Cambridge O Level Chemistry · Syllabus 5070 · Metals
Reactivity Series
What is Reactivity Series?
An order of metals arranged by how readily each one loses electrons to form a positive ion, with the most reactive at the top. Carbon and hydrogen are included as non-metal reference points: carbon marks the boundary for extraction method and hydrogen marks the boundary for reaction with dilute acids.
This definition is part of the Metals chapter in Cambridge O Level Chemistry.
Reactivity Series in context
Everything in Topic 9 hangs on one chain. A metal is a lattice of positive ions in a sea of delocalised electrons, and that structure gives the physical properties. Those properties decide what each metal is used for. Separately, how readily an atom gives up electrons to become a positive ion decides where the metal sits in the reactivity series — and that one position predicts its reactions with water, steam and acid, whether it displaces another metal, whether it can protect iron from rusting, and how hard it is to pull out of its ore.
Metals are elements whose atoms form a giant lattice of positive ions surrounded by delocalised electrons, which is why they conduct heat and electricity, and can be hammered (malleable) or drawn into wire (ductile) without breaking. The reactivity series orders metals by how readily each one loses electrons to form a positive ion, with carbon and hydrogen included as reference points: a metal above carbon must be extracted by electrolysis, a metal below carbon is extracted by reduction with carbon monoxide, and a metal above hydrogen reacts with dilute acid while one below it does not.
Common mistakes with Reactivity Series
- 6. “Aluminium does not react with water, so it must be low in the reactivity series.” Repair Aluminium is high in the series, above zinc and iron. It behaves as though it were unreactive because a thin, tough, continuous layer of aluminium oxide forms on the surface and stops air and water reaching the metal. Say “oxide layer”, never “low reactivity”. Where Lesson 9.4E.
- 15. “Copper does not react with dilute acid because it has a protective oxide layer.” Defect Borrows aluminium’s explanation for a metal that does not need one. Reason Copper genuinely is unreactive towards dilute acid, because it sits below hydrogen. No barrier is involved. Repair “Copper is below hydrogen in the reactivity series, so it cannot displace hydrogen from the acid.” Transfer Which metal does need the oxide-layer explanation, and why? Aluminium — because its position predicts a reaction that is not observed.
Examiner tips on Reactivity Series
- How to write a no-reaction answer. “Nothing happens” scores nothing. “No reaction, because copper is below hydrogen in the reactivity series, so it cannot displace hydrogen from the acid” scores the marks. The reason is the answer; the observation is only the evidence.
- If a session goes badly. Do not restart the chapter. Identify which check failed — the mastery table gives you the code — and re-read only the lesson that owns it. Topic 9 is unusually well suited to this, because almost every failure traces back to one specific position in the reactivity series.
Questions students ask about Reactivity Series
Why does aluminium seem unreactive even though it is high in the reactivity series?
Aluminium reacts instantly with air to form a thin, tough, continuous layer of aluminium oxide on its surface. This layer stops air and water reaching the metal underneath, so the aluminium appears unreactive, even though it sits above zinc and iron in the reactivity series. The correct explanation names the oxide layer, never "low reactivity".
How do you predict whether one metal will displace another from solution?
Compare the two metals' positions in the reactivity series: a more reactive metal displaces a less reactive one from a solution of its ions, because it loses electrons more readily. Zinc is above copper, so zinc displaces copper from copper(II) sulfate solution, the blue colour fades, and a red-brown solid of copper coats the zinc. Displacement only runs downhill, so copper cannot displace iron.