Question

Among the following, the one having smallest bond angle is

• A. PH\(_3\)
• B. PF\(_3\)
• C. NF\(_3\)
• D. NH\(_3\)

Hint:

In molecules with trigonal pyramidal geometry, bond angles are affected by the electronegativity and size of the central atom. The more electronegative the atom, the higher the bond angle due to stronger electron pair repulsion.

Answer 1

The Correct Option is A

Step 1: Understanding the bond angle.
In molecules with a trigonal pyramidal shape like \( \text{NH}_3 \), \( \text{PH}_3 \), and \( \text{NF}_3 \), the bond angle is determined by the electron pair repulsion, which is the highest in the case of \( \text{NH}_3 \) (around 107°), and the lowest in the case of \( \text{PH}_3 \) (around 93.5°). This occurs due to the lower electronegativity of phosphorus compared to nitrogen, resulting in weaker repulsion between the bonding electrons in \( \text{PH}_3 \).
Step 2: Analyzing the options.
- (A) \( \text{PH}_3 \): The bond angle in \( \text{PH}_3 \) is the smallest due to weaker bonding electron repulsion. - (B) \( \text{PF}_3 \): The bond angle in \( \text{PF}_3 \) is smaller than in \( \text{NH}_3 \) but larger than in \( \text{PH}_3 \). - (C) \( \text{NF}_3 \): The bond angle is slightly smaller than \( \text{NH}_3 \), but larger than \( \text{PH}_3 \). - (D) \( \text{NH}_3 \): The bond angle in \( \text{NH}_3 \) is larger than in \( \text{PH}_3 \), but smaller than in ideal trigonal pyramidal geometry (107°).

Step 3: Conclusion.
The correct answer is (A) \( \text{PH}_3 \), as it has the smallest bond angle among the given molecules.