1. The Particle ModelWhat makes up all the matter around us? If we were able to breakup a piece of steel into smaller and smaller parts, what would we getat the end? Would we get the same thing if we broke up a piece ofplastic? Could we break up a droplet of water? Ice, water and steamare all the same chemical substance, yet they behave very differently.How can we explain this?

2. Models are used by scientists because they help to explain manyobservations. Scientists have developed a way of thinking aboutmatter that explains its nature and behaviour. They believe that allmatter is made up of tiny particles, called atoms. These are so smallthat they can only be seen with powerful microscopes. If you couldsee deep inside solids, liquids and gases, how do you think theparticles that make them up might be arranged?

3. The theory that we have to explain the properties of solids,liquids and gases is called the particle model of matter.Solids, like ice, have constant shape because particles of solid arepacked closely together. They cannot move around much, but mainlyvibrate around one point. These particles in solids are held togetherby strong forces.

4. In liquids, such as water, particles are spaced further apart. Theyare held together by weaker forces. This means that they are able tomove around more, and slide over each other. This explains why aliquid will take up the shape of part of the container it is in and canbe poured from one container into another. The ease with which aliquid can be poured is called its viscosity. Honey is more viscousthan water because its particles have stronger forces between them.

5. In gases, like steam, there are large spaces between the particles,and the particles are able to move freely at high speeds and in alldirections. The particles collide with each other and the walls oftheir container. This explains why a gas spreads apart so the gasfills its container. Can you think of some examples of this? Sincegas particles are spread far apart, one type of gas can flow throughanother. In a process known as diffusion, the particles that make upan odour can flow through the particles that make up the air. Thisis how smells spread easily.

6. The particle model of matter tells us that everything is made upof tiny particles called atoms, which are constantly moving. Thebehaviour of these particles is summarised in figure 2.9.

7. States of matter….summaryThere are many ways to think about solids, liquids and gases. Particles in a solid couldbe represented by a group of people packed onto a dance floor, listening to a band,all moving but unable to break through the crowd. A liquid could be represented by abreak in the music and people moving around to get a drink or freshen up. At the endof the night, people move at higher speed through all exits, to public transport andcars, spreading in all directions to go home. Here, they have behaved like a gas.Activity…Working in a group, make up a similar description of your own to explain states ofmatter.Act this out for your class and then see if they can explain your actions.Ask your classmates if they can suggest any ways of improving your model.Make the changes that your group agrees with and then re-enact your role play.