Why does ammonia readily form a complex while ammonium ion does not?

Explanation

To understand why ammonia (NH₃) readily forms a complex while the ammonium ion (NH₄⁺) does not, we can break down the reasoning into a few key steps:

### Step 1: Structure of Ammonia
Ammonia (NH₃) is a neutral molecule that has a trigonal pyramidal structure. In this structure, the nitrogen atom has one lone pair of electrons.

### Step 2: Presence of Lone Pair
The lone pair of electrons on the nitrogen atom in ammonia can be donated to a metal ion to form a coordinate bond. This ability to donate a lone pair makes ammonia a good ligand, which can readily form complexes with metal ions.

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