Mixtures, compounds and elements

Introduction

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 matter, or materials . For example, a cupboard (an object ) is made of wood, nails and hinges (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. In the same way, the raincoats that you wear during bad weather, are made of a material that is waterproof. The electrical wires in your home are made of metal because metals are a type of material that is able to conduct electricity. 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. In this chapter, we will be looking at different types of materials and their properties.

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

• Strength Materials can be strong and resist bending (e.g. iron rods, cement) or weak (e.g. fabrics)
• Thermal and electrical conductivity Materials that conduct heat (e.g. metals) are called thermal conductors. Materials that conduct electricity are electrical conductors.
• Brittle, malleable or ductile Brittle materials break easily. Materials that are malleable can be easily formed into different shapes. Ductile materials are able to be formed into long wires.
• Magnetic or non-magnetic Magnetic materials have a magnetic field.
• Density Density is the mass per unit volume. An example of a dense material is concrete.
• Boiling and melting points The boiling and melting points of substance help 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.

Discussion: everyday materials

Mixtures

We see mixtures all the time in our everyday lives. A stew, for example, is a mixture of different foods such as meat and vegetables; sea water is a mixture of water, salt and other substances, and air is a mixture of gases such as carbon dioxide, oxygen and nitrogen.