Which of the following molecules has a molecular structure that differs from its electron-pair geometry?

• A. CH4
• B. CO2
• C. BF3
• D. NH3

Answer: (D)

Verified step by step guidance

1. Understand the difference between molecular structure (molecular geometry) and electron-pair geometry: Electron-pair geometry considers the positions of all electron groups (bonding and lone pairs) around the central atom, while molecular structure considers only the positions of atoms (bonding groups), ignoring lone pairs.
2. Analyze each molecule's Lewis structure to determine the number of bonding pairs and lone pairs on the central atom:
3. For CH4 (methane): The central carbon has 4 bonding pairs and 0 lone pairs, so molecular geometry and electron-pair geometry are both tetrahedral.
4. For CO2 (carbon dioxide): The central carbon has 2 double bonds and 0 lone pairs, so both molecular and electron-pair geometry are linear.
5. For BF3 (boron trifluoride): The central boron has 3 bonding pairs and 0 lone pairs, so both molecular and electron-pair geometry are trigonal planar.
6. For NH3 (ammonia): The central nitrogen has 3 bonding pairs and 1 lone pair, so the electron-pair geometry is tetrahedral, but the molecular geometry (shape) is trigonal pyramidal, which differs from the electron-pair geometry.