1. Structure and bonding
page 4

Iron is rarely used as the pure element because it is too soft.

Instead, it is converted into steel, by adding carbon and other elements (usually other metals). A solid produced by cooling a molten mixture of iron and another element is an example of an alloy.

What is an alloy?
Interactive graphic of alloy atom
Picture 1.6 In an alloy, the lattice is disrupted by the alloying elements.
Metals can readily form alloys with iron because their atoms are a similar size. The atoms of other metals simply replace atoms of iron in the metal lattice. Each metal atom contributes outer electrons to the cloud of delocalised electrons and becomes a positive ion. Attractions are formed between positive ions and electrons in exactly the same way as happens with the pure metal.

However, the presence of a relatively few other ions can significantly change the properties of the material. Steel, for example, is much harder and stronger than pure iron.

[See page 11 for more about alloys.]

Question 1-3.
a) What feature of the atoms of different metals means that they can readily form alloys?

b) Give some examples of other well known alloys.

Summary                   Close
  • iron is rarely used on its own as it is too soft
  • steel is made by adding carbon to iron
  • steel alloys have other metals added whilst molten; these bond into the lattice