Which of the following best describes the difference between trigonal planar and trigonal pyramidal molecular geometries?

• A. Trigonal pyramidal has all atoms in the same plane, while trigonal planar is three-dimensional.
• B. Trigonal planar and trigonal pyramidal both have the same bond angles and arrangement of atoms.
• C. Trigonal planar has all atoms in the same plane with no lone pairs on the central atom, while trigonal pyramidal has one lone pair on the central atom causing the shape to be three-dimensional.
• D. Trigonal planar has one lone pair on the central atom, while trigonal pyramidal has no lone pairs.

Answer: (C)

Verified step by step guidance

1. Understand the concept of molecular geometry: Molecular geometry describes the three-dimensional arrangement of atoms in a molecule. It is determined by the number of bonding pairs and lone pairs of electrons around the central atom, as predicted by the VSEPR (Valence Shell Electron Pair Repulsion) theory.
2. Define trigonal planar geometry: In a trigonal planar geometry, the central atom is surrounded by three bonding pairs of electrons, and there are no lone pairs on the central atom. The atoms are arranged in a flat, two-dimensional plane, and the bond angles are approximately 120°.
3. Define trigonal pyramidal geometry: In a trigonal pyramidal geometry, the central atom is surrounded by three bonding pairs of electrons and one lone pair. The lone pair causes a repulsion that pushes the bonding pairs downward, creating a three-dimensional shape. The bond angles are slightly less than 109.5° due to the lone pair repulsion.
4. Compare the two geometries: The key difference is that trigonal planar has no lone pairs on the central atom, resulting in a flat, planar structure, while trigonal pyramidal has one lone pair, making the shape three-dimensional.
5. Conclude with the correct description: The correct answer is that trigonal planar has all atoms in the same plane with no lone pairs on the central atom, while trigonal pyramidal has one lone pair on the central atom, causing the shape to be three-dimensional.