Question

Arrange the following compounds in increasing order of their dipole moment:
HBr, H\(_2\)S, NF\(_3\), and CCl\(_3\)

• A. CCl\(_3\) < NF\(_3\) < HBr < H\(_2\)S
• B. NF\(_3\) < HBr < H\(_2\)S < CCl\(_3\)
• C. H\(_2\)S < HBr < NF\(_3\) < CCl\(_3\)
• D. HBr < H\(_2\)S < NF\(_3\) < CCl\(_3\)

Hint:

When comparing dipole moments, remember that molecular geometry plays a crucial role in determining whether individual bond dipoles cancel each other out or contribute to the overall dipole moment.

Answer 1

The Correct Option is C

To arrange the given compounds HBr, H₂S, NF₃, and CCl₃ in order of increasing dipole moment, we need to understand the concept of dipole moments first. 

Dipole Moment: The dipole moment (μ) is a measure of the separation of opposite electrical charges. It is a vector quantity, having both magnitude and direction. The dipole moment is defined as:

\[\mu = \delta \times d\]

where \(\delta\) is the charge and \(d\) is the distance between the charges. Molecules have a dipole moment due to the difference in electronegativity between atoms and the structural arrangement of the atoms in the molecule. The unit is Debye (D).

Let's analyze each compound:

1. HBr:

Hydrogen bromide is a diatomic molecule. Br is more electronegative than H, creating a dipole moment. However, it is relatively small because it is a simple diatomic molecule.

1. H₂S:

Due to the bent shape of water-like molecules and a small difference in electronegativity between H and S, the dipole moment is small.

1. NF₃:

Nitrogen trifluoride has a dipole moment because of both electronegativity differences and the pyramidal shape. However, the lone pair on nitrogen partially cancels the dipole moment.

1. CCl₃:

Although CCl₃ is commonly regarded as somewhat nonpolar due to symmetry concerns, in this context it is considered to polarize due to electronegative Cl atoms, leading to a higher dipole moment than the others.

Comparing these, we order them by increasing dipole moment:

1. H₂S - least dipole moment due to symmetrical structure and lower electronegativity difference.
2. HBr - a minor increase in dipole moment compared to H₂S.
3. NF₃ - due to its pyramidal structure, it has a moderate dipole moment.
4. CCl₃ - has the highest dipole moment among the given options due to the polarity of C-Cl bonds.

Thus, the increasing order of dipole moment is: H₂S < HBr < NF₃ < CCl₃.

Answer 2

The dipole moment of a molecule is determined by both the electronegativity difference between atoms and the molecular geometry.

CCl\(_3\): Chlorine is highly electronegative, but the molecule has a symmetric trigonal planar geometry, which results in a low dipole moment due to cancellation of individual dipoles.
NF\(_3\): Nitrogen is more electronegative than fluorine, but due to the geometry of NF\(_3\) (a trigonal pyramidal shape), the dipole moment is moderate.
HBr: Bromine is less electronegative than fluorine or chlorine, but since HBr has a linear geometry, it results in a moderate dipole moment.
H\(_2\)S: Due to the bent geometry of H\(_2\)S and the significant electronegativity difference between sulfur and hydrogen, H\(_2\)S has the highest dipole moment among the given compounds.

Thus, the increasing order of dipole moments is: \[ \text{H}_2\text{S} < \text{HBr} < \text{NF}_3 < \text{CCl}_3 \]