ValenceShellElectronPairRepulsion

What is VSEPR? VSEPR- Valence Shell Electron Pair Repulsion Lewis Structures are 2D Shapes, where as VSEPR Molecules are 3D Shapes VSEPR predicts the shape or “geometry” of the molecule Lone pairs of electrons influence the shape by pushing other atoms as far apart from each other as possible Constituent (definition): serving to compose or make up a thing; component (dictionary.com)

Key  Bonded electrons Lone pair electrons in the plane of the page forward backward Lone pair electrons 

Linear X—A—X A—A Bond angle: 180° 2 constituents around the central atom No lone pairs Examples: CO2 HCN F2 X—A—X or A—A

Trigonal Planar A X Bond angle: 120° 3 constituents around the central atom No lone pairs Examples: BF3 A X

Bent A X  Bond angle: < 120° 3 constituents around the central atom 1 lone pair Examples: SO2 O3 A X 

Tetrahedral A X Bond angle: 109.5° 4 constituents around the central atom No lone pairs Examples: CH4 A X

Trigonal Pyramidal A X  Bond angle: < 109.5° 4 constituents around the central atom 1 lone pair Examples: NH3 A X 

Bent A X  Bond angle: << 109.5° 4 constituents around the central atom 2 lone pairs Examples: H2O H2S  A X

VSEPR thought process Draw the Lewis structure. How many constituents around the central atom? What structure is this molecule based on (if all constituents were bonds)? Any atoms replaced by lone electron pairs? What is the final structure and angle? Helpful video: http://www.youtube.com/watch?v=nxebQZUVvTg

Example: PCl3 Lewis structure Number of constituents: 4 Base structure: tetrahedral One lone pair of electrons Final structure: trigonal pyramidal bond angle: < 109.5° P Cl 

Angle size: smallest to biggest Linear with 2 or 3 constituents: 180 Trigonal planar 3 constituents: 120  Bent with 3 constituents: < 120  Tetrahedral with 4 constituents: 109.5  Trigonal Pyramidal with 4 constituents: < 109.5° Bent with 4 constituents: << 109.5°