Question

Give any three main postulates of valence bond theory (VBT)

Answer 1

 Hint:The valence bond theory is used for explaining the bond formation in the coordination compound. It explains the bonding using quantum mechanics.

Complete step by step answer:
The three main postulates of the valence bond theory are:
(1)When two valence orbitals of different atoms overlap with each other, a covalent bond forms. In the area between that of the two bonding atoms the electron density due to the overlapping. This makes the resulting molecule stable.
(2)An atom having unpaired electrons in their valence shell can form multiple bonds with other atoms.
(3)The pi bonds occur by the overlapping of the orbitals sidewise and the sigma bonds occur by the overlapping of the orbitals along the axis.

Additional information:
The Valence bond theory also has various limitations. Theses are,
(1) Valence bond theory couldn’t explain the tetravalent property of the carbon atom
(2)Details about the energies of the electrons could not be provided by the valence bond theory.
(3)This theory does not account on the kinetic stability and thermodynamic stability of the coordination compounds
(4)The valence bond theory could not differentiate between the strong ligands and the weak ligands.
(5)The colour exhibited by the coordination compounds is unable to explain by the valence bond theory.

There are various applications of the valence bond theory. The bonding in the HF molecule is portrayed by the valence bond theory. The difference in the strength and length of the bonds in the ${{\rm{F}}_{\rm{2}}}$and the ${{\rm{H}}_{\rm{2}}}$molecule can be explain by considering the orbital overlap.

Note:
The formation of bonds among atoms of a compound is given the Valence bond theory. This theory also predicts the type of hybridization and the geometry of a compound with respect to the coordination number.