Metals are malleable and ductile; this means they can be made into different shapes; for example, into jewels and car components. They are also good conductors of electricity (copper wires) and thermal energy (heat), so they are used to make cooking pots and saucepans. The high density of metals makes them good materials to make solid structures, like bridges. Some metals - like gold and platinum - are resistant to reaction with oxygen and acids, which makes them very valuable. Bells are usually made of brass, because it is sonorous (makes a rich, full sound). Brass is also used for taps and door handles.
At very low temperatures, some metals become superconductors, i.e. they conduct electricity with no resistance. A permanent magnet would levitate above a superconductor.
Alloys are mixtures of metals and other elements that are more useful. Steel is an alloy of iron and it is much stronger than iron. Bronze is a much harder alloy of copper and tin. It contracts very little when solidifying, so it is easy to make a cast. Amalgam is an alloy used to fill teeth cavities.
There is a wealth of materials used in the manufacture of cars:
- glass for windscreens, because it is transparent
- aluminium in car bodies and wheel hubs, because it is strong, but has a low density and does not corrode
- lead in lead-acid batteries, because it conducts electricity
- PVC in metal wire coverings, because it is flexible, does not react with water and it insulates electricity
- fibre in seats, because it is hard-wearing
Many materials are also used in construction of buildings. Apart from metals and glass, buildings are made from bricks (for small buildings) and reinforced concrete, which contains a steel frame with the walls built inside it from brick, aluminium, concrete or glass.
Calcium carbonate is a compound that decomposes (breaks down) at high temperatures:
Limestone (a form of calcium carbonate) is heated and clay is added to make cement. Cement, sand and gravel are mixed together to make concrete. Cement mixed with sand and water is called mortar, which is used to stick bricks together when building.