21 Chemistry -- Chemical Bonding and Shapes of Molecules

What does VSEPR theory explain? write its postulates.

What does VSEPR theory explain? write its postulates.

The VSEPR theory explains that the approximate shape of the molecule can be predicted from the number of electron pairs in the valence shell of the central atom. 

The postulates of the VSEPR theory are listed below: 

  • In polyatomic molecules one of the constituent atoms is the central atom to which all other atoms are linked.
  • The total number of valence shell electron pairs (lone pair and bond pair) decides the shape of the molecule.
  • The electron pairs are oriented in a way that electrostatic repulsion between them is minimum.
  • If the central atom is surrounded by bond pairs, then, the asymmetrically shaped (regular)molecule can be expected.
  • If the central atom be surrounded by both lone pairs and bond pairs of electrons, the molecule tends to have a distorted shape. The strength of the repulsion is in order of    l.p--l.p > l.p--b.p. > b.p--b.p
  • The magnitude of repulsion between the bonding pairs of electrons depends on the electronegative difference between the central atom and other atoms. 
  • The repulsion in multiple bonds is in order of: Triple > Double > Single bond. 

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