Revision notes for AQA GCSE Chemistry The reactivity series. Open the guide for explanations and worked examples. Written against the AQA GCSE Chemistry (8462) specification, so the content matches what's examinable rather than general Chemistry background.
The reactivity series
Welcome to the reactivity series! In this topic, you will learn:
- What makes one metal more reactive than another at an atomic level.
- How to memorise the order of the reactivity series.
- How to predict the reactions of metals with water and dilute acids.
- How to use experimental clues to deduce a metal's position in the series.
What makes a metal reactive?
Before we look at the list of metals, we need to understand what "reactivity" actually means for a metal.
When metals react with other substances, their atoms lose outer electrons to form positive ions. For example, when sodium reacts, its atoms lose one electron to form Na+\text{Na}^+Na+ ions.
Definition
Reactivity
For a metal, reactivity is a measure of its tendency to lose electrons and form positive ions.
If a metal loses its outer electrons very easily, it forms positive ions readily and is described as a highly reactive metal. If a metal holds tightly onto its outer electrons, it is less reactive.
Key Idea
Forming Positive Ions
The golden rule of metal chemistry: the easier it is for a metal to form a positive ion, the more reactive the metal is.
The Reactivity Series
We can arrange metals in a list from the most reactive down to the least reactive. This list is called the reactivity series.
Based on their reactions, the required metals for your specification are ranked as follows:
- Potassium (K)
- Sodium (Na)
- Lithium (Li)
- Calcium (Ca)
- Magnesium (Mg)
- Zinc (Zn)
- Iron (Fe)
- Copper (Cu)
You will also often see two non-metals, carbon and hydrogen, slotted into this list.
Tip
The Non-Metals
Why include non-metals in a list of metals? Carbon and hydrogen are placed in the series as useful "reference points". Knowing whether a metal is above or below carbon tells us how we can extract it from its ore, and knowing whether it is above or below hydrogen tells us if it will react with dilute acids!
Here is how the complete series looks:
Reactions with Water and Acids
We can prove the order of the reactivity series by testing metals against cold water and dilute acids (at room temperature).
Reactions with water
Only the most reactive metals (those at the very top of the series) will react with cold water. When they do, they produce a metal hydroxide and hydrogen gas.
Metal + Water →\to→ Metal hydroxide + Hydrogen
- Potassium, Sodium, and Lithium react vigorously with cold water. They fizz rapidly (releasing hydrogen gas) and dissolve to form alkaline hydroxide solutions.
- Calcium reacts safely but still quite quickly, bubbling and forming a cloudy white mixture (calcium hydroxide is not very soluble).
If we write out the balanced symbol equation for sodium reacting with water, it looks like this:
2Na(s)+2H2O(l)→2NaOH(aq)+H2(g)\text{2Na(s)} + \text{2H}_2\text{O(l)} \to \text{2NaOH(aq)} + \text{H}_2\text{(g)}2Na(s)+2H2O(l)→2NaOH(aq)+H2(g)Reactions with dilute acids
Metals that are slightly lower down the series won't react with cold water, but they are still reactive enough to react with dilute acids (like hydrochloric acid or sulfuric acid). This reaction produces a metal salt and hydrogen gas.
Metal + Acid →\to→ Metal salt + Hydrogen
- Magnesium, Zinc, and Iron react with dilute acids. Magnesium reacts vigorously, zinc reacts steadily, and iron reacts very slowly.
- You can tell the speed of the reaction by observing the rate at which bubbles of hydrogen gas are given off.
Here is the balanced symbol equation for magnesium reacting with dilute hydrochloric acid:
Mg(s)+2HCl(aq)→MgCl2(aq)+H2(g)\text{Mg(s)} + \text{2HCl(aq)} \to \text{MgCl}_2\text{(aq)} + \text{H}_2\text{(g)}Mg(s)+2HCl(aq)→MgCl2(aq)+H2(g)Copper, sitting right at the bottom of our list, is completely unreactive with cold water and dilute acids. It is safely used in household plumbing for exactly this reason!
Displacement Reactions
Because metals have different reactivities, they can compete with each other.
A more reactive metal will displace (push out) a less reactive metal from a compound. It does this because the more reactive metal has a stronger drive to form positive ions than the less reactive one.
For example, if you place a piece of magnesium into a blue solution of copper sulfate, the magnesium displaces the copper. The solution turns colourless (forming magnesium sulfate) and reddish-brown bits of solid copper metal appear:
Mg(s)+CuSO4(aq)→MgSO4(aq)+Cu(s)\text{Mg(s)} + \text{CuSO}_4\text{(aq)} \to \text{MgSO}_4\text{(aq)} + \text{Cu(s)}Mg(s)+CuSO4(aq)→MgSO4(aq)+Cu(s)If you tried this the other way around — putting solid copper into magnesium sulfate — absolutely nothing would happen, because copper is less reactive than magnesium.
Example
Deducing reactivity from experimental results
You are given three unknown metals: Metal X, Metal Y, and Metal Z.
- Metal X does not react with water or dilute acid.
- Metal Y fizzes gently in dilute hydrochloric acid, but does not react with cold water.
- Metal Z fizzes violently in cold water.
Deduce the order of reactivity for these three metals, from most reactive to least reactive.
- Analyse the water reaction: Cold water only reacts with the most highly reactive metals. Since Metal Z fizzes violently in water, it must be the most reactive of the three.
- Analyse the acid reaction: Dilute acids react with metals that are moderately reactive (but not reactive enough to tackle cold water). Metal Y does not react with water but does react with acid, so it sits in the middle.
- Identify the unreactive metal: Metal X ignores both water and acid, meaning it cannot readily form positive ions under these conditions. This makes it the least reactive (likely sitting below hydrogen in the reactivity series, like copper).
- State the final order: From most to least reactive, the order is Z, Y, X.
Exam technique
In the exam
- Learn the list: Make up a mnemonic to remember the exact order of the 8 specification metals, plus carbon and hydrogen.
- Look for hydrogen: If a question describes a metal reacting with an acid to produce bubbles, those bubbles are hydrogen gas. You can test for this gas using a lit splint, which will produce a "squeaky pop".
- Use state symbols: When writing equations for these reactions, remember that the metal goes in as a solid
(s), the acid is aqueous(aq), the resulting salt is aqueous(aq), and the hydrogen produced is a gas(g).
Self review
Check yourself
- What happens to the electrons of a metal atom when it reacts?
- Which two non-metals are commonly included in the reactivity series?
- What are the two products formed when calcium reacts with cold water?
- Will iron displace zinc from a solution of zinc sulfate? Why or why not?
Reactivity of metals
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