Question

substance normal boiling point hf 293 k f₂ 85 k the electron cloud of hf is smaller than that of f₂, however, hf has a much higher boiling point than f₂ has. which of the following explains how the dispersion - force model of intermolecular attraction does not account for the unusually high boiling point of hf? a f₂ is soluble in water, whereas hf is insoluble in water. b the f₂ molecule has a greater mass than the hf molecule has. c liquid f₂ has weak dispersion force attractions between its molecules, whereas liquid hf has strong ionic interactions between h⁺ and f⁻ ions. d liquid f₂ has weak dispersion force attractions between its molecules, whereas liquid hf has both weak dispersion force attractions and hydrogen bonding interactions between its molecules.

Explanation:

Dispersion forces are based on temporary - induced dipoles. $F_2$ is a non - polar molecule with only weak dispersion forces. HF is a polar molecule and in addition to dispersion forces, it has hydrogen bonding (a strong intermolecular force) due to the highly electronegative F atom bonded to H. Solubility in water (A) is not related to the inability of dispersion forces to explain HF's high boiling point. Mass (B) is not the key factor here as intermolecular forces determine boiling point. HF is a covalent compound and does not have strong ionic interactions in the liquid state (C).

Answer:

D. Liquid $F_2$ has weak dispersion force attractions between its molecules, whereas liquid HF has both weak dispersion force attractions and hydrogen bonding interactions between its molecules.