VSEPRSCH4U p 1of 7

VSEPR

VSEPR

-ValenceValence-shell electron-pair repulsion theory

-Molecules have many different shapes (linear, planar, complex 3D structures)

-The shape of a molecule determines many of its properties

-Shape of molecule is described in terms of bond lengths and bond angles

  • Length: distance between the centers of 2 bonded atoms
  • Angle: angle between the lines that join 2 atoms to a third atom

-Shape can be determined by computerized treatment of x-ray and spectral data

-Shape can be predicted by assuming that valence electrons pairs tend to stay as far from each other as possible

  • Basis for Valence Shell Electron Pair Repulsion (VSEPR) model

Steps to Predict VSEPR Molecular Shapes

Step 1: Draw the Lewis Structure

Step 2: Count the number of VSEPR pairs /ELECTRON DOMAINS around the central atom by using the VSEPR counting rules

1 VSEPR pair

= 1 single bond

= 1 double bond

= 1 triple bond

= 1 lone pair

Note: a single, a double, and a triple bond are all equivalent with respect to VSEPR pairs
Step 3: Pick the arrangement of VSEPR pairs (linear, tetrahedral, etc) that minimizes repulsion.

(Images taken from: and

Number of VSEPR pairs/Electron Domains / Picture / Angle / Shape
2 / / / Linear
3 / / Trigonal Planar
4 / / / Tetrahedral
5 / / / Trigonal Bipyramidal
6 / / / Octahedral

Step 4: Using the arrangement obtained in step 3, determine the shape of the molecule and the angles by taking into account the number of bonding pairs and the number of lone pairs

Step 5: Note which bond angles would be expanded or compressed by lone pair repulsion.

Number of VSEPR pairs,
Bonding pairs and lone pairs / Picture / Angle / Shape
VSEPR =2

BP=2

LP=0 / / / Linear
Number of VSEPR pairs,
Bonding pairs and lone pairs / Picture / Angle / Shape
VSEPR =3

BP=3

LP=0 / / / Trigonal Planar
VSEPR =3

BP=2

LP=1 / / / Bent

T

Number of VSEPR pairs,
Bonding pairs and lone pairs / Picture / Angle / Shape
VSEPR =4

BP=4

LP=0 / / / Tetrahedral
VSEPR =4

BP=3

LP=1 / / / Trigonal pyramidal
VSEPR =4

BP=2

LP=2 / / / Bent
Number of VSEPR pairs,
Bonding pairs and lone pairs / Picture / Angle / Shape
VSEPR =5

BP=5

LP=0 / / / Trigonal Bipyramidal
VSEPR =5

BP=4

LP=1 / / / See-Saw
(Distorted Tetrahedral)
VSEPR =5

BP=3

LP=2 / / / T-Shape
VSEPR =5

BP=2

LP=3 / / / Linear
Number of VSEPR pairs,
Bonding pairs and lone pairs / Picture / Angle / Shape
VSEPR =6

BP=6

LP=0 / / / Octahedral
VSEPR =6

BP=5

LP=1 / / / Square Pyramidal
VSEPR =6

BP=4

LP=2 / / / Square planar
VSEPR =6

BP=3

LP=3 / / / T-shape
VSEPR =6

BP=4

LP=2 / / / Linear