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Metals are giant lattices of positive ions arranged in regular layers, with delocalised electrons free to move throughout the structure. Their properties include:

• high melting and boiling points. High temperatures are required to break strong metallic bonds.
• good electrical conductivity. Metal’s delocalised electrons can move and carry charge.
• malleable and ductile. Metal’s layers of ions can slide over each other, but are still held together by the delocalised electrons. This means metal is malleable (it can be hammered into shape) and ductile(it can be drawn out into wires).

Alloys

An alloy is a mixture of two or more elements, at least one of which is a metal. The mixture has metallic properties.

Alloys have metallic structures, but the different sized atoms of the different elements distort this structure. This makes it more difficult for the layers to slide over one another. Alloys are therefore harder than pure metals.

Gold

The gold used for jewellery is alloyed with other metals, often silver, copper or zinc. This strengthens the jewellery while maintaining its shine.

The proportion of gold in the alloy is measured in carats. 24 carat gold is pure gold, while 18 carat gold is 75% pure gold.