Forces Between Molecules · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

What boiling really breaks

Science · Matter & Materials · ages 15-16
Name ______________________   Date ____________

  1. Which pull between molecules is strongest?

    • Dispersion forces
    • Dipole-dipole attractions
    • Hydrogen bonding

  2. When a pot of water boils, what actually comes apart?

    • The H-O bonds inside each molecule
    • The pulls between whole molecules
    • Oxygen atoms splitting in two

  3. Hydrogen bonding needs hydrogen joined to which atoms?

    • Nitrogen, oxygen, or fluorine
    • Carbon, hydrogen, or helium
    • Sodium, chlorine, or iron

  4. By size alone water should boil far below 0, yet it boils at 100. Why?

    • Its inner H-O bonds are weak
    • Hydrogen bonds grip its molecules tightly
    • Tiny molecules always boil high

  5. Candle wax melts far above tiny methane. Why?

    • Wax molecules are bigger, so dispersion grips harder
    • Wax forms hydrogen bonds
    • Methane has weaker bonds inside

  6. To rank boiling points, check hydrogen bonding first, then polarity, then size.

    Circle one:   True   False

  7. A brimful glass holds a dome of water above the rim. What holds the dome up?

    • The glass pushing the water upward
    • Inner bonds stretching like rubber
    • Cohesion through hydrogen bonds

  8. Fluorine and chlorine are gases, bromine is liquid, iodine is solid. Why?

    • Only the solids form hydrogen bonds
    • Dispersion forces grow as the molecules get bigger
    • The inner bonds weaken down the group
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Answer key

For grown-ups. Fold this page away before handing over the rest.

What boiling really breaks W1-mt_0uBZWotvZB-s1

  1. Hydrogen bonding · Hydrogen bonding tops the three strengths you met.
  2. The pulls between whole molecules · Boiling separates molecules while each H2O stays whole.
  3. Nitrogen, oxygen, or fluorine · Only N, O, or F set up this strong link.
  4. Hydrogen bonds grip its molecules tightly · The hydrogen bond grip needs much heat to break apart.
  5. Wax molecules are bigger, so dispersion grips harder · Bigger molecules carry stronger dispersion forces.
  6. True · That order follows the strengths from strongest to weakest.
  7. Cohesion through hydrogen bonds · Water molecules grip each other, which is cohesion.
  8. Dispersion forces grow as the molecules get bigger · Size grows down the group, and dispersion grows with it.
Worksheet · LightMySky