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
Bonded electrons
in the plane of the page
forward
backward
Lone pair electrons

Key
Linear
X—A—X
or
A—A
 Bond angle: 180°
 2 constituents around
the central atom
 No lone pairs
 Examples:
– CO2
– HCN
– F2
Trigonal Planar
X
A
X
X
 Bond angle: 120°
 3 constituents around
the central atom
 No lone pairs
 Examples:
– BF3
Bent

A
X
X
 Bond angle: < 120°
 3 constituents around the
central atom
 1 lone pair
 Examples:
– SO2
– O3
Tetrahedral
X
A
X
X
X
 Bond angle: 109.5°
 4 constituents around
the central atom
 No lone pairs
 Examples:
– CH4
Trigonal Pyramidal

A
X
X
X
 Bond angle: < 109.5°
 4 constituents around the
central atom
 1 lone pair
 Examples:
– NH3
Bent
A
X
X
 Bond angle: << 109.5°
 4 constituents around the
central atom
 2 lone pairs
 Examples:
– H2O
– H2S
VSEPR thought process
1. Draw the Lewis structure.
2. How many constituents around the central
atom?
3. What structure is this molecule based on (if
all constituents were bonds)?
4. Any atoms replaced by lone electron pairs?
5. What is the final structure and angle?
Example: PCl3
1. Lewis structure
2. Number of constituents: 4
3. Base structure: tetrahedral
4. One lone pair of electrons
5. Final structure: trigonal pyramidal
bond angle: < 109.5°

P
Cl
Cl
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°