Chemistry Chemical Bonding MDCAT 2010
PMDC Verified Question 101 of 102
Which one of the following has zero dipole moment:
A
\( \text{NH}_3 \)
B
\( \text{H}_2\text{O} \)
C
\( \text{CHCl}_3 \)
D
\( \text{BF}_3 \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: \( \text{BF}_3 \)
Concept:

A zero dipole moment requires complete molecular symmetry so that all bond vectors cancel out perfectly.

Formula:

$$ \vec{\mu}_{\text{net}} = \sum \vec{\mu}_{\text{bonds}} $$

Solution:

  • \( \text{BF}_3 \) is a trigonal planar molecule with no lone pairs on the central Boron atom.


  • The pull of the three highly electronegative Fluorine atoms is perfectly balanced in 2D space, making it a non-polar molecule with a zero dipole moment.


Why other options are incorrect:

  • Option A & Option B: Have lone pairs that destroy symmetry.
  • Option C: \( \text{CHCl}_3 \) has tetrahedral geometry, but because the atoms attached to Carbon are not all identical (one H, three Cl's), the bond dipoles do not cancel, leaving a net dipole.

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