At the particle level, every metal's reactivity is a measure of how readily its atoms lose electrons to form positive ions. The reactivity series ranks metals from most to least electron-releasing — and once you hold that mental picture, predicting displacement reactions, writing half equations, and understanding metal extraction all follow from the same underlying principle.
What is the reactivity series?
The reactivity series is a list of metals ordered from most reactive to least reactive, based on how readily each metal loses electrons (is oxidised) to form positive ions. It is built from experimental evidence — how vigorously metals react with water, acid, and oxygen.
| Metal | Symbol | Reacts with cold water? | Reacts with dilute acid? |
|---|---|---|---|
| Potassium | K | Violently (explodes) | Extremely vigorously |
| Sodium | Na | Vigorously | Extremely vigorously |
| Lithium | Li | Briskly | Very vigorously |
| Calcium | Ca | Steadily | Vigorously |
| Magnesium | Mg | Very slowly | Vigorously |
| Aluminium | Al | No (oxide layer) | Slowly (once oxide removed) |
| Zinc | Zn | No | Moderately |
| Iron | Fe | No | Slowly |
| Lead | Pb | No | Very slowly |
| Copper | Cu | No | No |
| Silver | Ag | No | No |
| Gold | Au | No | No |
A useful mnemonic for the order: Please Stop Letting Children Make A Zebra Ill Licking Chocolate Sweets Goldenly.
What is a displacement reaction?
A displacement reaction occurs when a more reactive metal displaces (pushes out) a less reactive metal from a compound — typically a salt solution or a metal oxide. The more reactive metal loses electrons (is oxidised) and forms ions, whilst the metal ions in the compound gain electrons (are reduced) and become metal atoms.
Classic example — iron displacing copper from copper sulfate solution:
iron + copper sulfate → iron sulfate + copper
Fe + CuSO₄ → FeSO₄ + Cu
This works because iron is more reactive than copper — iron more readily loses electrons to become Fe²⁺, forcing Cu²⁺ to gain electrons and deposit as solid copper metal. You can observe this visually: the blue colour of copper sulfate solution fades, and pink-brown copper metal coats the iron.
How do you predict whether a displacement reaction will occur?
Simply compare the positions of the two metals in the reactivity series:
- More reactive metal + salt of less reactive metal → reaction occurs
- Less reactive metal + salt of more reactive metal → no reaction
Examples:
| Metal added | Salt solution | Reaction? | Reason |
|---|---|---|---|
| Zinc | Copper sulfate | Yes | Zinc (higher) displaces copper (lower) |
| Copper | Zinc sulfate | No | Copper (lower) cannot displace zinc (higher) |
| Magnesium | Iron sulfate | Yes | Magnesium (higher) displaces iron (lower) |
| Silver | Copper nitrate | No | Silver (lower) cannot displace copper |
What are half equations and how do you write them?
A half equation shows either the oxidation or the reduction half of a redox reaction separately. Each half equation must be balanced for both atoms and charge.
Worked example — iron displacing copper:
Oxidation half (iron loses electrons):
Fe → Fe²⁺ + 2e⁻
Iron loses 2 electrons to form Fe²⁺ ions. This is oxidation (loss of electrons — OIL from OIL RIG).
Reduction half (copper ions gain electrons):
Cu²⁺ + 2e⁻ → Cu
Copper ions gain 2 electrons to form copper metal. This is reduction (gain of electrons — RIG from OIL RIG).
To write a half equation:
- Write the species on the correct side (ion on left for reduction; metal on left for oxidation)
- Balance atoms of the metal
- Add electrons (e⁻) to balance the charge
- Check: total charge on left = total charge on right
Another example — magnesium reacting with acid:
Oxidation: Mg → Mg²⁺ + 2e⁻
Reduction: 2H⁺ + 2e⁻ → H₂
How is the reactivity series used in metal extraction?
The position of a metal in the reactivity series determines how it is extracted from its ore:
| Reactivity level | Extraction method | Examples |
|---|---|---|
| Very reactive (above carbon) | Electrolysis of molten compound | Potassium, sodium, calcium, magnesium, aluminium |
| Moderate (below carbon but above hydrogen) | Reduction with carbon/coke in a blast furnace | Zinc, iron, lead |
| Unreactive (below hydrogen) | Found native; simple heating or physical separation | Copper, silver, gold, platinum |
Why can't carbon reduce very reactive metals? Carbon can only reduce a metal oxide if carbon is more reactive than the metal — that is, if carbon loses electrons more readily than the metal. Metals above carbon in the reactivity series (potassium, sodium, calcium, magnesium, aluminium) are MORE reactive than carbon, so carbon cannot displace them. Electrolysis (using electrical energy) is required instead.
How does the reactivity series relate to oxidation and reduction?
The reactivity series is, at its core, a measure of a metal's tendency to be oxidised (to lose electrons):
- High reactivity = strong tendency to lose electrons = easily oxidised = readily forms ions
- Low reactivity = weak tendency to lose electrons = hard to oxidise = commonly found as free metals in nature
In a displacement reaction:
- The more reactive metal is oxidised (loses electrons) → goes from metal to ion
- The less reactive metal ion is reduced (gains electrons) → goes from ion to metal
This is why displacement reactions are classified as redox reactions — both oxidation and reduction occur simultaneously.
Frequently asked questions
What is the reactivity series and why does it matter?
The reactivity series is an ordered list of metals from most reactive (potassium) to least reactive (gold), based on how readily each metal loses electrons to form positive ions. It matters because it lets you predict which displacement reactions will occur, choose appropriate extraction methods for metals from their ores, and understand why some metals corrode quickly whilst gold remains untarnished for thousands of years. It is one of the most practically useful organising ideas in GCSE chemistry.
What is the difference between oxidation and reduction in displacement reactions?
In a displacement reaction, the more reactive metal is oxidised — it loses electrons to form positive ions, going from metal to dissolved ion. The less reactive metal ions in solution are reduced — they gain electrons to become neutral metal atoms, depositing as solid metal. Oxidation and reduction always occur together in a redox reaction; you cannot have one without the other. The memory aid OIL RIG (Oxidation Is Loss, Reduction Is Gain of electrons) is the most reliable way to keep these straight.
Why is aluminium extracted by electrolysis even though carbon can reduce many metals?
Aluminium sits above carbon in the reactivity series, meaning aluminium loses electrons more readily than carbon does. Carbon cannot reduce aluminium oxide because aluminium clings more tightly to oxygen than carbon does — the Al₂O₃ bond is stronger than any C-O bond carbon could form. Electrolysis, which uses electrical energy to force the reduction, is powerful enough to extract aluminium from its molten ore (aluminium oxide dissolved in cryolite). This makes aluminium extraction energy-intensive and therefore expensive compared to iron extraction.
What is a displacement reaction in simple terms?
A displacement reaction is when a more reactive metal "pushes out" a less reactive metal from its compound and takes its place. Imagine a more popular student taking the seat of a less popular one — the more reactive metal wins the position. For example, when zinc is added to blue copper sulfate solution, zinc displaces the copper: the blue colour fades as Cu²⁺ ions leave solution, and pink-brown copper metal appears on the surface of the zinc. The driving force is the difference in reactivity — the greater the gap in the reactivity series, the more vigorously the reaction occurs.
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