Question

The correct increasing order for bond angles among \( \text{BF}_3, \, \text{PF}_3, \, \text{and} \, \text{CF}_3 \) is:

• A. \( \text{PF}_3 \, < \, \text{BF}_3 \, < \, \text{CF}_3 \)
• B. \( \text{BF}_3 \, < \, \text{PF}_3 \, < \, \text{CF}_3 \)
• C. \( \text{CF}_3 \, < \, \text{PF}_3 \, < \, \text{BF}_3 \)
• D. \( \text{BF}_3 \, = \, \text{PF}_3 \, < \, \text{CF}_3 \)

Answer 1

The Correct Option is C

To rank the bond angles of \( \text{BF}_3, \, \text{PF}_3, \text{and} \, \text{CF}_3 \) in increasing order, we must examine their molecular geometry and electronic influences:

1. \( \text{BF}_3 \) (Boron Trifluoride) adopts a trigonal planar geometry due to the \( \text{sp}^2 \) hybridization of boron, resulting in bond angles of 120°.
2. \( \text{PF}_3 \) (Phosphorus Trifluoride) exhibits a trigonal pyramidal structure with \( \text{sp}^3 \) hybridized phosphorus. A lone pair on phosphorus reduces the bond angle from the ideal tetrahedral 109.5° to approximately 97°.
3. \( \text{CF}_3 \) (as seen in radicals like \( \text{CF}_3^+ \)) generally displays a trigonal planar arrangement comparable to \( \text{BF}_3 \). However, electronic factors such as resonance or inductive effects involving fluorine can cause its bond angle to deviate slightly from 120°.

Consequently, the bond angle characteristics are:

• \( \text{BF}_3 \) possesses the largest bond angle as it lacks lone pair repulsions.
• \( \text{PF}_3 \) has a smaller bond angle due to lone pair repulsion.
• The bond angle in \( \text{CF}_3 \) is modulated by resonance and inductive effects, rendering it smaller than the ideal angles found in \( \text{BF}_3 \) and \( \text{PF}_3 \).

Therefore, the bond angles in increasing order are:

\(\text{CF}_3 \, < \, \text{PF}_3 \, < \, \text{BF}_3\)