Why ice has the most hydrogen bonds
- The idea
- Predict
- See it
- Why
- Check
The idea
“Cold weakens hydrogen bonds, so ice and cold water have fewer of them.”
Ice floats, and floating sounds loose, so it's easy to guess that freezing loosens the bonds. Ice floats because its hydrogen bonds hold the molecules apart.
The short version
The mistake: Cold weakens hydrogen bonds, so ice and cold water have fewer of them.
What's actually true: Hydrogen bonds are weak, so the motion of warm molecules breaks them. Cooling lets more form and last. Ice has the most.
- A hydrogen bond is a weak pull between the slightly positive hydrogen of one water molecule and the slightly negative oxygen of another.
- These bonds break and re-form all the time. Warmer, faster molecules pull free more often, so fewer hold at once.
- In ice, each molecule bonds to four neighbors in a fixed lattice. The lattice holds the molecules farther apart than in liquid water, so ice is less dense and floats.
On the exam: Heat breaks hydrogen bonds. Cold lets them hold. Ice has the most.