Although both CO 2 and H 2 O are triatomic molecules, the shape of H2O molecule is bent while that of CO 2 is linear. Explain this on the basis of dipole moment.

Question

Philoid · Accepted Answer

A diatomic molecule is polar if the bond formed between the atoms is polar. In such a molecule, the dipole moment of the bond gives the dipole moment of the molecule. For example, the dipole moment of HCl molecule is the same as the dipole moment of HCl bond.

However, in the case of molecules containing more than two atoms, the dipole moment not only depends upon the individual dipole moments but also on the spatial arrangement of various bonds in the molecule.

Carbon dioxide (CO₂) and water (H₂O) molecules are both triatomic molecules. It has been experimentally observed that dipole moment of CO₂ is zero and dipole moment of H₂O is 1.85D

If the dipole moment is zero, it is only possible when the molecule is linear so that the dipole moment of C=O bond on one side of the molecule is cancelled by that on the other side of the molecule giving net zero dipole moment.

μ = 0, shape is linear

If the dipole moment of H₂O is 1.85D, which shows that the molecule is non- linear. The H₂O molecule is bent, which is only possible when the dipole moment of the two O—H bonds inclined at an angle of 104.5^° and the contribution of electrons of the two lone pairs of electrons on the oxygen atom.

μ = 1.85D, shape is bent

Although both CO2 and H2O are triatomic molecules, the shape of H2O molecule is bent while that of CO2 is linear. Explain this on the basis of dipole moment.

Although both CO₂ and H₂O are triatomic molecules, the shape of H2O molecule is bent while that of CO₂ is linear. Explain this on the basis of dipole moment.