Which of the following best describes the O–S–O bond angle in the SO_2 molecule?

• A. Exactly 90°
• B. Approximately 109.5°
• C. Approximately 120°
• D. Exactly 180°

Answer: (C)

Verified step by step guidance

1. Step 1: Identify the molecular geometry of SO_2 by considering its Lewis structure. Draw the Lewis structure showing sulfur (S) bonded to two oxygen (O) atoms, and include any lone pairs on the sulfur atom.
2. Step 2: Determine the number of electron regions (bonding and lone pairs) around the central sulfur atom. This will help predict the electron geometry using the VSEPR (Valence Shell Electron Pair Repulsion) theory.
3. Step 3: Use VSEPR theory to predict the molecular shape based on the electron regions. For SO_2, the presence of a lone pair on sulfur and two bonded oxygen atoms results in a bent or angular shape.
4. Step 4: Recall that a bent molecular shape with three electron regions (two bonding pairs and one lone pair) typically has a bond angle slightly less than the ideal trigonal planar angle of 120°, due to lone pair repulsion compressing the bond angle.
5. Step 5: Conclude that the O–S–O bond angle in SO_2 is approximately 120°, which matches the trigonal planar electron geometry but is slightly less due to the lone pair on sulfur.