Which model is used for predicting molecular geometry?

• A. Molecular orbital theory
• B. Valence-bond theory
• C. Hybridization theory
• D. VSEPR theory

Answer: (D)

Predicting molecular geometry comes from how electron pairs around a central atom repel each other. VSEPR theory says that electron domains—bonding pairs and lone pairs—arrange themselves as far apart as possible to minimize repulsion, giving shapes such as linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral. The number of electron domains determines the basic geometry, and lone pairs take up more space, tweaking bond angles away from ideal values. For example, water has two bonds and two lone pairs, which yields a bent shape; ammonia has three bonds and one lone pair, giving a trigonal pyramidal geometry; methane has four bonds and no lone pairs, resulting in a near-tetrahedral shape with angles around 109.5 degrees.

Other theories describe bonding in different ways—molecular orbital theory treats electrons in delocalized orbitals, while valence-bond theory and hybridization explain how bonds form and why certain bond angles occur. However, for directly predicting geometry from electron arrangements, the model that’s used is VSEPR.