AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
The reactivity series: explain how the reactivity of metals with water or dilute acids is related to the tendency of the metal to form its positive ion
A metal's reactivity with water or dilute acid depends on how readily its atoms lose electrons to form positive ions.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A metal's reactivity with water or dilute acid depends on how readily its atoms lose electrons to form positive ions. Metals high in the reactivity series, such as potassium, sodium, calcium and magnesium, have atoms that lose outer-shell electrons easily, so they form positive ions readily and react vigorously. For example, sodium reacts rapidly with cold water, producing sodium ions, Na⁺, and hydrogen gas. Metals low in the series, such as copper, silver and gold, hold their electrons more strongly, form positive ions only with difficulty, and therefore react slowly or not at all. When a metal reacts, it is oxidised: M → Mⁿ⁺ + n e⁻. The greater the tendency to form positive ions, the more reactive the metal and the more vigorous its reaction with water or dilute acid.
What earns the marks
- Reactivity is linked to the ease with which a metal atom loses one or more electrons to form a positive ion.
- A metal that forms positive ions readily, such as sodium forming Na⁺, is described as reactive and reacts vigorously with water or dilute acid.
- A metal that forms positive ions only with difficulty, such as copper forming Cu²⁺, is unreactive and reacts slowly or not at all with water or dilute acid.
- The reaction with water or dilute acid involves the metal being oxidised, for example M → Mⁿ⁺ + n e⁻, and the observation of bubbles, heat or a metal salt solution supports the link to ion formation.
Common mistakes and how to put them right
Saying that reactivity depends on the metal's density or melting point.
Put it right: Reactivity depends on the tendency of the metal atom to lose electrons and form a positive ion, not on physical properties such as density.
Writing that a reactive metal gains electrons to form a positive ion.
Put it right: A positive ion forms when a metal atom loses electrons, for example Na → Na⁺ + e⁻.
Stating that copper reacts vigorously with cold water because it is a metal.
Put it right: Copper is low in the reactivity series, forms positive ions only with difficulty, and does not react with cold water or dilute acid under normal laboratory conditions.
Exam tips
- When explaining reactivity, always name the metal ion formed and state that the metal atom loses electrons, for example magnesium forms Mg²⁺ by losing two electrons.
- Link your explanation to a specific observation, such as the rate of bubbling or temperature rise, to show how the tendency to form positive ions is demonstrated experimentally.
- Use the reactivity series to justify your answer: place the metal in the series and state whether it is above or below hydrogen, then explain what that means for its reaction with water or dilute acid.
Try the lesson
The start of the The reactivity series: explain how the reactivity of metals with water or dilute acids is related to the tendency of the metal to form its positive ion lesson, made from checked teaching notes for this specification point.
Have a go first
Potassium reacts very vigorously with cold water, while copper does not react with cold water at all. What does this difference show about how easily each metal forms its positive ion?
Listen
A metal's reactivity with water or dilute acid depends on how readily its atoms lose electrons to form positive ions. Metals high in the reactivity series, such as potassium, sodium, calcium and magnesium, have atoms that lose outer-shell electrons easily, so they form positive ions readily and react vigorously. For example, sodium reacts rapidly with cold water, producing sodium ions, Na⁺, and hydrogen gas. Metals low in the series, such as copper, silver and gold, hold their electrons more strongly, form positive ions only with difficulty, and therefore react slowly or not at all. When a metal reacts, it is oxidised: M → Mⁿ⁺ + n e⁻. The greater the tendency to form positive ions, the more reactive the metal and the more vigorous its reaction with water or dilute acid. A strong answer earns marks for these points. Reactivity is linked to the ease with which a metal atom loses one or more electrons to form a positive ion. A metal that forms positive ions readily, such as sodium forming Na⁺, is described as reactive and reacts vigorously with water or dilute acid. A metal that forms positive ions only with difficulty, such as copper forming Cu²⁺, is unreactive and reacts slowly or not at all with water or dilute acid. The reaction with water or dilute acid involves the metal being oxidised, for example M → Mⁿ⁺ + n e⁻, and the observation of bubbles, heat or a metal salt solution supports the link to ion formation. A common slip: saying that reactivity depends on the metal's density or melting point. Instead, reactivity depends on the tendency of the metal atom to lose electrons and form a positive ion, not on physical properties such as density. Exam tip: When explaining reactivity, always name the metal ion formed and state that the metal atom loses electrons, for example magnesium forms Mg²⁺ by losing two electrons.
Key words
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Reactivity series
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Ion formation
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Oxidation and electron loss
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Experimental observation of metal reactions
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See every definition
- Reactivity series
- An order in which metals are placed according to their tendency to form positive ions, so that a metal higher in it reacts more vigorously with water or dilute acid.
- Ion formation
- The process in which a metal atom loses one or more electrons to form a positive ion, which happens readily in reactive metals and only with difficulty in unreactive ones.
- Oxidation and electron loss
- When a metal reacts it is oxidised, written as M → Mⁿ⁺ + n e⁻, so the metal atom loses electrons as it forms its positive ion.
- Experimental observation of metal reactions
- Bubbles, heat or a metal salt solution seen when a metal reacts with water or dilute acid, supporting the link between the reaction and ion formation.
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