IB Chemistry home > Syllabus 2016 > Structure and bonding > Alloys

Syllabus ref: 4.5

It is assumed that students have a knowledge of the importance of metals in society and the need to make and use alloys.


Alloys are very important in society, far more so than pure metals.

An alloy is a mixture of metals, although occasionally may include non-metals. Due to the nature of metallic bonding and the close packed structures they adopt, it is easy to slip other metal atoms into the lattice that modify the properties of a metal to suit different purposes.

For example, copper is a relatively soft metal, which used to be used for coinage. However, it very rapidly lost the prints on the surface of the coins and they became smooth and relatively difficult to use. The solution was to use an alloy of copper and nickel, which is much harder wearing. Nowadays, the majority of coinage is made from an alloy of these two metals.

Undesirable properties of metals may be softness, easy corrosion, poor conductivity etc. These can often be overcome by the addition of a suitable alloying metal.


Iron and steel

The most commonly used metal in society is steel. Steel is made by blowing oxygen through the molten iron manufactured by the Bessemer (blast furnace) process to remove excess carbon by oxidation to carbon dioxide.

Steel is iron with some carbon impurity and usually other metals are added to adopt the properties of the steel to that desired. Manganese may be added to steel used for springs, tungsten for greater hardness, molybdenum for ball bearings, etc. etc..