Question

Identify the molecule having a non-zero dipole moment.

• A. $\text{BF}_3$
• B. $\text{CCl}_4$
• C. $\text{CHCl}_3$
• D. $\text{CH}_4$

Hint:

Any compound possessing a perfectly symmetrical basic geometric shape ($\text{AX}_2$ linear, $\text{AX}_3$ trigonal planar, $\text{AX}_4$ tetrahedral) will always have a dipole moment of zero if and only if all surrounding $X$ atoms are completely identical. If you change even one single atom (like switching $\text{CCl}_4$ to $\text{CHCl}_3$), the symmetry shatters and the molecule becomes polar!

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The problem requires us to examine four covalent molecules and identify the single compound that behaves as a polar molecule with a net permanent dipole moment ($\mu \neq 0$).

Step 2: Key Formula or Approach:
The net molecular dipole moment is the vector sum of all individual bond dipole moments within the molecule's specific three-dimensional geometry: $$\vec{\mu}_{\text{net}} = \sum \vec{\mu}_{\text{bond}}$$ Highly symmetrical geometries containing identical peripheral atoms result in a perfect vector cancellation, rendering the overall molecule non-polar ($\mu = 0$).

Step 3: Detailed Explanation:
Let's systematically evaluate the spatial symmetry of each option:

$\text{BF}_3$ (Boron trifluoride): Possesses a highly symmetrical trigonal planar geometry. The three polar B-F bond vectors pull at equal $120^\circ$ angles in a single plane, canceling each other out perfectly ($\mu = 0$).

$\text{CH}_4$ (Methane) and $\text{CCl}_4$ (Carbon tetrachloride): Both display a perfectly symmetrical tetrahedral geometry. Because all four peripheral atoms are identical (H or Cl), the individual bond dipoles completely cancel out in three dimensions ($\mu = 0$).

$\text{CHCl}_3$ (Chloroform): While it is also based on a tetrahedral framework, the symmetry is broken because the top hydrogen atom is structurally different from the three heavy chlorine atoms. The individual bond dipoles of the three highly polar C-Cl bonds combine constructively with the dipole of the C-H bond, creating a strong net downward molecular dipole moment ($\mu \neq 0$).

Step 4: Final Answer:
The molecule with a net dipole moment is $\text{CHCl}_3$, which maps to option (C).