gen-define-vsepr-theory-and-give-one-short-worked-example-eaa5

Define VSEPR theory and give one short worked example.

# VSEPR Theory **VSEPR (Valence Shell Electron Pair Repulsion) Theory** states that electron pairs around a central atom arrange themselves to minimize repulsion, adopting a geometry that maximizes the distance between them. ## Key Principles: - Both bonding pairs and lone pairs of electrons repel each other - Lone pairs repel more strongly than bonding pairs - The arrangement determines molecular shape --- ## Worked Example: NH₃ (Ammonia) **Step 1:** Count valence electrons - N: 5 valence electrons - H: 1 × 3 = 3 electrons - Total: 8 electrons (4 pairs) **Step 2:** Draw Lewis structure - N is central atom - 3 bonding pairs (N-H bonds) - 1 lone pair on nitrogen **Step 3:** Determine arrangement - 4 electron pairs → **tetrahedral electron geometry** - 3 bonding pairs + 1 lone pair → **trigonal pyramidal molecular shape** **Step 4:** Bond angle - Ideal tetrahedral = 109.5° - Actual in NH₃ ≈ 107° (lone pair compression) **Result:** NH₃ has a **trigonal pyramidal** shape with bond angles of approximately 107°.