Jun 272013

Chemistry is a vast subject. This is the branch of science that deals with the study of different chemicals, elements, compounds etc. We can find huge number of laws, theories and hypothesis in this subject. Some of them are Dalton’s Atomic Theory, Hund’s rule, Aufbau Principle etc. Among them, VSEPR theory is also the one. This is the theory which was brought out by Sidwick and Powell in order to predict the shapes of the molecules theoretically. The full form of VSEPR is Valence Shell Electron Pair Repulsion.

This theory is based on the fact that electron pairs in valence shell of an atom try to remain as far apart as possible so as to have minimum repulsion between them and the molecules take the shape on the basis of the number and nature of electron pair in the valence shell. The basic assumptions of VSEPR theory are:

  • A covalent molecule consists of a central atom to which other atoms are attached.
  • The valence shell of central atom consists of electrons in pair which may be bond pair or lone pair.
  • The repulsion between the electron pairs decreases in the order given below:
    lone pair-lone pair > lone pair-bond pair > bond pair-bond pair
  • The molecules take the shape so that there is minimum repulsion between the electron pairs.
  • The molecules with the central atom containing only the bond pairs in the valence shell have regular geometry while the molecules with the central atom containing the lone pairs will have irregular or distorted shape.