Question

Which of the following molecules does not possess a permanent dipole moment :
(A) $ {{H}_{2}}S$
(B) $ S{{O}_{2}}$
(C) $ C{{S}_{2}}$
(D) $ S{{O}_{3}}$

Answer 1

Hint: A dipole moment is a measure of the electronegativity difference between the two atoms of a bond. In a polyatomic molecule, there are more than one dipole in a molecule .Therefore, the net dipole moment is the vector sum of all the dipoles in the molecule.

Complete Step by Step Answer:
(A) $ {{H}_{2}}S$ - This molecule contains two dipoles from hydrogen to sulphur. It has bent structure. The two dipoles add up to give a non-zero net dipole moment. It has a dipole moment of 0.95 D.

(B) $ S{{O}_{2}}$ - It contains two $ S-O$ double bonds. Due to a lone pair of electrons on sulphur, it has a bent structure. It thus has a non-zero dipole moment. It possess a dipole moment of 1.62 D.

(C) $ C{{S}_{2}}$ - It is a linear molecule, where the two $ C-S$ double bonds are at an angle of $ {{180}^{o}}$ to each other. The two dipoles from carbon to sulphur are equal and opposite and thus cancel out each other’s effect. Hence, this molecule does not possess a permanent dipole moment.

(D) $ S{{O}_{3}}$ - This molecule has three $ S-O$ double bonds at an angle of $ {{120}^{o}}$ . It has trigonal planar geometry. Two of the dipoles cancel out the effect of the third dipole, resulting in a zero dipole moment. Hence, it does not possess a permanent dipole moment.
Correct Option: (C) $ C{{S}_{2}}$ and (D) $ S{{O}_{3}}$.

Note: The dipole moment is a vector quantity, that is, it has both magnitude and direction. Therefore, the direction of dipoles should also be observed while calculating the dipole moment. The direction of the dipole is from more a electronegative atom to a less electronegative atom.