To conclude this section on metals, one final point.
So far, consideration has only been given to cases where all the atoms are the same, and a metallic element is the result. However, such metallic substances can be formed from two or more elements, and they are then called alloys.
One of the earliest examples is bronze, an alloy of copper and tin.
Copper and tin are fairly soft metals, but from about 3000 BC a harder metal was produced by heating mixed ores of copper and tin with charcoal, to form bronze. At the atomic level, copper atoms are mixed with tin atoms, a situation which increases the hardness of the material, and consequently bronze was widely used as blades in daggers, the tips of spears or the heads of axes, where copper or tin alone would have been too soft to use.