Question

The shape of ${\mathrm{NH}}_3$ molecule is:

• A. tetrahedral
• B. trigonal planar
• C. trigonal pyramidal
• D. linear

Answer 1

The correct option is C

trigonal pyramidal

Explanation for correct option:

C. Trigonal pyramidal

Step 1: Hybridization:

• “Hybridization is defined as the process of intermixing of the orbitals of slightly different energies so as to redistribute their energies, resulting in the formation of a new set of orbitals of equivalent energies and shape.”

Step 2: Formula used for calculation:

• $\mathrm{Steric}\mathrm{number}=\frac{1}{2}\left(\mathrm{V}+\mathrm{M}-\mathrm{C}+\mathrm{A}\right)$
• Where V is the number of valence electrons, M is the monovalent electron, C is the positive charge and A represents the negative charge.

Step 3: Calculation for Hybridisation and shape of ${\mathrm{NH}}_3$:

• The total number of valence electrons of N in ${\mathrm{NH}}_3$ is 5 and there is 3 monovalent atom.
• $$\begin{gathered} \mathrm{Steric}\mathrm{number}=\frac{1}{2}\left(5+3\right) \\ \mathrm{Steric}\mathrm{number}=\frac{1}{2}\times 8=4 \end{gathered}$$
• The steric number is 4, thus the hybridization of ${\mathrm{NH}}_3$ is ${\mathrm{sp}}^3$.
• As per VSEPR, the geometry of ${\mathrm{sp}}^3$ hybridization is trigonal pyramidal and tetrahedral shape.

Explanation for incorrect options:

The shape of the ammonia molecule is trigonal pyramidal. Thus options A, B, and D are incorrect.

Hence, the correct option is C i.e. trigonal pyramidal.