Consider the following halogen-containing compounds:
The compounds with a net dipole moment are:
Show Hint
To determine whether a compound has a net dipole moment:
1. Consider the molecular geometry and symmetry.
2. Asymmetrical molecules or those with unsymmetrical arrangements of polar bonds typically have a net dipole moment.
Step 1: Understand Dipole Moment and Symmetry
A molecule has a net dipole moment if:
1. The individual bond dipoles do not cancel out due to asymmetry in the molecular structure.
2. The molecule is polar, meaning it has a separation of charge.
Step 2: Analyze Each Compound
I) $ \text{CHCl}_3 $ (Chloroform)
Chloroform has a tetrahedral geometry, but it is asymmetric because three chlorine atoms replace hydrogen atoms on one side of the carbon atom.
This asymmetry results in a net dipole moment.
Has a net dipole moment.
II) $ \text{CCl}_4 $ (Carbon Tetrachloride)
Carbon tetrachloride has a symmetrical tetrahedral geometry.
All four chlorine atoms are identical and symmetrically arranged around the central carbon atom.
The bond dipoles cancel out, resulting in no net dipole moment.
Does not have a net dipole moment.
III) $ \text{CH}_3\text{F} $ (Methyl fluoride)
Methyl fluoride has a trigonal pyramidal geometry due to the lone pair on the fluorine atom.
The molecule is asymmetric, and the C–F bond has a significant dipole moment.
Has a net dipole moment.
IV) $ \text{ClC}_6\text{H}_4\text{Cl} $ (1,2-Dichlorobenzene)
1,2-Dichlorobenzene has a non-symmetrical arrangement of chlorine atoms on adjacent carbons in the benzene ring.
The symmetry of the benzene ring is disrupted, resulting in a net dipole moment.
Has a net dipole moment.
V) $ \text{ClC}_6\text{H}_4\text{Cl} $ (1,4-Dichlorobenzene)
1,4-Dichlorobenzene has chlorine atoms on opposite sides of the benzene ring, maintaining the overall symmetry of the molecule.
The bond dipoles cancel out due to symmetry.
Does not have a net dipole moment. Step 3: Identify the Correct Option
From the analysis:
I ($ \text{CHCl}_3 $): Has a net dipole moment.
II ($ \text{CCl}_4 $): Does not have a net dipole moment.
III ($ \text{CH}_3\text{F} $): Has a net dipole moment.
IV ($ \text{ClC}_6\text{H}_4\text{Cl} $): Has a net dipole moment.
V ($ \text{ClC}_6\text{H}_4\text{Cl} $): Does not have a net dipole moment.
Thus, the compounds with a net dipole moment are I, III, and IV.
Step 4: Match with Options
Option (1): I, IV only
Incorrect — does not include III.
Option (2): II, III, IV only
Incorrect — includes II, which does not have a dipole moment.
Option (3): I, III and IV only
Correct — matches the analysis.
Option (4): III, IV and V only
Incorrect — includes V, which does not have a dipole moment.
