Only 1.75 hours is allocated to this section in CAPS which is quite short. If you do not have time to do all the activities, then leave out the third activity on the states of water.
We have learnt that matter can exist in 3 different states: solids, liquids and gases. All the materials around us are in one or more of these three states. For example, you have all three states in your body! There is bone in your skeleton. There is water in your blood. There is air in your lungs. We have also learnt that each of the states (solids, liquids and gases) has unique properties:
We know when we have a solid or a liquid. It is easy to see a solid or a liquid. We cannot normally see gases. We can still check that gases are present by seeing their effects.
Why do solids keep their shape but liquids and gases flow? Why does a liquid stay inside an open container (unless it is poured out), but a gas escapes?
We have to look deep inside each state for the answers to these questions. We will have to use our imaginations like never before!
Did you know that all matter is actually made up of very small particles? These particles are called atoms and molecules, and we will learn more about them much later. For now, we are going to use the term particle to describe the smallest 'building blocks' that matter is made of.
The particles that matter is made of are very, very small. Much, much smaller than a tiny grain of sand. Much, much smaller even than a speck of dust! Do you have any idea how small that is?
It is hard to imagine, isn't it Tom? Most people find it very hard to think about, so do not worry, we will go through it slowly.
The particles that matter is made of are much too small to see with the naked eye. They are even too small to see with a strong microscope. So how do we know they exist? Scientists, with special microscopes and other special scientific instruments, have collected evidence that they exist. It is now a well-known and accepted fact that all matter is made up of particles.
Let's imagine that we can shrink ourselves down to the size of such a 'matter particle'. What would we see if we could look around inside a solid?
We would see the particles in the solid are packed tightly together. This explains why solids cannot be squeezed into a smaller shape - solids cannot be compressed .
We would also see that the particles in the solid have fixed positions; they cannot move from their positions. This explains why solids keep their shape.
If we could shrink ourselves down to the size of a 'matter particle', and we could look around inside a liquid, what would we see?
We would see that the particles in the liquid are also very close together. Like solids, liquids cannot be compressed either.
Unlike solids, the particles in a liquid do not have fixed positions. They are always moving around. This explains why liquids flow, to take the shape of their container.
If we could shrink ourselves down to the size of a 'matter particle', and we could look around inside a gas, what would we see?
We would see that the particles in the gas are far apart. The spaces between the particles are huge compared to the size of the particles themselves. These spaces are empty! We call this a vacuum. This explains why gases can be compressed - they can be squeezed into a smaller shape by pushing them closer together. We can make the spaces between them smaller.
The "space" between the particles is empty. It is a vacuum. It is not filled with "air" which is actually a mixture of other gases. If learners ask "There can't just be nothing?", that is just the answer - there is nothing. There is empty space between the particles, just as in outer Space, there is a vacuum. A vacuum is a space entirely devoid of matter. Note that the space between atoms, regardless of the state of matter, or even inside atoms, is vacuum as well. Even the spaces between particles (atoms) in a solid is a vacuum, but these spaces are just much, much smaller compared to the spaces in a gas.
The particles of a gas are always moving freely. If they are in a closed container, they will spread out to fill the whole container. If they are in an open container they will not stay inside for long. They will flow out of the container, and disperse (disperse means to spread out over an area or space.)
This activity would be best performed in a big space, possibly outside on a field. Divide the class into groups. Each group should have enough learners to be able to do the activity meaningfully (ie. 3 is too little in a group, but 8-10 would be ideal). Each group will pretend to be all 3 states so that they get an idea of the difference. There are two key issues here: the submicroscopic behavior of individual particles and the bulk or aggregate effect.
This activity should also be used to revise the role that adding and removing of energy play in changing states. Change of state was dealt with in Gr. 4 and Gr. 5, but not in Gr. 6, so this activity does present an opportunity to revise the concept. An idea is to go through each of the states first so that they can all have a chance being a particle in a different state and you can correct their movements/behaviour. And once they have done this, you can then do the activity again and they can then do the transitions between the states. This emphasises that it is the same particles in each state, just their behaviour changes as energy is removed or added.
NB. Another aspect to be aware of when doing this activity, is that this activity may introduce the idea that the particles make decisions. This need not be addressed with the learners, but it is important to be aware of the possible misconceptions which could be introduced with any metaphors used in science education.
In this activity we are going to pretend to be particles! We are going to behave in the same way that particles do in the 3 different states of matter.
Your teacher will divide the class into groups and then we will go through the different states pretending to be the particles!
INSTRUCTIONS:
Solid:
Since you are the particles in a solid, you should sit or stand as closely as possible to (touching) each other, in neat rows, and move your body, but without moving your feet.
The particles must bump around independently, not sway in unison (as happens once or twice in the video).
If we wanted to move these particles from their fixed positions, what should we give them?
The particles should be given energy.
If we wanted these particles to move into fixed positions again and not move around, what must we take away from them?
We should take away some of their energy.
When you get learners to change state from a solid to a liquid, it is VERY important to stress the point that the particles remain the same on the solid, liquid or gas state - it is just their behaviour which changes. A common misconception is that solids have particles that are solid; liquids, particles that are liquid, and gases have particles that are gases. This is not true as the particles are the same in each state. By getting learners to act out each state they will see that it is the same group of people in each state - just their behaviour and movement changes.
Liquid:
If we wanted to move these particles further away from each other, what should we give them?
The particles should be given energy.
If we wanted these particles to move into fixed positions and not move around, what must we take away from them?
We should take away some of their energy.
Teacher note: For the gas state, you could provide each group with a "container" that they have to remain within, such as placing a piece of string out on the ground in a square.
Gas:
If we wanted these particles to move more slowly and come closer to each other, what should we take away from them?
We should take away some of their energy.
If we wanted these particles to move into fixed positions and not move around, what must we take away from them?
We should take away even more of their energy.
How do we decide whether a material is a solid, a liquid or a gas? The next activity will help us answer that question. We are going to think about some everyday materials. We will use our skills of observation to decide whether they are liquids, solids or gases.
Can you remember what your skills of observation are?
Skills of observation are the skills that involve our senses. In today's activity we will be looking at materials and thinking about how their particles might be behaving.
Once we have decided whether a material is a solid, a liquid or a gas, we can make some predictions about the behaviour of the particles in each material. For this we will need our imagination, as particles are much too small to see with the naked eye.
In the video on "Solids, liquids and gases", forces are mentioned (attraction and repulsion), but have not been dealt with yet at this stage. Be aware too that the animation of the two molecules in the solid chocolate as it melts better reflects the situation in a transition to the gaseous state (they bump around in a rectangular box). But this video still provides some sort of animation of a difficult concept.
Here you should try to make the link between the observable (macroscopic) and imagined (submicroscopic) worlds that is so important in conceptual development for science. What we see (what we observe on a macroscopic level) tells us more about what is occurring on a submicroscopic level. For instance, the fact that a solid keeps its shape tells us that the molecules in the solid stay in their respective places. Conversely, a submicroscopic understanding helps us to explain what we observe on a macroscopic level. For instance, the knowledge that there are large empty spaces between the particles of a gas helps to explain why two gases mix so easily (a process called diffusion). Remember that this empty space is just that - there is a vacuum between the particles. Also, diffusion occurs relatively easily in miscible liquids. It's not just spaces but also particle speed and freedom to change position that play roles here.
INSTRUCTIONS:
The table below contains a list of containers:
1. Say what material is usually kept in each container. Write your answers in the middle column.
2. Say whether the material is a solid, a liquid or a gas. Write your answers in the column on the right.
|
Container |
What material is inside? |
Is this material a solid, liquid or gas? |
 |
Air (actually helium gas as they are floating) |
Gas |
 |
Water, and if boiling then steam (which escapes from the container) |
Liquid inside the kettle, steam is a gas |
 |
Ice |
Solid |
 |
Air |
Gas |
 |
Milk |
Liquid |
 |
Oil |
Liquid |
NB. In the above example of a kettle it is very important to take note of what steam is. Steam IS NOT the suspension of very fine water droplets which you are able to see coming out of the kettle. This is actually water in the liquid state, but the droplets are so fine that they are suspended in the air. This misconception arises as in common language, it is often used to refer to the visible mist of water droplets formed as water vapour condenses in the presence of cooler air. People talk about the steam coming out of the kettle or off a mug of coffee which you can see. This is incorrect in terms of physics and chemistry as true steam is invisible. Steam is rather the transparent mixture of gaseous water and air, which is not visible. Steam is the technical term for water vapour, the gaseous phase of water, which is formed when water boils. Water vapour cannot be seen.
In the table below there are 3 pictures.
1. Look at how the particles are arranged in each picture and say whether it represents a solid, a liquid or a gas. Write your answer in the middle column.
2. For each picture, choose 2 examples from the previous table and write them in the column on the right.
|
Pictures of particles |
Solid, liquid or gas? |
Examples of materials |
 |
Gas |
Air, steam |
 |
Solid |
Ice, ice cream |
 |
Liquid |
Water, milk, oil |
Draw a picture of the particles inside each of the following examples:
1. bar of soap
2. cup of tea
3. balloon
In the previous activities we learnt about the behaviour of the particles inside materials. In the next activity we will learn about the particles in different states of the same material.
In the first activity, the learners in your class acted out the behaviour of particles in a solid, liquid and gas. When the 'liquid' learners changed to 'solid' learners, did the learners themselves change as they changed from solid to liquid?
(Did John, Sarah and Thandi change into different people?) No, they did not change.
Did they behave differently?
Yes.
In what ways did their behaviour change?
They slowed down. They moved into fixed positions and stayed in those positions.
We know that materials can change from one state to another and back again. Can you think of an example of this?
Ice melting and then freezing again.
What happens to the particles inside a material when it changes from one state to another? The next activity will help us to answer that question.
The objective of this extension activity is to establish that a change in state does not change the characteristics of the particles of a material, they only change the behaviour of the particles. If you cannot watch the video, then use the images supplied below. Although "State Changes" is not specified for Gr. 6 in CAPS, if you have time, it could be a good idea to do this again and refresh what learners did in Gr. 4 as they might not remember and these are important concepts for Physical Science in the higher grades.
INSTRUCTIONS:
QUESTIONS:
What do we call the solid state of water?
Ice
What do we call the liquid state of water?
Water
What do we call the gas state of water?
Water vapour or steam
What do we call the process of ice changing to liquid water?
Melting
What do we call the process of liquid water changing to ice?
Freezing
What do we call the process of liquid water changing to water vapour (steam)?
Evaporation
What do we call the process when steam (water vapour) changes to water?
Condensation
Do the particles in the ice change when the ice melts?
No, the particles stay the same. They are still water particles.
If ice and liquid water have the same particles, why do ice and liquid water have different properties? (Ice is solid and water is liquid.)
The particles of water behave differently in ice and in water. In ice the particles are packed and stay in position. In liquid water the particles are still very close together but they can move around.
How can the water particles in ice be made to move freely? (Think of the 'solid' learners. What did we give them to make them move?)
We should give the particles some energy.
How can we change water to steam?
We must heat the water (give it more energy).
How can we change water to ice?
We must make it cold (take away some of its energy).
How are the particles arranged in a solid?
The particles in a solid are tightly packed into fixed positions.
How do the particles in a gas behave?
The particles in a gas are moving around all the time, and they are far apart. They fill all the space available to them.
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