Although fluorine and chlorine are both Group 17 halogens, hydrogen fluoride (HF) exhibits… — JAMB UTME

Although fluorine and chlorine are both Group 17 halogens, hydrogen fluoride ( $HF$ ) exhibits intermolecular hydrogen bonding in the liquid state while hydrogen chloride ( $HCl$ ) does not. Which of the following statements best accounts for this difference?

Fluorine has a higher electronegativity and smaller atomic radius than chlorine, creating a highly polar $H-F$ bond.Answer
B
The intramolecular covalent bond in an $HF$ molecule is weaker than the covalent bond in an $HCl$ molecule.
C
Hydrogen fluoride has a greater molar mass than hydrogen chloride, generating stronger dispersion forces.
D
Chlorine is more electronegative than fluorine, causing $HCl$ molecules to experience non-polar interactions.

Answer

Fluorine's high electronegativity combined with its small atomic size allows for strong electrostatic attraction between the hydrogen atom of one molecule and the lone pair on the fluorine atom of an adjacent molecule.

Hydrogen bonding requires hydrogen to be covalently attached to a very small, highly electronegative atom (N, O, or F). Fluorine fulfills both conditions, giving the

H-F

bond a large dipole moment and high localized charge density that attracts adjacent

HF

molecules strongly.

Step-by-Step Solution

Identify the structural requirements for hydrogen bonding.

Hydrogen bonding occurs specifically when hydrogen is bonded directly to small, highly electronegative atoms (N, O, or F).

High electronegativity creates a strong dipole with high positive charge density on the hydrogen atom.

Compare fluorine and chlorine properties.

Fluorine has an electronegativity of 4.0 and a small atomic radius, whereas chlorine has an electronegativity of 3.0 and a larger atomic radius.

Although chlorine is electronegative, its larger atomic volume diffuses electron charge density, preventing effective hydrogen bond formation.

Select the statement that correctly attributes hydrogen bond formation to electronegativity and atomic size.

The statement emphasizing fluorine's higher electronegativity and smaller atomic size relative to chlorine provides the correct rationale.

It fulfills the fundamental chemical criteria required for hydrogen bond formation.

Key Concept

Intermolecular Forces and Hydrogen Bonding

Estimated Time:1m 0s

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