Question

Which of the following has the highest dipole moment?
A.$B{{F}_{3}}$
B.$C{{O}_{2}}$
C.$CC{{l}_{4}}$
D.$N{{F}_{3}}$

Answer 1

We know that the 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 answer: A dipole moment arises in any system in which there is a separation of charge. They can arise in ionic bonds as well as in covalent bonds. Dipole moments occur due to the difference in electronegativity between two chemically bonded atoms. The measure of the polarity of a chemical bond between two atoms in a molecule is known as the bond dipole moment of that molecule. 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. 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 a molecule, two oxygen atoms form a bond with the carbon atom. There are two carbon-oxygen double bonds in $O=C=O.$ The structure 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.
$N{{F}_{3}}$ has a high dipole moment compared to other compounds because Nitrogen has lone pair electrons. In $B{{F}_{3}},\text{ }CC{{l}_{4}},\text{ }C{{O}_{2}}$ dipole moment is zero.
Therefore, the correct answer is option D.

Note:
Remember that these molecules have tetrahedral geometry due to sp3 hybridization of carbon atoms. We know that for symmetrical compounds the dipole moment is always zero. Hence, they are non-polar. In the case of a single bond in a polyatomic molecule its dipole moment is known as the bond dipole moment and this dipole moment is different from the dipole moment of the whole molecule.