Metals differ in how reactive they are. The reactivity series lists them from most to least reactive (potassium, sodium, calcium, magnesium … iron … copper, silver, gold).
A more reactive metal can displace a less reactive one from its compound. Reactive metals react quickly with oxygen, water and acids; gold barely reacts at all.
Remember
- More reactive metals displace less reactive ones.
- Gold and silver are very unreactive.