States of matter E verything around you is made of matter. Anything that has mass and takes up space is matter. The air we breathe, the water we drink and the food we eat are all different types of matter. But air, water and food are very different. One important difference between these items is their state. The three main states of matter are solid, liquid and gas. Gases change shape Gases fill the entire container they are in. The helium gas in balloons changes shape depending on the shape of the balloon. The helium fills every part of the balloon. Solids do not usually flow Most solids are too rigid to flow. Substances such as sugar, which are made up of many small solid pieces, can be poured. The volume of gases changes Gases expand to fill the containers they are placed in. Gases do not have a fixed volume. Solids have a constant shape Solids have a fixed shape and change shape only when a force is applied. The force applied to both ends of this bar by the circus strongman causes the bar to bend. Gases flow Like liquids, gases flow from one container to another. The gas from the helium bottle flows to the balloon through a tube. It is often hard to see gases flow because many of them are colourless. Gases can be compressed Gases can be squeezed so they take up less space (compressed). The gas inside the helium bottle is compressed. It expands when it leaves the bottle and fills the balloons. Solids and liquids cannot be compressed. 22 Science Alive for VELS Level 5
Liquids have a fixed volume The liquid from the jug can be poured into several glasses. The total amount of space taken up in the glasses equals the amount that was originally in the jug. Liquids change shape A liquid s shape changes to fit the container it is in. The shape of the lemonade in these glasses depends on the shape of the glass. Liquids at rest have a flat surface. You will need: Investigating solids, liquids and gases a piece of dowel water salt Copy the following table. large plastic syringe plasticine sponge. Property Solid (dowel) Liquid (water) Gas (air) Fixed shape Fixed volume Able to be compressed Insert the dowel into the syringe. Press down on the plunger. 1. Can the dowel be compressed? Draw some water into the syringe. Put your finger over the end of the syringe and press down on the plunger. 2. Can water be compressed? Draw some air into the syringe. Put your finger over the end of the syringe and press down on the plunger. 3. Can air be compressed? Complete the remainder of the table by looking closely at the dowel and water, and by reading the captions on the circus scene. Investigate the properties of plasticine, salt and sponge. 4. Classify each of the three materials as a solid, liquid or gas. 5. Which materials did you have trouble classifying? Why? Liquids flow Liquids can be poured from one container to another. When the container is full, it overflows. Solids have a fixed volume If you move a solid from container to container, the amount of space it takes up (volume) is the same. REMEMBER 1. What properties do we use to classify materials into the three states? 2. Which state/s of matter: (a) can be compressed? (b) can flow? THINK 3. Classify each of the following items as a solid, liquid or gas. Oxygen Talcum powder Glass Vaseline Oil Honey Wood Sand 4. Why is a bicycle frame made of solids? 23 2. Solids, liquids and gases learning 5. Why are bicycle tyres filled with air? OBSERVE 6. Look carefully at the circus scene on the left. (a) List as many solids, liquids and gases as you can find. (b) Find one example of a substance that can change from one state to another. I CAN: name the three states of matter describe the properties of the three states of matter classify materials as solids, liquids or gases.
The particle model A ll matter is made up of tiny particles. If you could shrink down to microscopic size and watch these particles, you would see that the particles behave differently depending on whether the substance they make up is a solid, liquid or gas. To help explain this different behaviour, scientists have developed a model called the particle model of matter. Models help people understand complex ideas, such as how matter behaves. As new clues about matter have been discovered, the models have been improved. The basis of the particle model is that: All matter is made up of small particles. Particles are always moving. Particles are held together by bonds that vary in strength. As particles are heated, they move more quickly. When the particles are cooled, they move more slowly. Particles in a gas The forces between the particles in a gas are very weak. The particles are in constant motion. This means that gases have no fixed shape or volume. There are large spaces between the particles. The spaces allow the gas to be compressed. A gas can flow and diffuse easily since its particles are always moving. Gas particles have much more energy than solid and liquid particles. They move around and collide with other particles and the walls of the container they are in. Particles in a solid Solids cannot be compressed because the particles inside them are held closely together. There is no space between them. Bonds also hold the particles tightly together in a rigid crystal-like structure. This gives solids their fixed shape and constant volume. The particles in solids cannot move freely; they vibrate in a fixed position. This means that solids are unable to flow. Particles in a liquid The particles in a liquid are close together. So, there is no room for compression between the particles in a liquid. The particles are also held tightly by bonds, but not in the same rigid structure as solids. This gives liquids their fixed volume, but allows the particles to roll over each other. This rolling allows liquids to flow. The movement of the particles explains why liquids take the shape of their container. The particles roll over each other until they fill the bottom of the container. 26 Science Alive for VELS Level 5
Diffusion Diffusion is the spreading of one substance through another. The spreading occurs because the particles of each substance become mixed together. The movement of the particles in liquids and gases makes diffusion possible. As the particles in a gas move faster than in liquids, diffusion happens faster in a gas. Particles are not free to move in a solid, so diffusion cannot occur at all. Air deodoriser The spreading starts in an area where there is a concentration of one of the substances. The particles keep mixing through until they are evenly spread through each other. Investigating diffusion You will need: 500 ml beaker water straw potassium permanganate crystals fragrant spray protective mat safety glasses. Using the straw as a Hold guide, put a crystal of straw potassium permanganate in the bottom of a beaker of water. Remove the straw and record your observations. 1. Draw a diagram of the movement of the potassium permanganate through the water. Crystal Water Beaker Release some of the fragrant spray in one corner of the classroom. Move away and observe by smell. 2. How do you think the fragrant spray moved through the air? 3. This experiment shows diffusion in a liquid (water) and diffusion in a gas (air). (a) Which state diffuses faster liquid or gas? (b) Why do you think this is? REMEMBER 1. What is the basis of the particle model? 2. What is diffusion? 3. Give an everyday example of diffusion at work. 4. Copy and complete the table at right. Property Solid Liquid Gas Particle arrangement Force of attraction between particles THINK 5. Why do solids have a fixed shape? 6. Why can gases be compressed? 7. Why do gases fill their containers? 8. When you pour cordial into water, the two liquids slowly mix together even though you don t stir them. Explain how this happens. Movement of particles Ability to diffuse 27 2. Solids, liquids and gases learning I CAN: describe the particle model of matter describe how the particles move in each of the states: solid, liquid and gas explain how diffusion occurs in liquids and gases.
Change of state and the particle model I magine a very cold day. On days like this, you probably sit inside without moving around too much. As the weather gets warmer, you start to move around a little more. On warm, sunny days, you probably have a lot more energy. On these days, you might feel like moving about more. Much like you, the particles inside matter also change the way they move when they are heated or cooled. Changing state A change of state involves the heating or cooling of matter. As a substance is heated, energy is transferred to it. When a substance cools, energy moves away from it to another substance or to the environment. The change in energy causes the particles in the substance to move at different speeds. Solid When a solid is heated, its particles start to move more quickly. The increased movement of its particles makes the solid expand. Melting As more heat is transferred to the solid, its particles vibrate more violently. Eventually the particles move so much that the bonds holding them in their fixed positions break. The particles start to roll over each other. Melting continues until the entire solid becomes a liquid. Liquid As a liquid is heated, its particles move and roll over each other faster and faster. The liquid begins to expand. Gas As in solids and liquids, the particles in gases move faster and faster when they are heated. The increased movement of the particles means that they take up more space and the gas expands. If the gas is heated in a closed container, the increased movement of the particles means that they collide more often with the sides of the container and with each other. Boiling If the liquid continues to be heated, the particles will eventually have enough energy to break the bonds holding them together. The particles can break away from the liquid and begin to move around freely. This process is called boiling. Boiling continues until the entire liquid becomes a gas. 28 Science Alive for VELS Level 5
Foggy mirrors Have you noticed how the mirror in the bathroom fogs up after a hot shower? The fog is actually formed when water vapour that evaporates from the hot water cools down. Invisible gas Water vapour forms when particles in the hot water gain enough energy to escape and become a gas. You can t see water vapour. The particles in the water vapour move around freely. They have more energy than the particles in the liquid water. Fog in the air Some of the energy of the particles in the water vapour is transferred away from the vapour to the air. The transfer of energy leaves the water vapour with less energy so much less energy that its particles slow down. The transfer of energy away from the water vapour means it cools down and turns into tiny droplets of water. These tiny droplets form clouds. This process is called condensation. Fog on the mirror The energy from some of the water vapour is transferred to the cold mirror. This results in the water vapour condensing on the mirror. REMEMBER 1. What happens to the movement of particles as a substance changes from a solid to a liquid? 2. What happens to the movement of particles as a substance changes from a gas to a liquid? 3. Why do substances often expand when they are heated? THINK 4. The steel rails used in train tracks are placed end to end in a line to form each side of a train track. Gaps are left between the steel rails. Why do you think these gaps are left between the rails? Use the word expansion in your explanation. 29 2. Solids, liquids and gases 5. What is the relationship between the amount of energy the particles in a substance have and the state (phase) of the substance? 6. Explain why many substances contract when they are cooled. TEAMWORK 7. As a class, make a list of structures and substances around your home that undergo expansion and contraction. Divide your list into things that expand and things that contract. learning I CAN: describe what happens to the particles in a substance as it changes state explain why substances expand when heated. Checkpoint