Why are some metals reactive and others not reactive?
Grace Fisher from Southampton (age 5-14)
Why is gold so unreactive? It can stay in the ground for thousands of years unchanged as can be seen from ancient treasures that have been dug up. How does gold differ from other metals that tarnish with age?
Sarah Kelly from County Durham (age 35-44)
Ultimately this is due to how the electrons are arranged in the atoms of the metals and the ease or otherwise with which they can be removed (oxidation) to form positive ions (cations). This can be judged in general by how readily metals react with acids to liberate hydrogen. The most reactive (eg. potassium, sodium) liberate hydrogen from cold water very vigorously, lithium and calcium with less vigour and magnesium needs steam or hot water. Zinc and iron will liberate hydrogen form acids. Copper, silver and gold, for example, will not and are very unreactive.
Nothing is ever simple – or it would be too boring – and a metal like aluminium should be reactive with acids but isn’t in practice because it forms a layer of oxide on it’s surface which renders it passive. The history of humankind is linked to this reactivity. Gold and silver either occur freely in nature or can be removed from their ores with relative ease and were known as far back as the Neolithic age. Then came copper (later tin) – bronze age and this was followed by the iron age. Aluminium, which is difficult to extract from its ore has only been produced in commercial quantities for about 100 years even though it is the most abundant metal in the earth’s crust.
John Kilcoyne, scientist behind Brainiac LIVE