The bond angles marked a, b, and c in the molecule below are about ________, ________, and ________, respectively.
A)109.5°, 109.5°, 109.5°
B)120°, 109.5°, 120°
C)109.5°, 109.5°, 120°
D)90°, 180°, 90°
E)109.5°, 109.5°, 90°

Question

The bond angles marked a, b, and c in the molecule below are about ________, ________, and ________, respectively. 
A)109.5°, 109.5°, 109.5° 
B)120°, 109.5°, 120° 
C)109.5°, 109.5°, 120° 
D)90°, 180°, 90° 
E)109.5°, 109.5°, 90°

Quizplus · Accepted Answer

The molecule shown is trigonal planar, meaning that it has a central atom (C) with three bonded atoms (two H and one Cl) arranged in a flat triangle. Since the electron pairs around C will repel each other to maximize their distance, the bond angles will be spread out as evenly as possible. In trigonal planar molecules, this means that all three bond angles will be equal to 120°. However, when one of the bonded atoms is replaced with a lone pair (as in ClO2-), the lone pair will exert greater repulsion than a bonded atom, causing the bond angles adjacent to it to be slightly smaller than 120°. Therefore, angles a and b will both be approximately 109.5° (the tetrahedral angle), while angle c will be closer to 120°. Choice C is the only one that reflects this pattern.

The Bond Angles Marked A, B, and C in the Molecule