122.

What is an ionic bond? How is it formed? Illustrate with suitable examples.

Ionic or electrovalent bond: The electrostatic force of attraction between the oppositely charged ions is known as an ionic bond. It is formed by the complete transference of one or more valence electrons of one atom to the valence shell of the other atom so that each atom acquires the nearest noble gas configuration. The compounds containing ionic or electrovalent bonds are called ionic or electrovalent compounds. The number of electrons which an atom loses or gains while forming an ionic bond is known as electrovalency. Examples :

(i) Formation of NaCl: The electronic configuration of sodium (Z= 11) and chlorine (Z= 17) can be represented as:.



Thus, one electron gets transferred from Na atom to chlorine atom. This gives rise to Na⁺ and Cl^– ions having a noble gas configuration. These ions are held together by the electrostatic force of attraction known as an ionic bond.



(ii) Formation of CaF₂. The electronic configuration of calcium (Z = 20) and fluorine (Z = 9) can be represented as,

₂₀Ca = 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² (2, 8, 8, 2)
₉F = 1s² 2s² 2p⁵ (2, 7)

Thus, calcium atom loses two valence electrons to two fluorine atoms each of which gains one electron. This leads to the formation of Ca²⁺ ion and two F“ ions each of which has a stable noble gas configuration. These oppositely charged ions are mutually attracted by the electrostatic force of attraction which constitute ionic bonds.



(iii) Formation of MgO: The electronic configuration of magnesium (Z = 12) and oxygen (Z = 8) can be represented as:

₁₂Mg= 1s² 2s² 2p⁶ 3s² (2, 8, 2)
₈O = 1s² 2s² 2p⁴ (2, 6)

Magnesium atom loses two valence electrons to an oxygen atom. Thus, Mg²⁺ and O^2– ions are formed each of which has a stable noble gas configuration. These ions are held together by the electostatic force of attraction which constitutes ionic bond.