Chapter 12, Problem 45A

Interpretation Introduction

Interpretation:

The reason for the geometric structure of ammonia to not be described as tetrahedral needs to be explained.

Concept introduction:

Structure of molecule can be drawn using VSEPR theory. The total number of bonding and non-bonding pairs of electrons tells about the geometry of the molecule.

The valence electrons are the electrons present in outermost shell.

Answer to Problem 45A

Geometric structure is tetrahedral. But due to presence of lone pair of electrons its structure gets distorted and its shape is pyramidal according to VSEPR theory.

Explanation of Solution

Lewis structure of $N{H}_3$is:

  

Structure shows in $N{H}_3$ central atom nitrogen has three bond pairs and one lone pair. In total it has 4 pairs of electrons. Thus, its geometry is tetrahedral. But due to presence of lone pair of electrons its structure gets distorted and its shape is pyramidal according to VSEPR theory.

A normal tetrahedral bond has bond angle of $109\text{'}28\text{'}\text{'}$ but due to presence of lone pair bond angle is reduced to $107\text{'}$

Conclusion

Thus, ammonia has pyramidal shape due to presence of lone pair.