Question

The shape of the $N{H}_3$ molecule is:
A. Tetrahedral
B. Trigonal Planar
C. Trigonal Pyramidal
D. Linear

Answer 1

Hint: The structure of the $N{H}_3$ molecule is given in accordance to the VSEPR theory of chemical bonding. Also, bear in mind its structure is heavily affected by the presence of a lone pair of electrons on the Nitrogen atom.

Step-by-Step Solution:
Let us first understand the VSEPR theory of chemical bonding before moving on to the particulars of the structure of the $N{H}_3$ molecule.
The Valence Shell Electron Pair Repulsion Theory abbreviated as VSEPR theory is based on the premise that there is a repulsion between the pairs of valence electrons in all atoms, and the atoms will always tend to arrange themselves in a manner in which this electron pair repulsion is minimalized. This arrangement of the atom determines the geometry of the resulting molecule.
With this knowledge in mind, let us now attempt to predict the structure of the $N{H}_3$ molecule.
Ammonia has 4 regions of electron density around the central nitrogen atom (3 bonds and one lone pair). These are arranged in a tetrahedral shape. The resulting molecular shape is trigonal pyramidal with H-N-H angles of 106.7°. The structure of the same is illustrated as follows:

Therefore, by analysing the above structure, we can safely conclude that the answer to this question is c) Trigonal Pyramidal.

Note: The influence of the lone pair of electrons is key to this structure as their presence changes the molecular structure of $N{H}_3$ from tetrahedral to trigonal pyramidal. Be very wary of this distinction.