What an alloy is

1. An alloy is made by melting a metal, mixing one or more other elements into it, and then letting the mixture cool and solidify.
2. The added elements can be other metals, such as the zinc in brass, or non-metals, such as the carbon in steel.
3. An alloy is a mixture, not a compound, because the elements in it are not chemically combined in a fixed ratio.
4. Because it is a mixture, the amounts of each element can be changed to give an alloy with exactly the properties that are needed.
5. Many of the "metals" you use every day are really alloys, including the steel in cars and bridges and the gold in most jewellery, which is mixed with copper or silver.

Brass and stainless steel

1. Brass is an alloy of copper and zinc.
   1. Brass is harder than pure copper, it resists corrosion and it has an attractive gold colour.
   2. Brass is used for door handles, the pins of electrical plugs and musical instruments such as trumpets.
2. Stainless steel is an alloy of iron with other elements such as chromium, nickel and carbon.
   1. Stainless steel is much harder than pure iron and it does not rust in ordinary use.
   2. Stainless steel is used for cutlery, kitchen sinks, saucepans and surgical instruments.

Why alloys are more useful

1. Alloys can be harder and stronger than the pure metals they are made from.
2. Many pure metals are too soft for everyday use, because pure iron bends easily and pure gold scratches easily.
3. Turning a metal into an alloy gives a material that keeps its shape under force and resists wear, so alloys are more useful than pure metals for most jobs.
4. Some alloys also gain other useful properties, such as the resistance to rusting of stainless steel.
5. This is why far more alloys than pure metals are used to make everyday objects.

Uses of alloys

1. The use of an alloy is explained by its physical properties, in the same way as the uses of pure metals.
2. Stainless steel is used for cutlery because it is hard, so knives and forks do not bend, dent or scratch easily.
3. Stainless steel is also used for cutlery because it is resistant to rusting, so it stays clean and shiny after being washed many times.
4. Pure iron would make poor cutlery, because it is softer and it rusts in contact with water and air.
5. Brass is used for plug pins because it conducts electricity and is harder than copper, so the pins do not bend when they are pushed into a socket.

Identifying alloys from diagrams

1. Structure diagrams show each atom as a circle, so you can tell a pure metal from an alloy by comparing the circles.
2. A pure metal is drawn as identical circles packed in regular rows, because all of its atoms are the same size.
3. An alloy is drawn as rows of one kind of circle with some circles of a different size scattered among them.
4. The different circles may be larger or smaller than the main metal atoms, and they either replace some of the metal atoms or sit in the gaps between them.
5. A diagram showing separate groups of joined circles, with space between the groups, represents a substance made of molecules, not an alloy.
6. The feature that identifies an alloy is two or more types of atom mixed within one closely packed metal structure.