In which cases do you expect deviations from the idealized bond angle? Check all that apply.
CH3Br
PF3
SBr2
BC13
The Correct Answer and Explanation is :
Answer:
Deviations from the idealized bond angle are expected in the following cases:
✔ PF₃
✔ SBr₂
Explanation:
The idealized bond angles depend on the electron geometry, which is determined by the steric number (the sum of bonded atoms and lone pairs around the central atom). However, real bond angles may deviate due to lone pair repulsions, differences in electronegativity, and atomic size effects.
- CH₃Br (Methyl Bromide) – No Significant Deviation
- Molecular Geometry: Tetrahedral
- Ideal Bond Angle: 109.5°
- CH₃Br has four regions of electron density (three C-H bonds and one C-Br bond). The bromine atom is large, but it does not introduce lone pair repulsions that would significantly alter the bond angle.
- Minimal deviation is expected.
- PF₃ (Phosphorus Trifluoride) – Deviation Expected
- Molecular Geometry: Trigonal Pyramidal
- Ideal Bond Angle: ~109.5° (Tetrahedral Electron Geometry)
- Phosphorus has one lone pair, which repels the bonding pairs, pushing them closer together.
- The actual bond angle will be smaller than 109.5° due to lone pair-bond pair repulsion.
- SBr₂ (Sulfur Dibromide) – Deviation Expected
- Molecular Geometry: Bent (Angular)
- Ideal Bond Angle: ~109.5° (Tetrahedral Electron Geometry)
- Sulfur has two lone pairs, which exert strong repulsion on the S-Br bonds.
- This reduces the bond angle significantly below 109.5°.
- BCl₃ (Boron Trichloride) – No Significant Deviation
- Molecular Geometry: Trigonal Planar
- Ideal Bond Angle: 120°
- Boron has no lone pairs, and the three chlorine atoms are identical, so there are no significant repulsions to distort the bond angle.
- No deviation is expected.
Conclusion:
- PF₃ and SBr₂ show deviations due to lone pair repulsions.
- CH₃Br and BCl₃ closely follow their idealized bond angles.