Q. 12 The boiling point of halogens from 𝐅𝟐 to 𝐈𝟐 increases due to
(A) decrease in electron affinity
(B) decrease in ionization potential
(C) dipole-dipole interaction
(D) induced dipole – induced dipole interaction

The boiling point of halogens rises from F₂ (-188°C) to I₂ (184°C) due to increasing molecular size and electron count, strengthening intermolecular forces.​

Correct Answer

(D) induced dipole – induced dipole interaction

Halogen molecules (F₂, Cl₂, Br₂, I₂) are nonpolar diatomic gases. Their boiling points increase down the group because larger molecules like I₂ have more electrons, leading to greater polarizability and stronger induced dipole-induced dipole forces (London dispersion forces). These temporary attractions require more energy to overcome, raising the boiling point.​

Option Explanations

(A) Decrease in Electron Affinity

Electron affinity decreases down the group (F > Cl > Br > I) due to increasing atomic size, making it harder for larger anions to hold extra electrons. However, this trend does not directly affect boiling points of nonpolar molecules, as boiling points depend on intermolecular forces, not electron gain tendencies.​

(B) Decrease in Ionization Potential

Ionization energy decreases from F₂ to I₂ because larger atoms shield outer electrons better from the nucleus. This influences metallic character or reactivity but plays no role in the intermolecular forces determining boiling points of covalent halogens.​

(C) Dipole-Dipole Interaction

Dipole-dipole forces occur between polar molecules with permanent dipoles. Halogens lack significant polarity (symmetric X-X bonds), so these forces are negligible. Permanent dipoles do not explain the trend.​