electron to chlorine atom. This tendency is responsible for bonding between sodium and chlorine atoms. Therefore sodium gives one electron and becomes positive charged Na⁺ ion, while chlorine takes up the electron and becomes negatively charged, Cl^– ion.

₁₁Na (1s² 2s² 2p⁵ 3s¹)              —> Na⁺ (1s² 25² 2p⁶) + e

₁₇Cl(1s² 2s² 2p⁶ 3s² 3p⁵) + e —> Cl^– (1s² 25² 2p⁶ 3s² 3p⁶)

Na⁺ + Cl^– —> NaCl

These two ions are then holding together by electrostatic force of attraction which constitutes the ionic bond.

General characteristics of electrovalent compound:

1. All ionic compounds are usually crystalline solids and are composed of ions even in the solid state.
2. Ionic solids have high melting points and boiling points due to the presence of strong attractive forces between the oppositely charged ions.
3. Ionic compounds have low volatility, high density and high stability.
4. These are highly soluble in polar solvents (such as water) having high dielectric constant but insoluble in organic solvents (such as benzene, alcohol, ether, etc.). However, some ionic compounds like BaSO₄, PbSO₄, AgCl, AgBr, AgI, etc are insoluble in water.
5. In molten state or in solution in polar solvents, ionic compounds are good conductors of electricity.
6. In solution, ionic compounds undergo ionic reactions which are very fast.
7. Crystals of certain ionic compounds have similar arrangement of atoms as well as geometry. Such crystalline compounds are called isomorphs and the phenomenon is called isomorphism. For example, ZnSO₄.7H₂O and FeSO₂.7H₂O are isomorphs. Also all alums show isomorphism.
8. Ionic bonds are non-directional and due to the non-directional nature of ionic bonds, ionic compounds do not show isomorphism.
9. Ionic compounds have high densities. This is so because the electrostatic force existing between the oppositely charged ions brings these ions close to each other. This results in decrease in volume of the crystal and hence increases in density.