Class 11 Chemistry Chemical Bonding Structure VSEPR THEORY


Geometry of molecule

  • It is the relative arrangement of bonded atoms in a molecule.
  • The way in which the bonded atoms direct themselves around the central atom is explained on the basis of this theory.
  • This theory was given by Sid wick and Favell.
  • In this only the valence electrons participate in bond formation.
  • The bonded atoms around central metal atom will have repulsions between them
  • Therefore, they will arrange themselves in such way that the repulsion is minimum.

In BF3 the arrangement is like it is shown below:



To minimize the repulsion, the fluorine directs them around boron in such a way as shown above in figure.

Postulates of VSEPR theory

The basic idea behind it is that the bonded atoms in a molecule adopt the particular arrangement in space around the central metal atom which keeps them as far as possible.


  1. The shape of molecule depends upon the number of valence shell electron pairs.
  • Bonded electrons = participate
  • Lone pair = do not participate
  1. The electron pairs occupy the positions such as to minimize repulsions
  2. The valence shell is taken as sphere in which the surrounding atoms takes places as far as possible from each other.
  3. The repulsions are between bond pair –bond pair, lone pair –lone pair and also bond pair –lone pair.
  • The magnitude is: L.P-L. P>L, P-B. P>B.P-B. P
  • The repulsive forces decrease as distance between bonded atoms increase therefore bond angle increases.


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