The particle model says that all matter is made of tiny particles that are always moving, and that the arrangement and energy of those particles explain the states of matter. This module turns that idea into explanations you can write: why a smell spreads, why a kettle boils, why a graph goes flat and why a gas presses on its container.
It is an early module in the Chemistry learning guide because later topics, including reaction rates and energy changes, reuse the same reasoning. Check the current Cambridge IGCSE Chemistry 0620 syllabus for your exam year to confirm the exact scope.
What should you already know?
You should know that matter exists as solid, liquid and gas, and be able to read a table and a simple line graph. You should know that temperature is measured in °C. You do not need any chemical formulas yet, though the final lesson uses the formula H₂O.
An orienting example
Take 18 g of ice at 0 °C and heat it steadily until it becomes steam. The numbers are invented for illustration.
Step 1, particles. Every stage contains the same H₂O molecules. The mass stays 18 g throughout, which is 1 mol, since the molar mass of H₂O is 2 × 1 + 16 = 18 g/mol.
Step 2, the graph. The temperature rises, then goes flat while the ice melts, rises again as a liquid, then goes flat while it boils. The flat sections are where energy changes the spacing of particles, not their speed.
Step 3, what differs. In ice the particles vibrate in fixed positions. In liquid water they slide past each other. In steam they are far apart and move quickly, which is why the gas spreads and pushes on walls.
One example already uses four of the five lessons: diffusion, boiling, the heating curve and pressure.
In what order should you study the lessons?
- Explain diffusion using particle motion: start here, because random motion is the base for everything else.
- Distinguish boiling from evaporation: this applies the same idea to a liquid and sharpens two easily confused words.
- Interpret a heating curve: this links energy, temperature and state in one graph.
- Relate pressure to particle collisions: this explains gas behaviour with frequency and force of collisions.
- Separate a substance change from a change in spacing: this stops a change of state being mistaken for a chemical change.
Then take the mixed practice set and record slips in the mistake log and retest queue.
What are the common traps?
- Stating a definition when the question asks you to explain.
- Saying particles stop moving when diffusion ends or when a substance is cold.
- Treating boiling as fast evaporation.
- Reading a flat section as no heating or no change.
- Saying particles expand when heated, instead of moving faster.
- Splitting water into hydrogen and oxygen when it only boils.
How should you use the practice set?
Write each answer in full sentences first, because these are explanation skills. Then open the worked answer and compare your reasoning with it. The final table in the set sends each error to the lesson that fixes it.
The last lesson introduces amounts and balanced equations. The mole and equation-ratio tutor and the equation balance reasoning trainer let you check that work. Next in the course is atoms, elements and isotopes.
If explanations are where you lose the most marks, a teacher in online one-to-one Chemistry tuition can work on your wording step by step. Your school or exam centre remains responsible for your entry and any practical arrangements.