VALENCE SHELL ELECTRON PAIR REPULSION (VSEPR) THEORY

The basic ideas of the valence shell electron pair repulsion (VSEPR) theory are:
Each set of valence shell electrons on a central atom is significant. The sets of valence shell electrons on the central atom repel one another. They are arranged about the central atom so that repulsions among them are as small as possible.

  1. Each bonded atom is counted as one region of high electron density, whether the bonding is single, double, or triple.
  2. Each unshared pair of valence electrons on the central atom is counted as one region of high electron density.

 

Number of Bonding Groups on the Central Atom Number of Lone Pair Electrons on the Central Atom
0 1 2 3 4
2

Example: CO2

 

Molecular Shape:

General Formula:
    AX2

Shape Name:
    Linear

Bond Angle(s):
    180o

       
3

Example: BCl3

Molecular Shape:


General Formula:
    AX3

Shape Name:
    trigonal planar

Bond Angle(s):
    120o

Example: SO2





Molecular Shape:

Generic Formula:
AX2E

Shape Name:
    bent or angular

Bond Angles:
    <120o

     
4

Example: CH4

Molecular Shape:

General Formula:
    AX4

Shape Name:
    tetrahedral

Bond Angle(s):
    109o

Example: NH3

Molecular Shape:


General Formula:
    AX3E

Shape Name:
    trigonal pyramidal

Bond Angle(s):
    107o

 

Example: H2O

Molecular Shape:


General Formula:
    AX2E2

Shape Name:
    bent or angular

Bond Angle(s):
    <107o

 		    
5

Example: PCl5

Molecular Shape:

General Formula:
     AX5

Shape Name:
     triginal bipyramidal

Bond Angles:
     90o, 120o, 180o

Example: SeCl4

Molecular Shape:

General Formula:
     AX4E

Shape Name:
     triginal bipyramidal

Bond Angles:
     <90o

Example: BrF5

Molecular Shape:

General Formula:
     AX3E2

Shape Name:
     triginal bipyramidal

Bond Angles:
     <90o

Example:

Molecular Shape:

General Formula:
     AX2E3

Shape:
      linear

Bond Angle:
      180o

 
6

Example:SF6

Moleculare Shape:

General Formula:
     AX6

Shape Name:
     octahedral

Bond Angles:
      90o

Example: IF4

Moleculare Shape:

General Formula:
     AX5E

Shape Name:
      square pyramidal

Bond Angles:
      <90o

Example: XeF4

Moleculare Shape:

General Formula:
     AX4E2

Shape Name:
      square planar

Bond Angles:
      <90o

Example:


Moleculare Shape:

General Formula:
     AX3E3

Shape Name:
      t-shape

Bond Angles:
      <90o

Example:

 

Moleculare Shape:

General Formula:
     AX2E4

Shape Name:
     linear

Bond Angles:
     180o