Explain Valance Bond Theory

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Valence Bond Theory

  • In a molecule, electrons inhabit atomic orbitals rather than molecular orbitals.
  • It is based on the concept of bond overlapping.
  • Covalent bonding is a chemical link generated by the sharing of electrons.


  • When two valence orbitals present in two separate atoms overlap on one other, the covalent bonds are created.
  • Due to this overlapping, the electron density between the two bonding atoms increases, increasing the stability of the resulting molecule.
  • The valence shell of an atom has several unpaired electrons, allowing it to make many bonds with other atoms.
  • According to the VBT, the paired electrons present in the valence shell do not participate in the creation of chemical bonds.

Geometry of water molecule:

  • The electronic configuration of the Hydrogen atom is 1s1 and oxygen is 1s22s22p4.
  • In water molecules, there are 2 oxygen atoms, and hence two half-filled p-orbitals.
  • Oxygen needs two more electrons to complete the octet and Hydrogen requires one more electron to acquire the configuration of He.
  • Two-half-filled orbitals of the two Hydrogen atoms separately overlap with one of the two half-filled p-orbitals of the Oxygen atom.
  • This gives rise to two single covalent bonds between the central atom and two Hydrogen atoms.
  • The three p-orbitals are along the three perpendicular axes in space.
  • The valence bond theory of the water molecule describes the two O-H bonds as resulting from the overlap of 1s orbital of Hydrogen with the two half-filled 2p orbitals of the oxygen atom.
  • Since the two 2p orbitals are at right angles to one another, valence bond theory predicts a bent geometry for the water molecule with a bond angle of 90°.
  • The H-O-H bond angle in water is 104.45°and is having a bent tetrahedral geometry or V-shaped.
  • The opening of the angle to a value greater than the predicted one of 90°can be accounted as due to the repulsion between the two hydrogen nuclei.

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