Valence Bond Theory :- Point-wise explaination , Limitations

Valence Bond Theory is about formation of covalent bond between atoms on the condition that they have hald-filled valence atomic orbitals .

Valence Bond Theory was introduced by two american scientists : Linus Pauling and John C. Slator in the year 1928 . 

Valence Bond Theory (VBT) can be understand by the following points or we say that following are the points of V.B.T. :-

1. Covalent bond between atoms is formed by the overlapping of atomic orbitals .
2. Only the half-filled orbitals which have electrons of opposite spin are able to take part in overlapping .
3. On the extend of overlapping , strength of bond also increases i.e. extend of overlapping decides strength of bond and therefore the bond energy is also higher .
4. On increasing in bond strength , the bond length decreases . This gives a relation that in the formation of covalent bond , the Bond strength is inversely proportional to its bond length .
5. The overlapping of atomic orbitals are possible in two ways which are :

a. Axial Overlapping : Horizontal atomic orbitals overlaps and the bond formed from this overlapping is Sigma Bond .
b. Parallel Overlapping : Parallel atomic orbitals overlaps and the bond formed from this is π Bond .

  

Example :- Formation of Hydrogen Molecule .

This was all about Valence Bond Theory .

But Valence Bond Theory (VBT) was not perfectly right . There were some limitations too in this theory . So , now we will discuss about the limitations of VBT .

Limitations of Valence Bond Theory

1. It fails to explain the tetravelency of carbon .

2. This theory doesn't discuss a bit the energies of electrons .

3. The assumptions are about the electrons being localised to specific locations . etc.

• This was all about Valence Bond Theory which is useful to exam preparations .

• You can also use it as quick notes for exams .

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