Many pure metals are too soft for many uses. They can be made harder by adding another element to the pure metal, so forming an alloy. This explains why an alloy often has more uses than the pure elements it is made from.
Pure iron, for example, is very soft. Adding a small amount of tungsten to iron makes tool steel, which is harder than pure iron. Steels are examples of alloys. There are many types of steel.
|Mild steel||Carbon and iron||Easy to bend and pull into wires|
|Tool steel||Tungsten and iron||Hard, can be heated to high temperatures|
|Stainless steel||Chromium and iron||Hard, does not rust easily|
In the solid state, a pure metal has a giant metallic structure. The atoms are arranged in layers. When a force is applied, the layers may slide over each other. The greater the force needed, the harder and stronger the metal.
In a pure metal, the force needed to make the layers slide over each other is small. This explains why many pure metals are soft.
In an alloy, there are atoms of different sizes. The smaller or bigger atoms distort the layers of atoms in the pure metal. This means that a greater force is required for the layers to slide over each other. The alloy is harder and stronger than the pure metal.
Explain why steel, which is an alloy of iron, is harder than pure iron.
Steel contains atoms of other elements as well as iron. These atoms have different sizes to iron atoms, so they distort the layers of atoms in the pure iron. This means that a greater force is required for the layers to slide over each other in steel, so steel is harder than pure iron.