Noble & base metals

The old bike in the yard is gathering rust, but grandma's gold ring has been shining like new for decades. Both are made of metal, yet they behave completely differently. The reason: metals differ in how eager they are to react. Once you understand this, you know why jewellery is made of gold, why water pipes are made of copper, and why you should never touch sodium.

Base means eager to react

Base metals give up their electrons easily and therefore like to react with oxygen, water, or acids. Iron slowly combines with oxygen and water to form rust. Sodium is far more reactive still: it reacts violently with water even at room temperature, which is why it is stored under oil in the lab. Noble metals like silver and gold, on the other hand, hold on to their electrons tightly. Gold reacts so little that a ring is still shiny after centuries in the ground. Silver slowly darkens in air, but that thin layer can be polished off, while rust eats through iron bit by bit.

The ranking of metals

Chemists arrange metals in a ranking by how eager they are to react, from very base to very noble. One section looks like this: sodium, magnesium, zinc, iron, copper, silver, gold. The further towards the front a metal sits, the more readily it gives up electrons and the faster it reacts. The further back, the calmer it stays. This order helps with predictions: a more base metal can snatch a reaction partner away from a nobler one. Put a shiny iron nail into a blue copper salt solution and it coats itself with a reddish layer of copper, because the more base iron pushes the nobler copper out of the solution.

The right metal for the right job

The ranking explains many everyday decisions. Jewellery should shine for decades, so we use noble gold or silver, though silver needs polishing now and then. Water pipes are in constant contact with water, so they are made of copper, which barely reacts. Iron is cheap and strong but rusts, so it gets a protective layer of paint or zinc. And sodium? It is useless for anything that touches air or water, but as a reaction partner in chemistry it is irreplaceable.