Question

Consider the given species: H\(_2\)S, H\(_2\)O, NH\(_3\), NF\(_3\), CHCl\(_3\) The number of lone pairs on the central atom which has the lowest dipole moment is:

• A. 0
• B. 1
• C. 2
• D. 3

Hint:

Symmetry plays a crucial role in determining dipole moments. A lone pair on the central atom may have little or no effect on the dipole moment if the geometry is symmetric enough.

Answer 1

The Correct Option is B

Step 1: Dipole moment and lone pairs.
A molecule’s dipole moment depends on the electronegativity difference between atoms and the symmetry of the molecule. Molecules with lone pairs on the central atom typically have dipole moments, unless the geometry cancels it out. Step 2: Analyze the species.
- H\(_2\)S has 2 lone pairs on the sulfur atom and a significant dipole moment. - H\(_2\)O has 2 lone pairs on the oxygen atom, contributing to its dipole moment. - NH\(_3\) has 1 lone pair on nitrogen, and it has a dipole moment. - NF\(_3\) has 1 lone pair on nitrogen, but due to the symmetry of the molecule, the dipole moment is almost canceled out, making it have a low dipole moment. - CHCl\(_3\) has 1 lone pair on carbon, but the symmetry of the molecule gives it a dipole moment. Step 3: Conclusion.
The molecule with the lowest dipole moment is NF\(_3\) because its lone pair cancels out its dipole due to its trigonal pyramidal geometry. Final Answer: \[ \boxed{1}. \]