Among the following, the molecule with the highest dipole moment is:(a) CH3Cl(b) CH2CL2(c) CHCl3(d) CCl4

(a) NOTE: 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 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 by the introduction of the third Cl – atom. When the fourth Cl – atom is introduced, the , molecule (CCl₄) again becomes symmetrical and dipole moment reduces to zero. So, CH₃Cl will have the maximum dipole moment.