The Reactivity Series

The reactivity series is a list of metals (plus carbon and hydrogen) arranged by how easily they react. More reactive metals lose electrons more easily to form positive ions. In simple form: $\mathrm{M} \to \mathrm{M}^{n+} + ne^-$.

Order to Learn

Most reactive → least reactive: potassium, sodium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper, silver, gold.

Why this order?

• Metals high in the series form positive ions easily (they lose electrons quickly).
• Metals low in the series resist losing electrons, so they react slowly or not at all.

Reactions with Water and Steam

• Potassium, sodium, calcium react with cold water to make a hydroxide and hydrogen gas. Example: $$2\,Na + 2\,H_2O \to 2\,NaOH + H_2$$
• Magnesium reacts very slowly with cold water but reacts with steam: $$Mg + H_2O(g) \to MgO + H_2$$
• Zinc, iron, copper, silver, gold do not react with cold water.

Reactions with Dilute Acids (e.g., HCl)

• Metals above hydrogen in the series react with acids to make a salt and hydrogen gas.
• Examples: $$Mg + 2\,HCl \to MgCl_2 + H_2$$ $$Zn + 2\,HCl \to ZnCl_2 + H_2$$
• Copper, silver, gold do not react with dilute acids.

Displacement Reactions

A more reactive metal will displace a less reactive metal from its solution.

• Example: zinc placed in copper(II) sulfate solution forms copper: $$Zn + Cu^{2+} \to Zn^{2+} + Cu$$ Zinc is oxidised (loses electrons); copper ions are reduced (gain electrons).

Aluminium’s Oxide Layer

Aluminium is quite reactive, but it seems unreactive because it is coated by a thin, tough aluminium oxide layer. This layer acts like a protective jacket and stops water and acid reaching the metal.

Deducing Order from Experiments

• Compare fizzing (hydrogen made), temperature rise, and speed in acid or water.
• See which metal displaces another from a solution.