What is the molecular geometry of a molecule with three bonding pairs and no lone pairs around the central atom?

Analysis

The question asks for the molecular geometry of a central atom that has exactly three bonding pairs of electrons and zero lone pairs. This is a classic application of the Valence Shell Electron Pair Repulsion (VSEPR) theory.

Concept Explanation

The VSEPR theory states that electron pairs around a central atom arrange themselves as far apart as possible to minimize repulsion. The geometry is determined by the total number of electron domains (bonding pairs + lone pairs):

• 2 bonding pairs, 0 lone pairs: Linear (180°)
• 3 bonding pairs, 0 lone pairs: Trigonal planar (120°)
• 4 bonding pairs, 0 lone pairs: Tetrahedral (109.5°)
• 6 bonding pairs, 0 lone pairs: Octahedral (90°)

When there are three bonding pairs and no lone pairs, the three bonds spread out in a flat, triangular shape to maximize the distance between them, resulting in a bond angle of 120°.

Step-by-Step Solution

1. Identify the electron domains: The problem specifies 3 bonding pairs and 0 lone pairs.
2. Calculate total domains: $3 + 0 = 3$ total electron domains.
3. Apply VSEPR rules: • For 3 domains, the most stable arrangement that minimizes repulsion is a flat triangle. • This geometry is known as Trigonal planar.
4. Compare with options: • A (Tetrahedral) requires 4 bonding pairs. • B (Trigonal planar) matches our calculation of 3 bonding pairs. • C (Linear) requires 2 bonding pairs. • D (Octahedral) requires 6 bonding pairs.

Conclusion

The molecular geometry for a molecule with three bonding pairs and no lone pairs is Trigonal planar.

Exam Tip: Remember the "3-3-3" rule for your exams: 3 electron pairs, 3 bonds, 3-sided shape (Trigonal planar). If you ever forget, just visualize a triangle—it has three sides and three corners!