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Chapter 2: Classification of matter

2.1 Materials (ESAV)

All the objects that we see in the world around us, are made of matter. Matter makes up the air we breathe, the ground we walk on, the food we eat and the animals and plants that live around us. Even our own human bodies are made of matter!

Different objects can be made of different types of materials (the matter from which objects are made). For example, a cupboard (an object) is made of wood, nails, hinges and knobs (the materials). The properties of the materials will affect the properties of the object. In the example of the cupboard, the strength of the wood and metals make the cupboard strong and durable. It is very important to understand the properties of materials, so that we can use them in our homes, in industry and in other applications.

Cupboard

Some of the properties of matter that you should know are:

• Materials can be strong and resist bending (e.g. bricks, rocks) or weak and bend easily (e.g. clothes)

• Materials that conduct heat (e.g. metals) are called thermal conductors. Materials that conduct electricity (e.g. copper wire) are electrical conductors.

• Brittle materials break easily (e.g. plastic). Materials that are malleable can be easily formed into different shapes (e.g. clay, dough). Ductile materials are able to be formed into long wires (e.g. copper).

• Magnetic materials have a magnetic field (e.g. iron).

• Density is the mass per unit volume. Examples of dense materials include concrete and stones.

• The boiling and melting points of substances tells us the temperature at which the substance will boil or melt. This helps us to classify substances as solids, liquids or gases at a specific temperature.

The diagram below shows one way in which matter can be classified (grouped) according to its different properties. As you read further in this chapter, you will see that there are also other ways of classifying materials, for example according to whether or not they are good electrical conductors.

What materials are products made of?

This activity looks at the materials that make up food products. In groups of $$\text{3}$$ or $$\text{4}$$ look at the labels on food items. Make a list of the ingredients. Can you tell from the ingredients what the food is (i.e. spice, oil, sweets, etc.)? Food products are labelled to help you (the consumer) know what you are eating and to help you choose healthier alternatives. Some compounds, such as MSG and tartrazine are being removed from products due to being regarded as unsafe. Are there other ingredients in the products that are unsafe to eat? What preservatives and additives (e.g. tartrazine, MSG, colourants) are there? Are these preservatives and additives good for you? Are there natural (from plants) alternatives? What do different indigenous people groups use to flavor and preserve their food?

Some labels on food items

Classifying materials

Look around you at the various structures. Make a list of all the different materials that you see. Try to work out why a particular material was used. Can you classify all the different materials used according to their properties? Why are these materials chosen over other materials?