Q14 / 180 · COMEDK 2022 · Chemistry
Which of the following molecules does not exhibit dipole moment?
(i) $\mathrm{CCl}_4$
(ii) $\mathrm{CO}_2$
(iii) $\mathrm{NH}_3$
(iv) $\mathrm{CHCl}_3$
(v) $\mathrm{H}_2 \mathrm{O}$
(vi) $\mathrm{CH}_3-\mathrm{O}-\mathrm{CH}_3$
- A(ii), (v), (iv)
- B(i), (iii), (vi)
- Correct answerC(i), (ii)
- D(iii), (iv), (vi)
Solution
A molecule exhibits a net dipole moment if the vector sum of the individual bond dipoles is non-zero. This depends on the molecular geometry and the electronegativity difference between atoms.
$\mathrm{CCl}_4$ has a tetrahedral geometry. The four $\mathrm{C-Cl}$ bond dipoles are equal in magnitude and directed towards the corners of a regular tetrahedron, resulting in a net dipole moment of zero.
$\mathrm{CO}_2$ has a linear geometry ($O=C=O$). The two $\mathrm{C=O}$ bond dipoles are equal and opposite, cancelling each other out, resulting in a net dipole moment of zero.
$\mathrm{NH}_3$ has a trigonal pyramidal geometry with a lone pair on nitrogen. The bond dipoles do not cancel, leading to a non-zero dipole moment.
$\mathrm{CHCl}_3$ has a tetrahedral geometry, but the bond dipoles of $\mathrm{C-H}$ and $\mathrm{C-Cl}$ are different, resulting in a non-zero net dipole moment.
$\mathrm{H}_2 \mathrm{O}$ has a bent geometry due to two lone pairs on oxygen, resulting in a non-zero net dipole moment.
$\mathrm{CH}_3-\mathrm{O}-\mathrm{CH}_3$ (dimethyl ether) has a bent geometry around the oxygen atom, resulting in a non-zero net dipole moment.
Therefore, only $\mathrm{CCl}_4$ and $\mathrm{CO}_2$ have a net dipole moment of zero.
Answer: (i), (ii)
$\mathrm{CCl}_4$ has a tetrahedral geometry. The four $\mathrm{C-Cl}$ bond dipoles are equal in magnitude and directed towards the corners of a regular tetrahedron, resulting in a net dipole moment of zero.
$\mathrm{CO}_2$ has a linear geometry ($O=C=O$). The two $\mathrm{C=O}$ bond dipoles are equal and opposite, cancelling each other out, resulting in a net dipole moment of zero.
$\mathrm{NH}_3$ has a trigonal pyramidal geometry with a lone pair on nitrogen. The bond dipoles do not cancel, leading to a non-zero dipole moment.
$\mathrm{CHCl}_3$ has a tetrahedral geometry, but the bond dipoles of $\mathrm{C-H}$ and $\mathrm{C-Cl}$ are different, resulting in a non-zero net dipole moment.
$\mathrm{H}_2 \mathrm{O}$ has a bent geometry due to two lone pairs on oxygen, resulting in a non-zero net dipole moment.
$\mathrm{CH}_3-\mathrm{O}-\mathrm{CH}_3$ (dimethyl ether) has a bent geometry around the oxygen atom, resulting in a non-zero net dipole moment.
Therefore, only $\mathrm{CCl}_4$ and $\mathrm{CO}_2$ have a net dipole moment of zero.
Answer: (i), (ii)
Hence, the correct answer is option: 'C'.