Ammonia: Strong or Weak Ligand? (NEET Chemistry)

Is ammonia a strong or weak ligand?

Hint: A ligand is a group or molecule that can donate electrons to the central metal atom in coordination complexes. Ligands can be either neutral or negatively charged entities. When a weak ligand is present, electron pairing does not occur, whereas with a strong ligand, electron pairing takes place.
Complete answer:

Ammonia is a molecule made up of one nitrogen atom and three hydrogen atoms. The nitrogen atom in ammonia contains a lone pair of electrons. Ammonia can donate these lone pairs to the central metal atom, allowing it to function as a ligand. It is an uncharged ligand, meaning the charge on ammonia ligands is zero.

The method by which the strength of ligands was determined was introduced in 1938. This was referred to as the spectrochemical series.

According to this series, the ligands were placed in the order of their capability of donating electrons.

$$I^{-}<B{r}^{-}<C{l}^{-}<F^{-}<ON{O}^{-}<O{H}^{-}<N{H}_3<N{O_2}^{-}<PP{h}_3<C{N}^{-}\approx CO$$

Ammonia is placed in the middle of the spectrochemical series.
It is a weak ligand but in presence of octahedral complexes containing a central metal atom belonging to 3d series has a coordination number of 3 , ammonia acts as a strong ligand.

For example, in the complex [Co(NH³)₆]³⁺ , Cobalt belongs to 3d series and has the oxidation number 3, in this case ammonia acts as a strong ligand.

Note:
Thus, according to spectrochemical series, we can understand that ammonia is a weak ligand but, in some cases, it acts as a strong ligand. It is a neutrally charged ligand with a lone pair of electrons on nitrogen atoms.