Materials and their structure PDF

## 2 Materials and their structure ### 2.1 Solids, liquids and gases In this topic you will: - sort the states of matter into solids, liquids and gases - learn about the properties of solids, liquids and gases - use particle theory to describe the structure of solids, liquids and gases - use parti...

## 2 Materials and their structure ### 2.1 Solids, liquids and gases In this topic you will: - sort the states of matter into solids, liquids and gases - learn about the properties of solids, liquids and gases - use particle theory to describe the structure of solids, liquids and gases - use particle theory to learn about the properties of solids, liquids and gases. #### Getting started 1. Name two solids, two liquids and two gases. 2. Copy and complete the table. Use the substances you listed in Question 1. Discuss your reasons for each decision with your group. | Substance | Solid, liquid or gas | I know this because... | |---|---|---| | Example: tap water | liquid | I can pour it. | #### Key words - compressed - flow - hypothesis - matter - particle - pour - property - states of matter - theory - vacuum - vibrate - volume ### Looking at states of matter Everything you can see and feel is called *matter*. Scientists sort matter into three groups or states called 'solids', 'liquids' and 'gases'. These states of matter behave in different ways. The ways they behave are called their properties. #### Solids Solids keep the same shape. Solids take up the same amount of space. Solids keep the same volume. Solids cannot be compressed (squashed) or poured. #### Liquids Liquids take the shape of the container they are in. Liquids can be poured. Liquids cannot be compressed. Liquids take up the same amount of space, whatever shape their container. The volume of a liquid does not change. #### Gases Gases flow like liquids. They will fill any closed container they are in. Gases are very easy to compress. The volume of a gas can change. Gases weigh very little. Generally, you cannot see or feel gases, but you can sometimes smell them, and you can feel air moving on your face. ### Scientists look at what matter does Scientists try to explain what they see. Here are some examples of how matter behaves that scientists have tried to explain. - You can smell food cooking in another room. - Some substances get bigger when you heat them. - Liquids, such as water, change to a gas when you heat them. - Substances change from liquid to solid if you cool them. Scientists think about why these things happen and try to come up with ideas to explain it. They form an *hypothesis*, which is a suggestion for an explanation. This hypothesis can then be tested by carrying out more investigations. When an hypothesis has been tested and widely accepted as valid by other scientists, it is called a theory. The best theory to explain how matter behaves uses the idea of *particles*. Particles are tiny portions of matter. This theory says that all matter is made of tiny particles arranged in different ways. #### Particle theory All matter is made up of tiny particles that are much too small to see. The particles are arranged differently in solids, liquids and gases. #### Solids In solids the particles are arranged in a fixed pattern. The particles are held together strongly and are tightly packed together. This is why solids have a fixed shape. The particles in a solid can *vibrate* (make small movements) but they stay in the same place. #### Liquids In liquids the particles touch each other. The particles are held together weakly. The particles can move past one another but they still touch each other. Liquids can change shape. #### Gases In gases the particles do not touch each other. They are a long way apart. The particles spread out by themselves. The particles can spread out to fill up the space they are in. Gases can change shape. ### Think like a scientist #### Modelling the particles in solids, liquids and gases In this task, you will describe the strengths and weaknesses of a model. - Work in a small group. - Arrange yourselves in a pattern, as if you are the particles in a solid. - Now arrange yourselves as if you are the particles in a liquid. - Now arrange yourselves as if you are the particles in a gas. ##### Questions 1. With a partner, discuss and describe the ways in which the particles are arranged in the three states of matter. 2. Copy and complete these sentences to describe how particles are arranged in solids, liquids and gases: - In solids, the particles are arranged... - In liquids, the particles are arranged... - In gases, the particles are arranged... ##### Self-assessment In what ways was your group a good model for the particle theory? Think about how well you did for each of the solid, liquid and gas models. - Were you in regular rows? - Were you touching the people around you? - Could you change your position? ### Explaining the properties Matter can only *flow* (be poured) if the particles can move past one another. Matter can only change volume if the particles can spread out or move closer together. #### Solids The particles in a solid are very close together. This makes it difficult for the volume of a solid to be made smaller. Solids have a fixed shape because attractive forces hold the particles together. These forces stop the particles from moving around. The particles can only vibrate. This means that a solid cannot flow. #### Liquids The volume of a liquid cannot be changed. The particles are very close together and cannot be squashed. The particles touch each other but they can move past each other. The attractive forces between the particles are weak enough to allow them to move but strong enough to hold them together. #### Gases Particles in a gas are a long way apart so they can move quickly in all directions. The particles can move easily because there are no attractive forces between them. This means that gas has no fixed shape or volume. When you squash a gas, the particles move closer together and the gas takes up less space. #### No particles? A space where there are no particles at all is called a *vacuum*. A vacuum contains nothing. ### Think like a scientist #### Particle theory Scientists observe the world around them and think carefully about what they see. Development of the particle theory was based on the observations that scientists made about how solids, liquids and gases behave. Scientists saw that most solids cannot be compressed. Can you think of any solids that do not fit the rules of particle theory? Think about the properties of a sponge or a marshmallow. Can a sponge be compressed? #### Questions 1. Use particle theory to explain how a sponge can be a solid, but it can also be compressed. 2. How well does particle theory explain the properties of solids, liquids and gases? 3. What are the strengths of the particle theory? 4. What are the weaknesses of the particle theory? ### Activity #### States of matter On a large piece of paper, draw three large squares and label them 'solid', 'liquid' and 'gas', like this. Leave space around them. | Solid | Liquid | Gas | |---|---|---| In each square, draw how the particles are arranged in that state of matter. In the spaces around the squares, write the properties of the three states of matter. #### Summary checklist - I can classify matter as a solid, liquid or gas. - I can list the properties of solids, liquids and gases. - I can describe the way in which particles are arranged in solids, liquids and gases. - I can explain the properties of solids, liquids and gases using particle theory. ### 2.2 Changes of state In this topic you will: - practice measuring the volume and the temperature of a liquid - learn what happens when matter changes state - investigate the temperature increase when you heat water. #### Getting started With a partner, draw three diagrams to show the particle structure of a solid, a liquid and a gas. Be ready to show the class when you are asked to do so. #### Key words - boil - boiling point - change of state - condensation - condense - evaporation - freeze - measuring cylinder - melt - melting point - meniscus - steam - thermometer - water vapour