According to VSEPR theory, what is the molecular geometry of a molecule with three bonding pairs and one lone pair on the central atom?

• A. Bent
• B. Tetrahedral
• C. Trigonal pyramidal
• D. Trigonal planar

Answer: (C)

Verified step by step guidance

1. Identify the total number of electron pairs around the central atom by adding bonding pairs and lone pairs. Here, there are 3 bonding pairs and 1 lone pair, making a total of 4 electron pairs.
2. Recall that according to VSEPR theory, the electron pairs arrange themselves to minimize repulsion, so 4 electron pairs will adopt a tetrahedral electron geometry.
3. Understand that the molecular geometry depends on the positions of atoms (bonding pairs) only, while lone pairs affect the shape by repelling bonding pairs.
4. Since there is 1 lone pair and 3 bonding pairs, the molecular geometry is derived from a tetrahedral electron geometry but with one vertex occupied by a lone pair, resulting in a trigonal pyramidal shape.
5. Compare the options: 'Bent' corresponds to 2 bonding pairs and 2 lone pairs, 'Tetrahedral' corresponds to 4 bonding pairs, 'Trigonal planar' corresponds to 3 bonding pairs and 0 lone pairs, so the correct molecular geometry is 'Trigonal pyramidal'.