Which is the correct order of bond angle? A. Cl – P – Cl in, PCl3F2 > Cl – As – Cl in AsCl3F2 B. F – P – Cl in, PCl3F2 > F – As – Cl in AsCl3F2 C. F – P – F in, PCl3F2 < F – As – F in AsCl3F2 D. Cl – P – Cl in, PCl3F2 = Cl – As – Cl in AsCl3F2
The Correct Answer and Explanation is:
Correct answer: B. F – P – Cl in PCl3F2 > F – As – Cl in AsCl3F2
Explanation:
The bond angle in a molecule depends on several factors, such as the central atom’s size, electronegativity, hybridization, and the repulsion between bonding and nonbonding electron pairs.
PCl3F2 and AsCl3F2 are both trigonal bipyramidal in geometry. In such structures, the atoms can occupy either axial or equatorial positions. The bond angles are typically 90 degrees between axial and equatorial positions and 120 degrees between two equatorial positions.
In both molecules:
- Phosphorus (P) and arsenic (As) are in Group 15.
- However, phosphorus is smaller and more electronegative than arsenic.
Let us now analyze option B:
- In PCl3F2, the F – P – Cl angle involves a more electronegative and smaller central atom (phosphorus).
- In AsCl3F2, the same angle is slightly smaller due to the larger size and lower electronegativity of arsenic.
- A smaller central atom (like phosphorus) pulls bonded atoms closer together, but due to stronger electron repulsion among highly electronegative ligands (like F and Cl), the angle can be more expanded to minimize repulsion.
- As, being larger, allows more spatial flexibility, but its lower electronegativity results in weaker repulsions, which can cause bond angles like F – As – Cl to be slightly less.
Therefore, F – P – Cl has a greater bond angle than F – As – Cl, making option B the correct answer.
Options A, C, and D either incorrectly estimate equality or inverse relationships that do not align with periodic trends and electron repulsion principles.
