Question

Which of the following molecules has the highest dipole moment?
A. ${H_2}S$
B. $C{O_2}$
C. $CC{l_4}$
D. $B{F_3}$

Answer 1

Dipole moment occurs only when there is a separation of charge. Dipole moments can occur between two ions in a compound with an ionic bond or between two atoms with a covalent bond. Dipole moment depends upon the distance between the charges. It also depends upon the structure of the compound.

Complete step by step answer:
We are given four compounds and we have to determine the compound with the highest dipole moment.
$C{O_2}$ is called carbon dioxide. In $C{O_2}$ molecule, two oxygen atoms form a bond with the carbon atom. There are two carbon-oxygen double bonds in $C{O_2}$, $O = C = O$ . The structure of $C{O_2}$ is linear and symmetrical. Therefore, the dipole moment of one carbon-oxygen double bond gets canceled with the dipole moment of another carbon-oxygen double bond because of the opposite directions. So the net dipole moment is zero.

$CC{l_4}$ is carbon tetrachloride. In $CC{l_4}$, the chlorine atoms are positioned around the carbon atom. The chlorine atoms are put in the corners in tetrahedral configuration symmetrically. The net dipole moment thus becomes zero.

In $B{F_3}$, the fluorine atoms are positioned around boron with boron-fluorine single bonds. The angle between two consecutive bonds is 120 degrees. So the net dipole moment of the three bonds becomes zero.

Therefore, ${H_2}S$ has the highest dipole moment.

The correct option is Option A.

Note:
The bond angle in a linear molecule is 180 degrees, in a symmetrical tetrahedral molecule it is 90 degrees and in planar molecules, it is 120 degrees. The dipole moment is a vector quantity, therefore it has a direction. So in a linear molecule if one dipole moment is positive then the other will be negative thus the net dipole moment is zero.