Question

Which of the following has the highest dipole moment?

• A. $C{H}_{3}Cl$
• B. $C{H}_{2}C{l}_2$
• C. $CHC{l}_3$
• D. $CC{l}_4$

Answer 1

The correct option is A $C{H}_{3}Cl$

Dipole moment is a vector quantity.
Methane molecule being symmetrical, has zero dipole moment. Replacement of one of the $H$- atoms by $Cl$ atom increases the dipole moment. The increase in dipole moment is rather more than what can be expected because of the fact that the bond dipole moment of $C-H$ bond and that of $C-Cl$ bond reinforce one another.
Replacement of another $H$ atom by $Cl$ increases the bond angle due to lone pair - lone pair repulsion between two $Cl$-atoms thereby reducing the dipole moment of the molecule. Increase in angle is again caused by the the introduction of the third $Cl$-atom. When the fourth $Cl$-atom is introduced, the molecule $\left(CC{l}_4\right)$again becomes symmetrical and dipole moment reduces to zero. So, $\left(C{H}_{3}Cl\right)$ will have the maximum dipole moment.