Which molecule in each pair has the greater dipole moment? Give the reason for your choice. (a) ClO2 or SO2 (b) HBr or HCl (c) BeCl2 or SCl2 (d) AsF3 or AsF5
The Correct Answer and Explanation is:
To determine which molecule in each pair has the greater dipole moment, we must examine factors such as molecular shape, electronegativity differences, and symmetry. Here’s the breakdown for each pair:
(a) ClO₂ vs SO₂
- Answer: SO₂ has the greater dipole moment.
- Explanation:
Both molecules are bent, but SO₂ has a higher electronegativity difference between sulfur and oxygen (S-O bond) than ClO₂ does (Cl-O bond). Additionally, sulfur has a higher charge distribution due to its larger size, resulting in a stronger dipole. Although chlorine is more electronegative than sulfur, the Cl-O bond is less polar, and chlorine’s larger atomic radius reduces the overall dipole moment. Therefore, SO₂ has a greater dipole moment because the sulfur-oxygen bonds contribute more to the polarity of the molecule than chlorine-oxygen bonds.
(b) HBr vs HCl
- Answer: HCl has the greater dipole moment.
- Explanation:
Both HBr and HCl are polar molecules due to the difference in electronegativity between hydrogen and the halogens. However, chlorine is more electronegative than bromine, meaning the H-Cl bond is more polar than the H-Br bond. Since the dipole moment depends on both the bond polarity and the distance between the nuclei, HCl has a larger dipole moment due to the greater electronegativity difference between hydrogen and chlorine.
(c) BeCl₂ vs SCl₂
- Answer: SCl₂ has the greater dipole moment.
- Explanation:
BeCl₂ is a linear molecule with symmetrical charge distribution, which means its dipole moments cancel each other out. In contrast, SCl₂ is bent, and its molecular shape doesn’t allow the dipoles to cancel out. This results in a net dipole moment for SCl₂. Moreover, sulfur is more electronegative than beryllium, contributing to a larger dipole moment in SCl₂.
(d) AsF₃ vs AsF₅
- Answer: AsF₃ has the greater dipole moment.
- Explanation:
AsF₃ has a trigonal pyramidal structure, which is asymmetrical, so the dipoles do not cancel out. In contrast, AsF₅ has a trigonal bipyramidal shape, which is symmetrical, meaning the dipoles cancel out and the molecule has no net dipole moment. Even though fluorine is highly electronegative, the symmetry of AsF₅ results in a dipole moment of zero, while the asymmetry of AsF₃ ensures a non-zero dipole moment.
In summary:
- SO₂ > ClO₂
- HCl > HBr
- SCl₂ > BeCl₂
- AsF₃ > AsF₅
