1aPrinciples of Chemistry
States of matter — Edexcel Modular - OL (Chemistry) Revision Notes & Topical Questions
15 min read 8 parts Lesson 1 of 9 2 quizzes
Lesson summary
States of matter Edexcel O Level Modular Chemistry notes: understand the three states of matter in terms of the arrangement, movement and energy of the particlesIce is less dense than water because hydrogen bonds hold molecules in an open lattice.Graphite conducts (delocalised el…
- "The particles expand when heated." Correct the statement
- Explain, in terms of particles, why a gas exerts pressure on its container
- State two differences between boiling and evaporation
- A drop of perfume spreads across a room. Explain using the word diffusion
- States of matter Edexcel O Level Modular Chemistry: what to do next
- States of matter Edexcel O Level Modular Chemistry: revision checklist
Section 1 of 8Process & sequence
1
Look at how close the particles are drawn.
2
Check whether they are in a regular pattern.
3
Decide whether they can move past one another.
4
Name the state from those three facts.
5
Use the spacing to explain shape, volume and compressing.
- Spacing
- Pattern
- Movement
- State
- Explain
1
Particles in the solid absorb energy as the temperature rises.
2
Thermal energy becomes kinetic energy, so the particles vibrate more.
3
Expands
The solid expands as the particles move further apart.
4
At the melting point the structure breaks down and the solid melts.
5
Liquid particles spread out and move around each other.
6
Surface particles overcome the intermolecular forces and the liquid evaporates.
7
At the boiling point all particles escape and the liquid boils.
Heating a solid until it becomes a gaswrite these steps in this order; each step is a marking point.
1
Particles absorb energy
2
Thermal energy becomes kinetic energy
3
Particles vibrate more and the solid expands
4
Structure breaks down — melting
5
Liquid particles spread out and move around each other
6
Surface particles overcome intermolecular forces — evaporation
7
At the boiling point all particles escape — boiling
Why the ring of ammonium chloride forms where it does
1
Both gases diffuse from the ends of the tube
2
NH₃ has Mr 17, HCl has Mr 36.5
3
Ammonia particles are lighter, so they move faster
4
Ammonia travels a greater distance in the same time
5
The gases meet nearer the HCl end
6
NH₄Cl forms there as a white smoke ring
Section 2 of 8Compare
| Property | Solid | Liquid | Gas | Reason | Example |
|---|---|---|---|---|---|
| Arrangement | Regular lattice | Random, close | Random, far apart | Strength of forces | Ice / water / steam |
| Movement | Vibrate | Slide past | Fast, random | Kinetic energy | — |
| Compressibility | Negligible | Very low | High | Spaces | — |
| Density | High | High | Low | Particle spacing | — |
| Shape/volume | Fixed/fixed | Container/fixed | Container/container | — | — |
| Ideal behaviour | — | — | At low p, high T | Forces negligible | He closest to ideal |
| Feature | Boiling | Evaporation |
|---|---|---|
| Temperature | Specific — at the boiling point | A range, below the boiling point |
| Where it happens | Throughout the liquid; bubbles form below the surface | At the surface only |
| Particles involved | All particles gain enough energy to escape | Only the highest-energy particles escape |
| Made faster by | Stronger heating at the boiling point | Larger surface area, higher temperature |
Section 3 of 8Worked examples
Worked examples
"The particles expand when heated." Correct the statement.
- The material expands; the particles themselves do not get bigger.
- What happens is that the particles move further apart and vibrate or move more vigorously.
Explain, in terms of particles, why a gas exerts pressure on its container.
- Gas particles move randomly and quickly and collide with the walls.
- Each collision exerts a force; the many collisions over the wall area give the pressure.
- Heating increases the kinetic energy, so collisions are more frequent and a flexible container expands.
State two differences between boiling and evaporation.
- Boiling happens throughout the liquid at a specific temperature (the boiling point) with bubbles forming below the surface; evaporation happens only at the surface, over a range of temperatures below the boiling point,
- and only the highest-energy particles escape.
A drop of perfume spreads across a room. Explain using the word diffusion.
- Perfume vapour particles move from where they are concentrated to where they are less concentrated, by their random motion, with no energy input, until they are evenly spread through the air.
Section 4 of 8Keep going
States of matter Edexcel O Level Modular Chemistry: what to do next
These States of matter Edexcel O Level Modular Chemistry notes covered the key ideas, worked examples and exam technique for this topic. Check your States of matter Edexcel O Level Modular Chemistry understanding with the practice questions below, then reread any States of matter Edexcel O Level Modular Chemistry point you were unsure about before moving on.
States of matter Edexcel O Level Modular Chemistry: revision checklist
1
Revise the main States of matter Edexcel O Level Modular Chemistry definitions until you can write them from memory.
2
Practise States of matter Edexcel O Level Modular Chemistry exam questions under timed conditions.
3
Link each States of matter Edexcel O Level Modular Chemistry idea to a diagram or a worked example.
4
List the common States of matter Edexcel O Level Modular Chemistry mistakes and how to avoid them.
5
Explain one States of matter Edexcel O Level Modular Chemistry idea out loud as if teaching a friend.
6
Summarise States of matter Edexcel O Level Modular Chemistry in five key points on a revision card.
2
Next lesson: 1b Elements, compounds and mixtures — Notes
4
Official syllabus: Pearson Edexcel International GCSEs
Section 5 of 8Key terms
Section 6 of 8Syllabus checklist
1
understand the three states of matter in terms of the arrangement, movement and energy of the particles
2
understand the interconversions between the three states of matter in terms of
- - the names of the interconversions - how they are achieved - the changes in arrangement
- movement and energy of the particles
3
understand how the results of experiments involving the dilution of coloured solutions and diffusion of gases can be explained
4
know what is meant by the terms: - solvent - solute - solution - saturated solution.
- 1.5C know what is meant by the term solubility in the units g per 100 g of solvent 1.6C understand how to plot and interpret solubility curves 1.7C practical: investigate the solubility of a solid in water at a specific temperature
Section 7 of 8Command terms
Command terms
Give / State / Name
Recall a fact; one idea per mark.
Define
Give the exact meaning using the specification keywords.
Describe
Give an account of what happens / the pattern in data, quoting values; no reasons needed.
Explain
Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.
Suggest
Use knowledge in a new context; more than one answer may be accepted.
Compare
Similarities and differences; each point must refer to both items.
Calculate
Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.
Discuss
Explore the issue from different angles and link the points.
Evaluate / Assess
Weigh strengths and weaknesses and reach a supported judgement.
Deduce
Draw a conclusion from the information given.
Justify
Support a statement/choice with evidence.
Section 8 of 8Exam technique
Keywords the mark scheme looks for in this lesson
Keywords the mark scheme looks for in this lesson
Kinetic theory · Ideal gas · pV = nRT · Real gas deviation · Lattice · Vapour pressure · Absolute zero · Allotrope
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.
How to get full marks (examiner guidance)
How to get full marks (examiner guidance)
Use specification keywords exactly (e.g. electronegativity, nucleophile, dynamic equilibrium, activation energy).
Link ideas
Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.
Use the information in the question
“discuss/evaluate” answers must use the data provided and match the number of marks.
Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.
Avoid vague words
“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.
Do not extrapolate a graph line beyond the data or to zero unless asked.
Six-mark extended responses are marked on content AND a logical, linked line of reasoning.
Keywords the mark scheme looks for in this lesson
- Regular / random arrangement — Vibrate — Kinetic energy — Intermolecular forces — Melting point — Boiling point — Evaporation — Condensation — Diffusion — Concentration — Random motion — Relative molecular mass (Mr)
- Say the material expands, the particles spread out. Writing "particles expand" loses the mark.
Diffusion answers need three elements
- Movement from higher to lower concentration; caused by random motion; needs no energy input.
- Give at least one of these per mark and finish with "evenly spread".
Gas pressure and heating
- Chain it: more kinetic energy → particles move faster → collide with the walls more frequently → pressure/volume change.
- Skipping the collisions step loses the reasoning mark.
State-change vocabulary
- Use the exact name for each direction: melting, freezing, boiling, evaporation, condensation.
- "Evaporating" is not the answer to "what happens to steam on cooling" — condensation is.
- On a heating curve, state that the flat section means energy is used to change state, so the temperature does not change.
Marked practiceQuizzes for this lesson
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