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Difficulty: MediumIntermolecular Forces and Hydrogen Bonding

Arrange the following hydrogen halides in order of increasing boiling point, starting from the compound with the lowest boiling point to the compound with the highest boiling point.

  1. 1Hydrogen chloride (HClHCl)
  2. 2Hydrogen bromide (HBrHBr)
  3. 3Hydrogen iodide (HIHI)
  4. 4Hydrogen fluoride (HFHF)

Answer

The correct sequence in order of increasing boiling point is Hydrogen chloride (HClHCl), Hydrogen bromide (HBrHBr), Hydrogen iodide (HIHI), and Hydrogen fluoride (HFHF).
The correct sequence ranks the Group 17 hydrides by increasing boiling point: HCl<HBr<HI<HFHCl < HBr < HI < HF. For HClHCl, HBrHBr, and HIHI, boiling points rise systematically with increasing atomic size and molar mass because larger electron clouds enhance polarizability and London dispersion forces. HFHF breaks this trend and has the highest boiling point in the group due to the presence of strong intermolecular hydrogen bonding.

Step-by-Step Solution

1
Identify the primary intermolecular forces present in each hydrogen halide.
HClHCl, HBrHBr, and HIHI interact mainly via London dispersion forces and dipole-dipole interactions, while HFHF forms strong intermolecular hydrogen bonds.
Fluorine is extremely small and electronegative, fulfilling the requirements for hydrogen bonding.
2
Compare van der Waals forces among HClHCl, HBrHBr, and HIHI.
Boiling point increases progressively from HClHCl to HBrHBr to HIHI.
As molecular size and electron cloud volume increase down Group 17, polarizability increases, leading to stronger temporary dipoles and stronger London dispersion forces.
3
Determine the position of HFHF within the series.
HFHF has an anomalously high boiling point compared to the rest of the group.
Intermolecular hydrogen bonding is considerably stronger than van der Waals dispersion forces, making HFHF the least volatile of the four hydrogen halides.

Key Concept

Boiling point trends in hydrides are governed by the interplay of London dispersion forces (which scale with molar mass and polarizability) and hydrogen bonding.
Estimated Time:1m 0s
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Topics

Intermolecular Forces and Hydrogen Bonding

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