1. PARTICLE MODEL OF SOLIDS, LIQUIDS AND GASES
In This Section We Will Be Studying The Following Topics:
Expansion.
The States of Matter.
Matter and Particles.
Diffusion.
Dissolving.

2. PARTICLE MODEL OF SOLIDS, LIQUIDS AND GASES
All substances belong to one of three groups:
Solids.
Liquids.
Gases.
These are called the ‘three states of matter’.
Solids, liquids and gases behave differently because the particles they are made from are arranged in different ways.

3. PARTICLE MODEL OF SOLIDS, LIQUIDS AND GASES
These have a fixed shape and a fixed volume.
Their particles are very close together. They are held in place by strong forces (bonds).
Their particles cannot move around but they do vibrate Because they cannot move around, a solid has a fixed shape.

4. PARTICLE MODEL OF SOLIDS, LIQUIDS AND GASES
In a solid, particles vibrate around a fixed point.
Because they are bonded together the particles can’t move around.
This means the solid will keep its shape.

5. PARTICLE MODEL OF SOLIDS, LIQUIDS AND GASES
These do not have a fixed shape but they do have a fixed volume.
Their particles are very close together. Most of the particles touch each other.
Their particles move around as well as vibrate and because the particles can move around, a liquid will take the shape of its container.

6. PARTICLE MODEL OF SOLIDS, LIQUIDS AND GASES
A liquid will take the shape of its container because its particles can move around.
This is why a liquid flows.

7. PARTICLE MODEL OF SOLIDS, LIQUIDS AND GASES
These do not have a fixed shape or a fixed volume.
Their particles are as far apart as space allows. They will spread out to fill the space available. This is why a gas will fill its container.
Their particles move around all the time.

8. PARTICLE MODEL OF SOLIDS, LIQUIDS AND GASES
The same amount of a gas can be squashed into a small container or be allowed to spread out to fill a large container.
A gas causes a pressure because its particles hit the side of the container.
In which of these containers is the gas likely to have a higher pressure?
Why?

9. PARTICLE MODEL OF SOLIDS, LIQUIDS AND GASES
Answer:
The gas in the smaller container will produce more pressure.
This is because the particles hit the sides of the container more often.
The particles do not have as far to travel before they hit a wall.

10. PARTICLE MODEL OF SOLIDS, LIQUIDS AND GASES
So – is it a solid, a liquid or a gas?
Use the flowchart to help you find out what these are.
Milk.
Wood.
Oxygen.
Sand.
Jelly.
Does it have a fixed shape ? No
Yes
It’s a SOLID.
Does it have a fixed volume?
Yes No
It’s a LIQUID.
It’s a GAS.

11. PARTICLE MODEL OF SOLIDS, LIQUIDS AND GASES
Answers:
Milk …….liquid.
Wood……solid.
Oxygen…..gas.
Sand…….solid.
Jelly……..solid.
So why is sand a solid?
Though a pile of sand does not have a fixed
shape, each individual grain of sand does.
This means sand is a solid.
A single grain of sand.
A pile of many sand grains.

12. PARTICLE MODEL OF SOLIDS, LIQUIDS AND GASES
Scientists believe that everything is made up of particles.
This is an example of a scientific theory.
Scientists look for evidence to support their theory.
Sometimes scientists find evidence that suggests that a theory is wrong.
They will then recheck their evidence.
After rechecking they may have to change their theory.
Other evidence that scientists have used to support the theory that everything is made out of particles include:
Diffusion, Gas Pressure, Liquids Mixing, Expansion and Dissolving.

13. PARTICLE MODEL OF SOLIDS, LIQUIDS AND GASES
Diffusion:
This is the movement of particles of one substance through those of another substance.
Both types of particles
will be moving around randomly.
After a while they will
be completely mixed up.
Diffusion is only possible for Liquids and Gases.
Which of the two diffuses the easiest?
Gas particles have the most freedom to move.
Solids do not diffuse, why?
The particles in solids are held together.

14. PARTICLE MODEL OF SOLIDS, LIQUIDS AND GASES
You can also use the idea of diffusion to explain how liquids mix together and why solids dissolve in liquids.
If the solid dissolves, the bonds between the particles break and the particles become mixed up.
Sugar dissolving in tea.
Solid.
Liquid.

15. PARTICLE MODEL OF SOLIDS, LIQUIDS AND GASES
Expansion - We can use the particle theory to explain why solids expand when they are heated.
The hotter a substance is, the more energy its particles have.
When a solid is heated, its particles gain energy.
This makes the particles vibrate further apart and faster.
To do this, they need more room.
This makes the solid bigger.
The PARTICLES DO NOT GET BIGGER !
COLD
WARM
Heat

16. PARTICLE MODEL OF SOLIDS, LIQUIDS AND GASES
Liquids and gases also expand when they are heated.
This is because their particles also gain energy so they move faster and move further apart.
Why does the pressure of a gas increase when the gas gets hotter?
Answer:
Because the gas particles have more energy and they move faster.
This makes them hit the sides of the container harder and more often.
This makes the gas pressure bigger.

17. CHECK YOUR LEARNING What are the three states of matter?
Solids have a fixed__________?
Liquids have a fixed_________?
When gas particles hit the sides of their container they cause ________?
What is diffusion?
Why does sugar dissolve in tea?
If a solid is heated what happens to it?

18. CHECK YOUR LEARNING - ANSWERS
Solid, Liquid & Gas.
Solids have a fixed Shape.
Liquids have a fixed Volume.
When gas particles hit the sides of their container they cause Pressure.
It is the movement of particles of one substance through those of another substance.
The liquid breaks the bonds between the solid particles and so the solid and liquid particles become mixed up.
It expands.