In the last lesson we learnt that heating a substance could cause it to change state . Different materials change state at different temperatures. Even if this does not happen, it will expand. What will happen if you cool a substance? It never gains or loses mass.
One question you may have thought about is this. How can a piece of metal get longer, even a bit wider and yet still have the same mass? To answer this question we have to start thinking about materials in a different way. Scientists believe that all things are made of tiny particles. These can be arranged in different ways. Below are three ways that particles can be arranged.
Activity 1
Draw the three diagrams and think carefully what you know about SOLIDS, LIQUIDS and GASES.
Which diagram do you think shows how the particles are arranged in each the states of matter?
Label your diagram and give reasons for your choice. (Think about density, compressibility, flowing, keeping shape)
Completing this table will help with your ideas.
solid liquid gas density compressibilty flow shape Click here if you are not sure of any of the left hand ideas.
Click on the diagram for the answer.
If you have time - try the 'Solid, Liquid and Gas' Game
Activity 2 - Squeezing
Try this experiment. Squeeze with your hands, three large plastic bottles.
Three different fillings Air Water Sand Use the particle diagram to help you make a prediction.
Hardest Easiest Which is easiest to squeeze?
The plunger of a bicycle pump filled with air and the end sealed with a finger can still be pushed in quite a way before the pressure forces air out.
If the pump is then filled with water and the activity repeated, the plunger can hardly move. Why?
Thinking.
If a solid substance is heated until it melts the arrangement of the particles will change.
What difference will melting make to the number of particles in the material?
If the particle move a bit farther apart, what difference will it make to the space or volume the substance takes up?
What's that smell?
If you can smell something pleasant or not so nice then particles are getting up your nose.
Where are they coming from?
From the cooking food, the bunch of roses or something on the bottom of your shoe.
Gas particles certainly can move!
Can the particles in liquid move?
Yes, but not as quickly and as easily as those in a gas. Remember they are still close to each other.
Can the particles in a solid move?
Not very much but they can vibrate. They vibrate even more as they get hot.
Click here for a summary
Diffision is when particles travel from one place to another without any help from us.
Gases diffuse. The smell is diffusing around the room.
Activity 3
Draw a picture to show how a particle of perfume travels from a flower on one side of a room to your nose on the other.
Remember for a small particle it is still along way even if it is moving rapidly. There are lots of obstacles in the way including air particles.
Explain why it is dangerous to light a match or use a mobile phone anywhere near a petrol station.
What I have learnt this lesson.
In this lesson you have seen that when any material is heated the particles from which it is made move apart. When the material cools down then the particles move closer again. This will cause the volume of the material to change. It will increase when heated and decrease when cooled.
Since the total number of particles in the material is the same at all temperatures, the mass always stays the same.
The particles are arranged in different ways in solids, liquids and gases. If a substance changes state during heating then the arrangement of the particles will change.
As the material increases in temperature, the energy of the particles increases. This will make them move around more quickly.
Particles that can move freely diffuse.
