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what are the limitations of valence bond theory?

Limitation of Valence Bond Theory

  • Lots of assumption are involved
  • Colour exhibition by coordination compounds is not explained.
  • For a compound of coordination number 4 is tetrahedral or square planar cannot be exactly predicted.
  • Weak and strong ligands cannot be distinguished.
  • It cannot explain why certain ligands form high spin and while others low spin complexes.

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 The valence bond theory was fairly successful in explaining qualitatively the geometry and magnetic behaviour of the complexes. But, it could not explain the following :

(i) The origin of their absorption spectra could not be explained.

(ii) Why did different complexes of the same metal show different colours.

(iii) Relative stabilities of different complexes could not be explained.

(iv) Why should certain ligands form high spin, while others low spin complexes.

(v) it assumes all bonds are localized bonds. As we will see, this is not a valid assumption.

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