Molecular Geometry Summary

Valence Shell Electron Pair Repulsion (VSEPR) Theory

• Predicts molecular shapes based on electron repulsion.

• Electrons prefer maximum distance from each other.

Molecular Geometries

Linear Geometry

• Molecules: BeCl₂, CO₂

• Shape: Straight line

• Bond angle: 180°

Trigonal Planar Geometry

• Molecule: BH₃

• Shape: Flat, tri-shaped

• Bond angle: 120° (360°/3)

Tetrahedral Geometry

• Molecule: CH₄ (methane)

• Shape: 3D, surrounds a central atom with four others

• Bond angle: 109.5°

• Example: SiF₄

Trigonal Pyramidal Geometry

• Molecule: NH₃ (ammonia)

• Shape: Similar to trigonal planar but with a lone pair

• Bond angle: ~107°

Bent Geometry

• Molecule: H₂O (water)

• Shape: Bent due to two lone pairs

• Bond angle: 104.5°

• Example: SO₂ (sulfur dioxide)

Comparison of Structures

• Tetrahedral (4 atoms) → Trigonal Pyramidal (3 atoms + 1 lone pair) → Bent (2 atoms + 2 lone pairs)

• Bond angles decrease as lone pairs increase.

• NH₃ has a bond angle of 107°; H₂O has a bond angle of 104.5°.