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Difficulty: HardIntermolecular Forces and Hydrogen Bonding

Arrange the following chemical substances in order of increasing boiling point, starting from the substance with the lowest boiling point to the one with the highest boiling point based on the nature and relative strength of their intermolecular forces.

  1. 1Methane (CH4CH_4)
  2. 2Hydrogen sulfide (H2SH_2S)
  3. 3Ammonia (NH3NH_3)
  4. 4Water (H2OH_2O)

Answer

The correct order of increasing boiling point is Methane (CH4CH_4) < Hydrogen sulfide (H2SH_2S) < Ammonia (NH3NH_3) < Water (H2OH_2O).
The sequence reflects the increasing magnitude of intermolecular forces: non-polar Methane (CH4CH_4) relies solely on weak London dispersion forces (lowest boiling point). Polar Hydrogen sulfide (H2SH_2S) has dipole-dipole interactions but lacks hydrogen bonding because sulfur is not electronegative enough. Ammonia (NH3NH_3) undergoes hydrogen bonding due to nitrogen's high electronegativity. Water (H2OH_2O) forms an extensive network of strong hydrogen bonds, resulting in the highest boiling point.

Step-by-Step Solution

1
Identify the type of intermolecular forces operating in each substance
CH4CH_4 is non-polar (London dispersion forces only); H2SH_2S is polar (dipole-dipole and dispersion forces); NH3NH_3 is polar with hydrogen bonding; H2OH_2O is polar with strong, extensive hydrogen bonding.
Boiling point depends directly on the total magnitude of attraction between molecules in the liquid state.
2
Compare non-hydrogen-bonding substances (CH4CH_4 vs H2SH_2S)
CH4CH_4 has the weakest intermolecular forces (dispersion only), while H2SH_2S has additional permanent dipole-dipole attractions.
Permanent dipole-dipole interactions in polar molecules generally create stronger attraction than non-polar dispersion forces of comparable size.
3
Compare hydrogen-bonding substances (NH3NH_3 vs H2OH_2O)
Both NH3NH_3 and H2OH_2O form hydrogen bonds, but H2OH_2O forms up to four hydrogen bonds per molecule in a 3D network, whereas NH3NH_3 is limited by its single lone pair to fewer hydrogen bonds per molecule.
Oxygen is more electronegative than nitrogen, and water has an optimal 1:1 ratio of lone pairs to hydrogen atoms for maximum hydrogen-bonding capacity.
4
Synthesize the complete sequence from lowest to highest boiling point
CH4CH_4 < H2SH_2S < NH3NH_3 < H2OH_2O
Intermolecular attraction strength increases in the order: London dispersion forces < dipole-dipole interactions < moderate hydrogen bonding < extensive hydrogen bonding.

Key Concept

Relative strengths of intermolecular forces (London dispersion, dipole-dipole, and hydrogen bonding) and their effect on physical properties like boiling point.
Estimated Time:2m 0s
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Topics

Intermolecular Forces and Hydrogen Bonding

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