Hydrogen Bonding and the Boiling Points of Hydrides
ChemistryChemical BondingAges 15–16
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Chemical Bonding
A graph of the actual boiling points of the hydride series H₂O–H₂S–H₂Se–H₂Te, HF–HCl–HBr–HI, NH₃–PH₃–AsH₃–SbH₃ and CH₄–SiH₄–GeH₄–SnH₄ against period. Students switch each series on or off and tap a point to see a molecular model: H₂O, HF and NH₃ have hydrogen bonds (dashed lines) between their molecules, so they boil unusually high compared with the extrapolated trend, whereas H₂S, HCl and CH₄ have only van der Waals forces.
Lesson: Hydrogen bonding and van der Waals forces
What it shows
Boiling points of the hydrides of Groups 14 to 17 are plotted against period. Within each group, van der Waals forces grow with molecular size and mass, so boiling points rise from period 3 to period 5. H₂O, HF and NH₃ break this trend and boil far higher than predicted, because an H atom bonded to a small, highly electronegative O, F or N atom is attracted to a lone pair on a neighboring molecule: a hydrogen bond. CH₄ provides the baseline, since Group 14 hydrides form no hydrogen bonds.
How to use
Start with one group under Series shown, then turn on Show extrapolated line (without hydrogen bonding) to see the boiling point expected from the heavier hydrides. Tap a point on the graph, or choose a Molecule in the model, to see the molecules moving with hydrogen bonds drawn as dashed lines, or with van der Waals forces only. Compare H₂O with H₂S, and switch the Temperature unit between °C and K if needed.
Parameters you can change
- Series shown All four series, Group 16: H₂O, H₂S, H₂Se, H₂Te, Group 17: HF, HCl, HBr, HI, Group 15: NH₃, PH₃, AsH₃, SbH₃, Group 14: CH₄, SiH₄, GeH₄, SnH₄
- Molecule in the model H₂O, H₂S, HF, HCl, NH₃, PH₃, CH₄
- Show extrapolated line (without hydrogen bonding)
- Temperature unit °C, K
Questions to explore
- Why does the boiling point rise from H₂S to H₂Te, while H₂O boils highest of all?
- Does CH₄ follow the trend of the other Group 14 hydrides, and which intermolecular forces explain this?
- How many hydrogen bonds can one H₂O molecule form, and why does water boil higher than HF?
