What is the use of Valence bond theory?

Valence bond theory helps to know about the shape of the molecule.

What is the Valence bond theory?

According to the valence bond theory, electrons in a molecule occupy atomic orbitals rather than molecular orbitals. The atomic orbitals overlap on the bond formation, and the larger the overlap, the stronger the bond.

The important postulates of the valence bond theory are listed below.

  1. Covalent bonds are formed when two valence orbitals (half-filled) belonging to two different atoms overlap. The electron density in the area between the two bonding atoms increases due to this overlapping, thereby increasing the stability of the resulting molecule.
  2. The presence of many unpaired electrons in the valence shell of an atom enables it to form multiple bonds with other atoms. However, the paired electrons present in the valence shell do not participate in the formation of chemical bonds as per the valence bond theory.
  3. Covalent chemical bonds are directional and parallel to the region corresponding to the atomic orbitals that overlap.
  4. Sigma bonds and pi bonds differ in the pattern that the atomic orbitals overlap in, i.e. pi bonds are formed from sidewise overlapping. In contrast, the overlapping along the axis containing the nuclei of the two atoms leads to the formation of sigma bonds.

Application of VBT

  • It helps to describe the covalent bond creation in many molecules
  • The covalent bond in an HF molecule is formed from the overlap of the 1s orbital of the hydrogen atom and a 2p orbital belonging to the fluorine atom, explained by the valence bond theory.

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