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 a trigonal bipyramidal geometry, which consists of three types of bond angles. 
- The axial bonds (marked as a) are between the central atom and the two atoms directly above and below it. These bond angles are 180°. 
- The equatorial bonds (marked as b) are between the central atom and the three atoms in the same plane as it. These bond angles are 120°. 
- The bond angles between the two axial bonds (marked as c) are between 90° and 120°, depending on the size of the atoms attached to the central atom. In this case, since all the atoms attached to the central atom are the same, the bond angle c is 120°.

Therefore, the bond angles marked a, b, and c are about 180°, 120°, and 120°, respectively, which corresponds to choice C.

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