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Science
The Particle Model (Solids, Liquids & Gases)
Year 8 Chemistry
The Particle Model – Solids, Liquids & Gases
Learn how particles are arranged and move in each state of matter, how changes of state happen, and why diffusion makes smells and colours spread.
Particle Arrangement
Changes of State
Melting & Boiling
Diffusion
Core Ideas Class Notes
Use these notes to introduce the topic before attempting the questions. They show the particle story behind every state change.
P The Particle Model of Matter
The particle model says that all matter (everything around us)
is made of tiny particles that are too small to see.
These particles are always moving and have spaces
between them. The way particles are arranged and how they move
explains the properties of different states of matter.
- Particles attract each other with forces.
- When you heat a substance, you give the particles more energy.
- More energy → faster movement → particles can move further apart.
Tiny particles
Constant motion
Energy & forces
S Solids, Liquids & Gases – Overview
Solids have particles packed closely in a
fixed, regular arrangement. They vibrate but cannot
move from place to place, so solids have a fixed shape and volume.
Liquids have particles that are still close together but in an irregular arrangement. They can slide past each other, so liquids flow and take the shape of their container but keep the same volume.
Gases have particles that are far apart and move quickly in all directions. Gases have no fixed shape or volume and can be compressed.
Liquids have particles that are still close together but in an irregular arrangement. They can slide past each other, so liquids flow and take the shape of their container but keep the same volume.
Gases have particles that are far apart and move quickly in all directions. Gases have no fixed shape or volume and can be compressed.
Solids: fixed shape
Liquids: flow
Gases: compressible
Δ Changes of State
When a substance changes from one state to another, we call this a
change of state. The substance is the same chemical,
but the particles move differently:
- Melting: solid → liquid (particles gain energy and break free from fixed positions).
- Freezing: liquid → solid (particles lose energy and lock into place).
- Boiling: liquid → gas throughout the liquid at a fixed temperature (boiling point).
- Evaporation: liquid → gas at the surface, can happen below boiling point.
- Condensation: gas → liquid (particles lose energy and come closer together).
Energy changes
Same substance
D Melting, Boiling, Evaporation & Diffusion
Melting point – the exact temperature where a solid
turns into a liquid.
Boiling point – the temperature where a liquid boils and turns rapidly into gas.
Evaporation is slower than boiling and happens only at the surface when the fastest particles escape. This is why sweating cools your skin.
Diffusion is the spreading out of particles from a region of higher concentration to a region of lower concentration. It is fastest in gases, slower in liquids and extremely slow in solids.
Boiling point – the temperature where a liquid boils and turns rapidly into gas.
Evaporation is slower than boiling and happens only at the surface when the fastest particles escape. This is why sweating cools your skin.
Diffusion is the spreading out of particles from a region of higher concentration to a region of lower concentration. It is fastest in gases, slower in liquids and extremely slow in solids.
- Higher temperature → faster diffusion (particles move faster).
- Lighter particles diffuse faster than heavier ones.
Boiling vs evaporation
Spreading of particles
True / False 5 Questions
Decide if each statement is true or false, then reveal the answer.
Q1
True / False
In a solid, particles are very close together and vibrate around fixed positions.
Show Answer
True.
Q2
True / False
Gases have a fixed volume but no fixed shape.
Show Answer
False. Gases have no fixed shape or volume.
Q3
True / False
Melting and freezing involve the same temperature for a pure substance.
Show Answer
True. They are reverse changes at the same point.
Q4
True / False
Diffusion happens faster in a warm room than in a cold room.
Show Answer
True. Higher temperature → faster moving particles.
Q5
True / False
Evaporation only happens when a liquid reaches its boiling point.
Show Answer
False. Evaporation occurs at any temperature below boiling, from the surface.
Multiple-Choice Questions 5 Questions
Pick the best answer. Discuss with students why the other options are incorrect.
Q6
MCQ
Which state of matter has a fixed volume but no fixed shape?
Show Answer
B) Liquid.
Q7
MCQ
Which change of state is described as gas → liquid?
Show Answer
B) Condensation.
Q8
MCQ
In which state do particles move the fastest on average?
Show Answer
C) Gas.
Q9
MCQ
Which process best explains the smell of perfume spreading across a room?
Show Answer
B) Diffusion.
Q10
MCQ
At the boiling point of a liquid:
Show Answer
C) Bubbles of gas form throughout the liquid.
Fill in the Blanks 5 Questions
Fill in the missing words to complete each sentence about particles and state changes.
Q11
Fill
In a gas, particles are ______ apart and move quickly in all directions.
Show Answer
Far apart.
Q12
Fill
The change from liquid to solid is called ______.
Show Answer
Freezing.
Q13
Fill
The spreading out of particles from a high concentration to a low concentration is called ______.
Show Answer
Diffusion.
Q14
Fill
When a solid is heated, its particles gain ______ energy and vibrate faster.
Show Answer
Thermal (or heat) energy.
Q15
Fill
A liquid boils when it reaches its ______ point.
Show Answer
Boiling point.
Short-Answer Questions 5 Questions
Answer each question in one or two clear sentences.
Q16
Short
Why are solids difficult to compress?
Show Answer
Because the particles in a solid are packed very closely together with almost no space between them, so they cannot be pushed closer.
Q17
Short
Explain why liquids can flow but solids cannot.
Show Answer
In a liquid, particles are close but can slide past each other, allowing the liquid to flow. In a solid, particles are locked in fixed positions and can only vibrate.
Q18
Short
Why does evaporation of sweat cool your skin?
Show Answer
The fastest, highest-energy particles leave the liquid as gas, so the particles left behind have less energy and the skin temperature drops, making you feel cooler.
Q19
Short
Give one everyday example of diffusion in a gas.
Show Answer
Examples: the smell of perfume or room spray spreading through a room; the smell of cooking reaching another room.
Q20
Short
Why is diffusion slower in liquids than in gases?
Show Answer
In liquids, particles are closer together and move more slowly, so it is harder for them to move long distances compared to the fast, widely spaced particles in gases.
Long-Answer / Explanation Questions 5 Questions
Use these for written homework or extended answers. Students should include particle diagrams or sentences about movement and spacing where possible.
Q21
Long
Describe and compare the particle arrangement and movement in a solid and a gas.
Show Answer
In a solid, particles are packed very close together in a
regular pattern. They cannot move from place to place but
vibrate around fixed positions. In a gas,
particles are far apart with large gaps between them. They move
quickly in all directions and collide with each other and
the walls of the container. This is why solids keep their shape, but gases
spread out to fill any space.
Q22
Long
Explain what happens to the particles of a solid as it melts and then boils.
Show Answer
When a solid is heated, its particles gain energy and vibrate
faster. At the melting point, the vibrations become strong
enough to partly overcome the forces holding them in fixed positions, so the
structure breaks and the particles can slide past each other – the solid
becomes a liquid. As heating continues, particles in the
liquid move faster. At the boiling point, they have enough
energy to completely overcome the attractive forces and break away from the
liquid to form a gas, creating bubbles throughout the liquid.
Q23
Long
Describe an experiment you could do to show diffusion in a liquid and explain the results in terms of particles.
Show Answer
Gently place a drop of food colouring into a beaker of
still water and do not stir. Over time, the colour slowly spreads through
the water until the whole beaker is evenly coloured. This happens because
the dye particles move randomly between the water particles. They slowly
spread from the area where they are most concentrated (the
drop) to areas of lower concentration, showing diffusion in
liquids. Heating the water makes this happen faster because the particles
move more quickly.
Q24
Long
Explain two differences between boiling and evaporation using the particle model.
Show Answer
Boiling happens at a fixed temperature called the
boiling point, and bubbles of gas form
throughout the liquid. All the particles have enough energy
to break free at once. Evaporation can occur at
any temperature below the boiling point and happens only at the
surface of the liquid. Only the fastest, most energetic
particles escape into the air. In both cases, particles change from the
liquid state to the gas state, but the conditions and where it happens are
different.
Q25
Long
A student opens a bottle of vinegar in one corner of the lab. After a short time,
everyone can smell it. Use the particle model and the idea of diffusion to explain this observation.
Show Answer
When the bottle is opened, vinegar particles escape into the air as gas.
These particles are moving quickly and randomly, colliding with air
particles. Because of diffusion, they spread out from an area
of high concentration near the bottle to the rest of the
room where the concentration is lower. Over time the vinegar particles mix
evenly with the air, so people all around the lab can detect the smell.
Higher temperature would make this happen even faster because the particles
would move more quickly.