AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Students should be able to describe the reactions of the first three…
Full specification wording
Group 1: Students should be able to describe the reactions of the first three alkali metals with oxygen, chlorine and water.
The first three alkali metals are lithium, sodium and potassium.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 2 of 4
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The first three alkali metals are lithium, sodium and potassium. With oxygen, they burn in air to form metal oxides, for example lithium oxide, Li₂O, sodium oxide, Na₂O, and potassium oxide, K₂O; sodium and potassium may also form peroxides or superoxides, but the oxide is the expected product at this level. With chlorine, they burn to form white metal chlorides such as lithium chloride, LiCl, sodium chloride, NaCl, and potassium chloride, KCl. With water, they produce a metal hydroxide and hydrogen gas, for example 2Na + 2H₂O → 2NaOH + H₂. Reactivity increases from lithium to sodium to potassium, so potassium reacts most vigorously, often igniting the hydrogen produced.
What earns the marks
- Names the first three alkali metals as lithium, sodium and potassium.
- Describes the reaction with oxygen to form a metal oxide, giving a correct example such as 4Na + O₂ → 2Na₂O.
- Describes the reaction with chlorine to form a white metal chloride, giving a correct example such as 2Na + Cl₂ → 2NaCl.
- Describes the reaction with water to form a metal hydroxide and hydrogen, giving a correct example such as 2K + 2H₂O → 2KOH + H₂.
- States that reactivity increases from lithium to sodium to potassium, so potassium reacts most vigorously.
- Describes observations such as fizzing, movement on the water surface and the metal becoming smaller.
Common mistakes and how to put them right
Writing hydrogen as the only product of the reaction with water.
Put it right by including the metal hydroxide as well.
Balancing equations incorrectly, for example leaving oxygen atoms unequal.
Put it right by checking that each element has the same number of atoms on both sides.
Stating that lithium reacts more vigorously than potassium.
Put it right by ordering reactivity as lithium < sodium < potassium.
Exam tips
- Learn the general word equations for oxygen, chlorine and water before learning specific balanced equations.
- When describing observations, include fizzing, floating, movement and the metal shrinking or disappearing.
- Check balancing by counting atoms of each element on both sides of the equation.
Try the lesson
The start of the Group 1: Students should be able to describe the reactions of the first three alkali metals with oxygen, chlorine and water. lesson, made from checked teaching notes for this specification point.
Have a go first
What is produced when lithium reacts with water?
Listen
The first three alkali metals are lithium, sodium and potassium. With oxygen, they burn in air to form metal oxides, for example lithium oxide, Li₂O, sodium oxide, Na₂O, and potassium oxide, K₂O; sodium and potassium may also form peroxides or superoxides, but the oxide is the expected product at this level. With chlorine, they burn to form white metal chlorides such as lithium chloride, LiCl, sodium chloride, NaCl, and potassium chloride, KCl. With water, they produce a metal hydroxide and hydrogen gas, for example 2Na + 2H₂O → 2NaOH + H₂. Reactivity increases from lithium to sodium to potassium, so potassium reacts most vigorously, often igniting the hydrogen produced. A strong answer earns marks for these points. Names the first three alkali metals as lithium, sodium and potassium. Describes the reaction with oxygen to form a metal oxide, giving a correct example such as 4Na + O₂ → 2Na₂O. Describes the reaction with chlorine to form a white metal chloride, giving a correct example such as 2Na + Cl₂ → 2NaCl. Describes the reaction with water to form a metal hydroxide and hydrogen, giving a correct example such as 2K + 2H₂O → 2KOH + H₂. A common slip: Writing hydrogen as the only product of the reaction with water. Instead, including the metal hydroxide as well. Exam tip: Learn the general word equations for oxygen, chlorine and water before learning specific balanced equations.
Key words
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Reactions of alkali metals
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Trends in reactivity
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Balancing chemical equations
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Observation and description of chemical change
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See every definition
- Reactions of alkali metals
- The first three alkali metals react with oxygen to form metal oxides, with chlorine to form white metal chlorides, and with water to form a metal hydroxide and hydrogen gas.
- Trends in reactivity
- Reactivity increases from lithium to sodium to potassium, so potassium reacts most vigorously, often igniting the hydrogen produced.
- Balancing chemical equations
- Checking that each element has the same number of atoms on both sides, for example counting atoms of each element on both sides of the equation.
- Observation and description of chemical change
- Describing observations such as fizzing, movement on the water surface and the metal becoming smaller.
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