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:

$-\overset{|}{\underset{|}{\text{N}}} \rarr \text{H}$

(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:

$-\overset{|}{\text{O}}\rarr\text{H}$