Lesson overview
The particle model: What makes smoke specks jiggle?
Fill a small glass cell with smoke, light it from the side and look through a microscope: mark where one speck is every 2 seconds and find out why it jiggles. Then cool a model of the air, plot the average kinetic energy of its molecules against temperature and find the lowest temperature there can be.
Suggested sequence
- Lesson 1 · Solids, liquids and gases. Properties and changes of state; how the particles are arranged, spaced and move in each state. Read together and discuss (15–20 min), practise with self-checking (20–25 min).
- Lesson 2 · Brownian motion. Why specks of smoke jiggle at random: fast air molecules, far too small to see, hit them unevenly. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 3 · Temperature and absolute zero. Colder means slower particles with less kinetic energy, down to the lowest possible temperature, −273 °C. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- End of module · final check. 2 new questions, 20–30 min, without hints or notes; pupils check their answers once they have answered them all.
- One to two weeks later · return questions. 2 questions, 15 min, lesson closed.
Learning goals
Part 1: Solids, liquids and gases
- Know the distinguishing properties of solids, liquids and gases (2.1.1.1)
- Know the terms for the changes in state between solids, liquids and gases (2.1.1.2)
- Describe the particle structure of solids, liquids and gases in terms of the arrangement, separation and motion of the particles, and represent these states using simple particle diagrams (2.1.2.1)
- Supplement: know that the forces and distances between particles (atoms, molecules, ions and electrons) and the motion of the particles affect the properties of solids, liquids and gases (2.1.2.6)
Part 2: Brownian motion
- Know that the random motion of microscopic particles in a suspension is evidence for the kinetic particle model of matter (2.1.2.4)
- Describe and explain this motion (Brownian motion) in terms of random collisions between the microscopic particles in a suspension and the particles of the gas or liquid (2.1.2.5)
- Supplement: know that microscopic particles may be moved by collisions with light fast-moving molecules, and use the terms atoms or molecules as distinct from microscopic particles (2.1.2.8)
Part 3: Temperature and absolute zero
- Know that the random motion of microscopic particles in a suspension is evidence for the kinetic particle model of matter (2.1.2.4)
- Describe and explain this motion (Brownian motion) in terms of random collisions between the microscopic particles in a suspension and the particles of the gas or liquid (2.1.2.5)
- Supplement: know that microscopic particles may be moved by collisions with light fast-moving molecules, and use the terms atoms or molecules as distinct from microscopic particles (2.1.2.8)
- Describe the relationship between the motion of particles and temperature, including the lowest possible temperature (−273 °C), absolute zero, where the particles have least kinetic energy (2.1.2.2)
Misconceptions to listen for
- “The water spreads along the bottle, so it now takes up more than 300 cm³.” — Spreading out changes the water’s shape, not its amount. A liquid has a fixed volume: it is still 300 cm³ however the bottle lies.
- “The water keeps its upright shape, so it still takes up exactly 300 cm³.” — The volume is right, but a liquid has no fixed shape. As the bottle tips, the water flows into the lowest part and takes the shape of that part of the bottle.
- “The air is squashed into one bubble, so the water now takes up 700 cm³.” — Nothing squashes the air, and the water cannot grow. The water keeps its 300 cm³, and the air, a gas, still spreads out to fill the other 700 cm³.
- “A gas has a fixed volume, like a liquid, so “Has a fixed volume” goes with all three states.” — A gas spreads out to fill whatever container it is in, so its volume is the volume of the container. Let some air out of a bottle, and the rest still fills the bottle.
- “Only a liquid flows.” — A gas flows too: air flows through a straw, and gas flows along the pipes to a cooker. Liquids and gases both flow; solids do not.
- “A liquid is easily compressed, like a gas.” — Squeeze a sealed bottle filled right to the top with water, and it hardly gives at all. Only a gas is easily compressed.
- “The coffee granules melt in the hot water.” — Melting is a solid turning into a liquid of its own, like butter in a pan. The coffee dissolves: its particles spread out among the water particles, so it is still coffee, mixed with water.
- “The dew evaporated onto the grass.” — Evaporation is liquid to gas. Dew forms the other way round: water vapour in the air touches the cold grass and turns into liquid. That is condensation.
- “The water in the fish tank boils away.” — Boiling happens at the boiling point, 100 °C for water, all through the liquid, with bubbles. The tank is at room temperature: water leaves only from its surface, which is evaporation.
- “The pasta water is evaporating, because it turns into a gas.” — It does turn into a gas, but all through the liquid, with bubbles, at its boiling point: that is boiling. Evaporation happens only from the surface, below the boiling point.
Scope
The distinguishing properties of solids, liquids and gases and the terms for the changes of state (2.1.1.1, 2.1.1.2); the arrangement, separation and motion of particles in each state, with simple particle diagrams (2.1.2.1); the motion of particles and temperature, with absolute zero, −273 °C, where the particles have least kinetic energy (2.1.2.2); the random motion of microscopic particles in a suspension as evidence for the kinetic particle model (2.1.2.4) and its explanation by random collisions (2.1.2.5); how forces and distances between particles and their motion affect the properties of solids, liquids and gases (2.1.2.6); microscopic particles moved by collisions with light, fast-moving molecules, and the terms atoms or molecules as distinct from microscopic particles (2.1.2.8). Gas pressure and the kelvin scale are in the module on gas pressure; melting, boiling and evaporation in their own module.