Ranking the metals
Metals differ greatly in how eagerly they react. Potassium fizzes violently in water, iron rusts slowly, and gold barely reacts at all. Arranging metals in order from the most reactive to the least reactive gives the reactivity series, one of the most useful tools in chemistry.
Key idea
A common order (most → least reactive): potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, copper, silver, gold. A more reactive metal can displace a less reactive metal from its compound.
How we judge reactivity
We compare how vigorously metals react with water, with dilute acid, and with oxygen. A reactive metal such as calcium reacts quickly with cold water and with acid, giving off hydrogen gas. A less reactive metal such as copper does not react with water or dilute acid at all. The more vigorous the reaction, the higher the metal sits in the series.
Example
When an iron nail is placed in blue copper(II) sulphate solution, the iron (more reactive) displaces the copper. The nail becomes coated with reddish-brown copper and the blue colour fades: iron + copper(II) sulphate → iron(II) sulphate + copper.
Displacement reactions
A displacement reaction is the direct evidence of the series: a metal higher up can push out (displace) a metal lower down from a solution of its salt. This idea explains why some metals are used to protect others and why reactive metals are stored carefully.
Remember
- Higher in the series = more reactive.
- A more reactive metal displaces a less reactive one from its compound.
- Copper, silver and gold are low in the series and react very little.