Lesson 2: Valence Shell Electron Pair Repulsion (VSEPR) Theory

This is one of the most important lessons for predicting molecular geometry. The VSEPR theory is a simple yet powerful model for predicting the shapes of molecules.

• • Postulates of VSEPR Theory: Students will learn the core principles of VSEPR theory, including the idea that electron pairs (both bonding and lone pairs) around a central atom will arrange themselves to minimize repulsion.
  • Predicting Molecular Geometry: This is the practical application of the theory. The lesson provides a systematic way to predict the geometry of molecules with different numbers of electron pairs. For example, a molecule with four electron pairs (no lone pairs) will have a tetrahedral geometry, while one with two bonding pairs and two lone pairs (like water) will have a bent shape.

• Factors Affecting Geometry: The lesson also explains how lone pair-lone pair, lone pair-bond pair, and bond pair-bond pair repulsions vary, which helps explain the slight distortions from ideal geometries.