Question

Which of the following molecules will show a dipole moment?
(A) Methane
(B) Carbon tetrachloride
(C) Chloroform
(D) Carbon dioxide

Answer 1

Hint: A dipole moment arises due to the electronegativity difference between the two atoms of a bond. Both the ionic and polar covalent bonds can have a dipole moment. It is a vector quantity. The symbols used to represent the charges on the two elements are $\delta +$and$\delta -$, where more electronegative elements get $\delta -$ charge and less electronegative elements get $\delta +$ charge. If a molecule contains more than two atoms, then the net dipole moment is given by the vector sum of all the dipoles in the molecule.

Complete Step by Step Answer:
All the given atoms are polyatomic molecules, that is, they contain more than two atoms. Chloroform ($CHC{{l}_{3}}$) contains three chlorine atoms and one hydrogen atom attached to a single carbon atom. Therefore, it is polarised and shows a dipole moment. Its geometry is tetrahedral. The dipole moment of the $C-H$ bond and the $C-Cl$ bond is in the opposite direction.

Hence, among the given molecules, chloroform will show dipole moment. The dipole moment of chloroform is 1.03 D.
Correct Option: (C) Chloroform.

Note: In methane ($C{{H}_{4}}$), the electronegativity difference between $C$ and $H$ is very small, such that it forms a nonpolar covalent bond. Carbon tetrachloride ($CC{{l}_{4}}$) contains 4 chlorine atoms, each 2 in opposite directions. This will cancel the dipole moments in the opposite direction. Hence, it will have no dipole moment. Similarly, carbon dioxide ($C{{O}_{2}}$) has 2 oxygen atoms in opposite directions of carbon. This will cancel the dipole moment of the 2 carbon-oxygen double bonds. Hence, it will have no dipole moment.