1. What Is the Reactivity Series?

What Is the Reactivity Series?

Metals do not all react in the same way. Some metals react extremely quickly with substances such as water and acids, while others react slowly or may show little obvious reaction under the same conditions.

The reactivity series is a list that places metals in order according to how readily they undergo chemical reactions.

A metal near the top of the series is generally more reactive.

A metal near the bottom is generally less reactive.

Chemists use the reactivity series to predict reactions involving metals, including reactions with:

• water
• acids
• oxygen
• metal compounds

It is also useful for predicting displacement reactions and understanding how metals can be extracted from their ores.

The Reactivity Series

A commonly used version of the reactivity series is:

Most reactive

Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminium
Carbon
Zinc
Iron
Hydrogen
Copper
Silver
Gold

Least reactive

Carbon and hydrogen are included as useful reference points even though they are not metals.

Different courses may include additional metals such as tin, lead or platinum, but the general pattern is the same.

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What Does "Reactive" Mean?

A reactive metal readily takes part in chemical reactions.

At the particle level, metal atoms react by losing electrons and forming positive ions.

For example:

Mg → Mg²⁺ + 2e⁻

Magnesium atoms lose electrons relatively readily.

Copper atoms are less willing to lose electrons under similar conditions.

Therefore, magnesium is placed above copper in the reactivity series.

In general:

More reactive metal → loses electrons more readily

This idea becomes especially important when studying redox reactions and electrochemistry.

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Why Is the Reactivity Series Useful?

The reactivity series allows us to make predictions without having to test every possible reaction.

If we know where a metal appears in the series, we can often predict:

• whether it will react with water
• whether it will react with dilute acids
• how vigorous a reaction may be
• whether it can displace another metal
• whether it can be extracted using carbon
• how easily it may corrode

The series is therefore a powerful predictive tool.

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Comparing Highly Reactive and Unreactive Metals

Consider potassium and gold.

Potassium is extremely reactive. It readily reacts with substances in its environment and is not normally found naturally as pure potassium metal.

Gold is much less reactive. It can remain chemically unchanged for long periods and can occur naturally in its elemental form.

This difference helps explain why gold has historically been useful for jewellery and valuable objects.

How Is the Reactivity Series Determined?

The reactivity series is based on experimental evidence.

Scientists can compare how different metals behave under similar conditions.

Useful experiments include reactions between metals and:

• water
• steam
• dilute acids
• oxygen
• solutions containing ions of other metals

Scientists compare observations such as:

• whether a reaction occurs
• how quickly it occurs
• production of gas
• temperature changes
• colour changes
• formation of new substances

Repeated evidence allows metals to be placed in a consistent order.

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Metals Reacting with Water

Water is one way of comparing metal reactivity.

Some highly reactive metals react strongly with cold water.

For example, sodium reacts readily with water.

A simplified word equation is:

sodium + water → sodium hydroxide + hydrogen

Calcium also reacts with cold water:

calcium + water → calcium hydroxide + hydrogen

Less reactive metals may react only with steam, while still less reactive metals may not react significantly with water under ordinary conditions.

A General Pattern with Water

A simplified pattern is:

Potassium, Sodium and Lithium

React strongly with cold water.

Calcium

Reacts with cold water, generally less violently than potassium or sodium.

Magnesium

Reacts only slowly with cold water but more readily with steam.

Zinc and Iron

Do not react significantly with cold water but can react with steam under suitable conditions.

Copper, Silver and Gold

Do not normally react with water.

The exact reaction conditions matter, so the reactivity series should be used together with knowledge of the substance and conditions involved.

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Observing Reactivity with Water

Suppose equal-sized pieces of different metals are placed in water under controlled conditions.

Possible observations might include:

Metal A: vigorous bubbling and rapid movement

Metal B: slower bubbling

Metal C: no obvious reaction

These observations provide evidence that:

Metal A is more reactive than Metal B

and:

Metal B is more reactive than Metal C

To make this comparison fair, variables such as metal amount, water volume and temperature should be controlled.

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Metals Reacting with Acids

Dilute acids are another useful way to compare metal reactivity.

Many metals react with dilute acids to produce:

metal + acid → salt + hydrogen

For example:

magnesium + hydrochloric acid → magnesium chloride + hydrogen

Symbol equation:

Mg + 2HCl → MgCl₂ + H₂

Hydrogen gas is often observed as bubbles.

A faster production of hydrogen under comparable conditions usually indicates a faster reaction.

Metals Above Hydrogen

Hydrogen is included in the reactivity series as a reference point.

Metals above hydrogen can generally displace hydrogen from suitable dilute acids.

For example:

Magnesium is above hydrogen.

Therefore:

magnesium + hydrochloric acid → magnesium chloride + hydrogen

Zinc is also above hydrogen:

zinc + hydrochloric acid → zinc chloride + hydrogen

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Metals Below Hydrogen

Metals below hydrogen generally do not displace hydrogen from common dilute non-oxidizing acids such as dilute hydrochloric acid.

Copper is below hydrogen.

Therefore, copper does not normally react with dilute hydrochloric acid to release hydrogen.

So:

copper + dilute hydrochloric acid → no reaction

Silver and gold are also below hydrogen.

This gives us a useful rule:

Metal above hydrogen → can generally produce hydrogen with suitable dilute acid

Metal below hydrogen → generally cannot

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Comparing Magnesium, Zinc and Iron with Acid

Suppose equal pieces of magnesium, zinc and iron are added separately to equal volumes of dilute hydrochloric acid of the same concentration.

You might observe:

Magnesium

Rapid bubbling.

Zinc

Moderate bubbling.

Iron

Slower bubbling.

This provides experimental evidence for the order:

magnesium > zinc > iron

in the reactivity series.

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Making a Fair Comparison

When comparing metals experimentally, conditions should be controlled.

For example, keep the following the same:

• mass of metal
• surface area of metal
• volume of acid
• concentration of acid
• temperature
• apparatus
• measurement method

If one metal is powdered while another is a large lump, the comparison would not be fair because surface area affects reaction rate.

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Metals Reacting with Oxygen

Metals can also react with oxygen to form metal oxides.

General word equation:

metal + oxygen → metal oxide

For example:

magnesium + oxygen → magnesium oxide

Symbol equation:

2Mg + O₂ → 2MgO

Magnesium burns strongly when heated in oxygen, producing an intense white light.

Reactivity and Oxygen

Different metals react with oxygen at different rates and under different conditions.

Some metals oxidize extremely readily.

Others react only when heated.

Some very unreactive metals resist oxidation.

This provides another source of evidence for the reactivity series.

However, reaction rate alone must be interpreted carefully because protective oxide layers can affect what we observe.

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Aluminium: An Interesting Example

Aluminium is relatively high in the reactivity series, yet aluminium objects often appear surprisingly resistant to corrosion.

Why?

Aluminium quickly reacts with oxygen to form a thin layer of aluminium oxide on its surface.

This oxide layer is strongly attached and protects the metal underneath from further reaction.

Therefore, the apparent behaviour of a metal does not always reveal its underlying reactivity immediately.

This is an important reminder:

observed reaction rate can be affected by surface conditions.

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Displacement Reactions

One of the most useful applications of the reactivity series is predicting displacement reactions.

A more reactive metal can displace a less reactive metal from a solution containing its ions.

General pattern:

more reactive metal + less reactive metal compound → more reactive metal compound + less reactive metal

For example:

zinc + copper sulfate → zinc sulfate + copper

Symbol equation:

Zn + CuSO₄ → ZnSO₄ + Cu

This happens because zinc is more reactive than copper.

Predicting a Displacement Reaction

Suppose magnesium metal is placed into copper sulfate solution.

Check the reactivity series:

magnesium is above copper

Therefore, magnesium is more reactive.

Magnesium can displace copper:

magnesium + copper sulfate → magnesium sulfate + copper

Symbol equation:

Mg + CuSO₄ → MgSO₄ + Cu

Copper metal is produced.

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When No Displacement Occurs

Now place copper metal into magnesium sulfate solution.

Check the series:

copper is below magnesium

Copper is less reactive.

Therefore, copper cannot displace magnesium.

So:

copper + magnesium sulfate → no reaction

This gives us the displacement rule:

A metal can displace a metal below it in the reactivity series.

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Worked Example: Iron and Copper Sulfate

Question:

Will iron react with copper sulfate?

Locate the metals:

iron is above copper

Therefore, iron is more reactive.

So iron can displace copper.

Word equation:

iron + copper sulfate → iron sulfate + copper

Symbol equation:

Fe + CuSO₄ → FeSO₄ + Cu

Copper metal is deposited while iron enters the solution as iron ions.

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Worked Example: Silver and Zinc Sulfate

Question:

Will silver react with zinc sulfate?

Compare the metals:

zinc is above silver

Therefore, silver is less reactive.

Silver cannot displace zinc.

So:

silver + zinc sulfate → no reaction

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Building the Reactivity Series Using Displacement Reactions

Imagine three unknown metals:

A, B and C.

Experiments show:

• A displaces B from a solution of B ions.
• A displaces C from a solution of C ions.
• B displaces C from a solution of C ions.

From the first observation:

A > B

From the second:

A > C

From the third:

B > C

Therefore:

A > B > C

Displacement experiments can therefore be used to construct a reactivity order even when the metals are initially unknown.

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Reactivity and Electron Transfer

Why can zinc displace copper?

Consider:

Zn + Cu²⁺ → Zn²⁺ + Cu

Zinc atoms lose electrons:

Zn → Zn²⁺ + 2e⁻

Copper ions gain those electrons:

Cu²⁺ + 2e⁻ → Cu

Overall:

Zn + Cu²⁺ → Zn²⁺ + Cu

Zinc is more reactive because it has a greater tendency than copper to form positive ions under these conditions.

This is a redox reaction.

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Oxidation and Reduction

Metal displacement reactions involve electron transfer.

Oxidation

Loss of electrons.

For zinc:

Zn → Zn²⁺ + 2e⁻

Zinc is oxidized.

Reduction

Gain of electrons.

For copper ions:

Cu²⁺ + 2e⁻ → Cu

Copper ions are reduced.

A useful memory aid is:

OIL RIG

Oxidation Is Loss

Reduction Is Gain

This refers to electrons.

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Why Is Carbon in the Reactivity Series?

Carbon is not a metal, but it is included because it is useful when considering metal extraction.

Some metal oxides can be reduced using carbon.

Metals below carbon in the series can often be extracted from their oxides by heating with carbon or carbon monoxide.

For example, iron is below carbon.

This is why carbon-based reduction can be used in iron extraction.

Metals above carbon are generally too reactive to be extracted from their compounds this way.

Extracting Very Reactive Metals

Metals high in the reactivity series form very stable compounds.

For metals such as:

• potassium
• sodium
• lithium
• calcium
• magnesium
• aluminium

carbon reduction is generally not suitable.

These metals may be extracted using electrolysis of molten ionic compounds.

Electrolysis requires electrical energy, which can make extraction more energy-intensive.

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Reactivity and Natural Occurrence

Highly reactive metals are rarely found naturally as pure elements because they readily react with other substances.

Instead, they are usually found in compounds.

For example, sodium commonly occurs in compounds such as sodium chloride rather than as sodium metal.

Less reactive metals are more likely to occur naturally in an uncombined state.

Gold is a famous example.

This helps explain why humans discovered and used some less reactive metals very early in history.

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Reactivity and Corrosion

The reactivity series can also help us understand corrosion.

Iron reacts with oxygen and water to form rust.

Gold is much less reactive and resists corrosion.

However, corrosion behaviour is more complicated than simply reading the reactivity series because factors such as:

• protective oxide layers
• water
• oxygen
• salts
• temperature
• coatings

can affect corrosion rates.

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Sacrificial Protection

The reactivity series can be used to protect iron and steel.

Suppose iron is connected to a more reactive metal such as zinc.

Because zinc is more reactive, zinc can oxidize preferentially.

This helps protect the iron.

This method is called sacrificial protection.

It is used in situations involving steel structures, pipelines and some marine applications.

Galvanizing

Iron or steel can also be protected by coating it with zinc.

This process is called galvanizing.

The zinc coating:

• forms a physical barrier
• reduces contact between iron, oxygen and water
• can provide sacrificial protection if the coating is damaged

The usefulness of zinc is directly related to its position above iron in the reactivity series.

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Predicting Reactions Systematically

When faced with a reactivity-series question, use the following approach.

Identify the substances.

Determine which metals are involved.

Locate the metals in the series.

Remember:

higher = more reactive

Identify the type of reaction.

Is it:

• metal + water?
• metal + acid?
• metal + metal compound?
• metal extraction?

Apply the appropriate rule.

For displacement:

higher metal displaces lower metal

For common dilute acids:

metal above hydrogen generally releases hydrogen

For carbon extraction:

many metals below carbon can be reduced from their oxides using carbon

Write the products.

Use the reaction pattern to predict what forms.

Check the equation.

If a symbol equation is required, ensure it is correctly balanced.

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Worked Prediction Table

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Evidence from Several Experiments

No single test is ideal for every metal.

Very reactive metals may be unsafe or impractical to compare using acids.

Very unreactive metals may show little reaction with water or dilute acids.

Scientists therefore use multiple types of evidence.

For example:

• reaction with water
• reaction with acids
• displacement reactions
• reactions with oxygen
• electrochemical measurements

Together, these observations provide a consistent picture of relative metal reactivity.

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Common Mistakes

Thinking the Bottom Is Most Reactive

The usual convention is:

top = more reactive

bottom = less reactive

Thinking Carbon and Hydrogen Are Metals

They are not.

They are included as useful reference points.

Thinking Every Metal Reacts with Dilute Acid

Metals below hydrogen generally do not release hydrogen from common dilute non-oxidizing acids.

Thinking a Less Reactive Metal Can Displace a More Reactive Metal

It cannot.

More reactive displaces less reactive.

Confusing Reaction Rate with Reactivity

Reaction speed provides useful evidence, but factors such as temperature, concentration, surface area and oxide coatings can also affect rate.

Forgetting About Aluminium's Oxide Layer

Aluminium is reactive but often appears resistant because its surface oxide protects it.

Assuming No Visible Change Always Means Nothing Happened

Some reactions may be slow or difficult to observe directly.

Forgetting Experimental Controls

Different surface areas, temperatures or concentrations can make comparisons unfair.

Thinking Carbon Can Extract Every Metal

Carbon is generally useful for metals below it in the reactivity series.

Thinking More Reactive Metals Gain Electrons More Easily

Metals characteristically react by losing electrons to form positive ions.

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Key Terms

Reactivity — A measure of how readily a substance undergoes chemical reactions.

Reactivity series — An ordering of metals according to their relative chemical reactivity.

Reactive metal — A metal that readily undergoes chemical reactions.

Unreactive metal — A metal that reacts relatively slowly or under more restricted conditions.

Displacement reaction — A reaction in which a more reactive element replaces a less reactive element in a compound.

Metal ion — A positively charged ion formed when a metal atom loses electrons.

Oxidation — Loss of electrons.

Reduction — Gain of electrons.

Redox reaction — A reaction involving both oxidation and reduction.

Electron transfer — Movement of electrons from one species to another during a reaction.

Hydrogen — A non-metal included in the reactivity series as a reference for predicting reactions of metals with suitable dilute acids.

Carbon — A non-metal included as a reference when considering extraction of metals.

Metal oxide — A compound containing a metal chemically combined with oxygen.

Salt — An ionic compound that can be produced in reactions involving acids.

Hydrogen gas — H₂, commonly produced when suitable metals react with dilute acids.

Corrosion — Chemical deterioration of a material through reactions with its environment.

Rusting — Corrosion of iron involving oxygen and water.

Sacrificial protection — Protection of a metal using a more reactive metal that oxidizes preferentially.

Galvanizing — Coating iron or steel with zinc to help prevent corrosion.

Extraction — The process of obtaining a useful metal from its compounds or ores.

Ore — Naturally occurring material containing sufficient quantities of a substance for extraction to be worthwhile.

Electrolysis — The use of electrical energy to drive chemical changes, including extraction of some reactive metals.

Oxide layer — A layer of metal oxide formed on the surface of a metal.

Passivation — Formation of a protective surface layer that slows further reaction.

Control variable — A factor kept constant during an experiment so that comparisons are valid.

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Key Takeaways

• The reactivity series ranks metals according to their relative chemical reactivity.
• Metals near the top are generally more reactive.
• Metals near the bottom are generally less reactive.
• Reactive metals tend to lose electrons readily and form positive ions.
• The reactivity series is based on experimental evidence.
• Reactions with water can provide evidence about metal reactivity.
• Reactions with dilute acids can also be used to compare metals.
• Metals above hydrogen generally react with suitable dilute acids to release hydrogen.
• Metals below hydrogen generally do not displace hydrogen from common dilute non-oxidizing acids.
• Displacement reactions provide an important method for comparing metal reactivity.
• A more reactive metal can displace a less reactive metal from a compound.
• A less reactive metal cannot displace a more reactive metal.
• Metal displacement reactions involve electron transfer.
• Oxidation is loss of electrons.
• Reduction is gain of electrons.
• Carbon is included as a reference even though it is not a metal.
• Hydrogen is also included as a reference even though it is not a metal.
• The position of carbon helps predict possible methods of metal extraction.
• Many metals below carbon can be extracted from their oxides using carbon or carbon monoxide.
• Very reactive metals may require electrolysis for extraction.
• Highly reactive metals are usually found naturally in compounds rather than as pure elements.
• Very unreactive metals such as gold may occur naturally in elemental form.
• The reactivity series can help explain corrosion and methods of corrosion protection.
• Zinc can protect iron because zinc is more reactive than iron.
• Aluminium demonstrates that observable reaction rate can be affected by a protective oxide layer.
• Experimental comparisons must control variables such as surface area, concentration and temperature.
• The reactivity series allows chemists to predict reactions before carrying them out.

The most important rule for displacement reactions is:

More reactive metal + less reactive metal compound → displacement occurs

Or, even more simply:

A metal can displace metals below it in the reactivity series.

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Check Your Understanding

1. What is the reactivity series?

2. What does it mean if one metal is above another metal in the series?

3. Arrange these metals from most reactive to least reactive:

copper, magnesium, gold, zinc, iron

4. Why are hydrogen and carbon included even though they are not metals?

5. Describe one experiment that could be used to compare the reactivity of metals.

6. Why must surface area be controlled when comparing reactions?

7. Predict whether magnesium will react with dilute hydrochloric acid.

8. Write the word equation for magnesium reacting with hydrochloric acid.

9. Why does copper not normally produce hydrogen with dilute hydrochloric acid?

10. Which would you expect to react more vigorously with dilute acid: magnesium or iron? Explain.

11. Predict whether zinc will displace copper from copper sulfate.

12. Write the word equation for this reaction.

13. Write the balanced symbol equation for this reaction.

14. Predict whether copper will displace zinc from zinc sulfate. Explain.

15. Iron is placed into copper sulfate solution. Predict what happens and explain your reasoning.

16. Silver is placed into magnesium sulfate solution. Predict whether a reaction occurs.

17. Unknown metal A displaces metal B. What can you conclude about their relative reactivities?

18. Metal B displaces metal C. If A also displaces C, arrange A, B and C in order of decreasing reactivity.

19. Explain why highly reactive metals are rarely found naturally as pure elements.

20. Why can gold sometimes occur naturally in elemental form?

21. Explain why aluminium can appear less reactive than expected.

22. What is oxidation in terms of electrons?

23. What is reduction in terms of electrons?

24. In the reaction:

Zn + Cu²⁺ → Zn²⁺ + Cu

which substance is oxidized?

25. Which substance is reduced?

26. Why is carbon important when considering metal extraction?

27. Why are very reactive metals often extracted using electrolysis?

28. Explain how zinc can protect iron from corrosion.

29. Give two experimental variables that should be controlled when comparing metal reactions with acids.

30. Challenge: Four unknown metals, W, X, Y and Z, are tested.

• W displaces X from a solution of X ions.
• X displaces Y.
• Z displaces W.
• Y cannot displace X.
• W cannot displace Z.

a. Which metal is most reactive?
b. Which metal is least reactive?
c. Arrange all four metals from most reactive to least reactive.
d. Would Z displace X? Explain.
e. Would Y displace W? Explain.
f. Which metal would lose electrons most readily based on these observations?
g. Explain how the displacement results provide evidence for your ordering.
h. Suggest another experiment that could provide additional evidence for the relative reactivities.
i. Identify two variables that should be controlled in your proposed experiment.
j. Explain why using several different experiments can give greater confidence in a reactivity series.