What is ammonium or ammonium ion?

Ammonium or ammonium ion is a positively charges polyatomic cation with chemical formula, NH4+. The systematic IUPAC name of ammonium ion is azanium.

It is formed by the protonation of ammonia molecule and hence it is known as conjugate acid of ammonia. The pKa value of ammonium ion is 9.25.

The central ‘N’ atom in ammonium ion contains one lone pair of electron which is available for protonation. The nitrogen atom in ammonium ion is sp3 hybridized.

The ion has a tetrahedral geometry and is isoelectronic with methane and borohydride. In terms of size, the ammonium cation (rionic =175 pm) resembles the Cs+ cation (rionic =183 pm).

 

Ammonium ion formula and Lewis dot structure

 

Ammonium ion is the conjugate acid of ammonia. Ammonium ion is generated by the interaction of between weak base ammonia and proton donors Bronsted acids. The chemical formula of ammonium ion is NH4⁺. The Lewis dot structure of ammonium ion is shown below.