Ionic or Electrovalent Bond
According to Kossel’s theory, in the process of formation of ionic bond the atoms acquire the noble gas electronic configuration by the gain or loss of electrons.
Example: Formation of NaCl
The electronic configuration of sodium atom (atomic number 11) is 2,8,1. Since it is highly electropositive, it readily loses an electron to attain the stable configuration of the nearest noble gas (neon) atom. It becomes a positively charged sodium cation (Na+) in the process.
Na → Na+ + e– ; ΔH = 493.8 kJ mol–1
On the other hand, a chlorine atom (electronic configuration: 2,8,7) requires one electron to acquire the stable electronic arrangement of an argon atom. It becomes a negatively charged chloride anion (Cl–) in the process.
Cl + e– → Cl– ; ΔH = –379.5 kJ mol–1
According to Kossel’s theory, there is a transfer of one electron from sodium atom to chlorine atom and both the atoms attain noble gas configuration.
The positively charged sodium ion and the negatively charged chloride ion are held together by electrostatic attractions. The bond so formed is called an electrovalent or an ionic bond. Thus, the ionic bond can be visualized as the electrostatic force of attraction that holds the cation and anion together. The compounds so formed are termed as ionic or electrovalent compounds.
Properties of Ionic Compounds
- These exist as crystalline solids in which the ions are arranged in a regular three dimensional structure. The ionic compounds are generally hard and brittle in nature.
- These compounds have high melting and boiling points due to strong electrostatic interactions between the ions.
- These are generally soluble in water and less soluble in non-polar solvents like ether, alcohol, etc.
- These conduct electricity when in molten state or in aqueous solutions.