Explain the terms :
(a) Lone pair of electrons
(b) Coordinate bond
Explain diagrammatically the lone pair effect of:
(a) The nitrogen atom of the ammonia molecule leading to the formation of ammonium ions [NH4]+
(b) The oxygen atom of the H2O molecule leading to formation of hydronium [H3O]+ and hydroxyl ions [OH]-

(a) Lone pair of electrons — They are a pair of electrons not shared with any other atom.

(b) Coordinate Bond — It is a type of covalency which involves one of the combining atoms contributing both of the shared electrons. i.e., a bond formed by a shared pair of electrons with both electrons coming from the same atom.

(a) Formation of ammonium ions [NH₄]⁺

In ammonia, the ‘N’ atom contains one lone pair of electrons after completing it’s octet. This lone pair is accepted by the hydrogen ion of water leading to the formation of a coordinate covalent bond:

(b) Formation of hydronium (H₃O)⁺ and hydroxyl ions [OH]^–

In water, the ‘O’ atom contains two lone pairs of electrons after completing it’s octet. These lone pairs are accepted by the hydrogen ion leading to the formation of coordinate covalent bond:

−O − H