Arrange the following molecules in order of increasing dipole moment:
H2O
H2S
CBr4
NH3
CO2
HF
The correct answer and explanation is :
The correct order of increasing dipole moment is:
CBr₄ < CO₂ < H₂S < NH₃ < H₂O < HF
Explanation:
The dipole moment ((\mu)) of a molecule depends on:
- Electronegativity Difference: The greater the difference in electronegativity between atoms, the larger the dipole moment.
- Molecular Geometry: The shape of the molecule determines whether individual bond dipoles cancel out or add up to create a net dipole.
Analysis of Each Molecule:
- CBr₄ (Carbon Tetrabromide) – μ = 0 D
- Reason: It has a tetrahedral structure with four C–Br bonds that are symmetrically arranged. The individual bond dipoles cancel out, making it a nonpolar molecule with zero dipole moment.
- CO₂ (Carbon Dioxide) – μ = 0 D
- Reason: It has a linear structure, and the two polar C=O bonds cancel each other out, making CO₂ a nonpolar molecule.
- H₂S (Hydrogen Sulfide) – μ ≈ 0.95 D
- Reason: H₂S is bent like H₂O, but sulfur is less electronegative than oxygen (O = 3.5, S = 2.5), so its dipole moment is smaller than that of H₂O.
- NH₃ (Ammonia) – μ ≈ 1.47 D
- Reason: NH₃ has a trigonal pyramidal structure due to lone pair repulsion. The N-H bonds do not cancel out, resulting in a net dipole.
- H₂O (Water) – μ ≈ 1.85 D
- Reason: H₂O has a bent shape and a large electronegativity difference (O = 3.5, H = 2.1), leading to a higher dipole moment than NH₃.
- HF (Hydrogen Fluoride) – μ ≈ 1.91 D
- Reason: HF has the largest electronegativity difference (F = 4.0, H = 2.1), resulting in the highest dipole moment among these molecules.