Caesium (Cs) is an alkali metal in Group 1 of the periodic table, below potassium. State and explain two properties of caesium that you would expect based on its position in Group 1, compared to the alkali metals above it.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Caesium is a soft, silvery-white alkali metal. It is element 55 and sits near the bottom of Group 1 of the periodic table.
Model answer (4 marks)
Caesium has a lower melting point than the alkali metals above it.
Melting point decreases down Group 1 because the metallic bonds become weaker as the atomic/ionic radius increases.
Caesium is more reactive than the alkali metals above it.
Reactivity increases down Group 1 because the outer electron is further from the nucleus and is lost more easily, so caesium loses its outer electron more readily.
Melting point decreases down Group 1 because the metallic bonds become weaker as the atomic/ionic radius increases.
Caesium is more reactive than the alkali metals above it.
Reactivity increases down Group 1 because the outer electron is further from the nucleus and is lost more easily, so caesium loses its outer electron more readily.
Examiner tips
- Use the exact terms ‘lower melting point’ and ‘more reactive’.
- Explain the trend in terms of atomic/ionic radius and electron loss.
- Show the comparison with a metal above (e.g. potassium).
Common mistakes
- Confusing melting point with boiling point.
- Saying ‘caesium is less reactive’ or not linking reactivity to electron distance.
Mark scheme (4 marks)
- Caesium has a lower melting point than the alkali metals above it (e.g. lower than sodium or potassium)
- Melting point decreases down Group 1 because the metallic bonds become weaker as atomic/ionic radius increases
- Caesium is more reactive than the alkali metals above it (e.g. more reactive than potassium/sodium/lithium)
- Reactivity increases down Group 1 because the outer electron is further from the nucleus / lost more easily, so caesium loses its outer electron more readily
Key terms in this question
Related
- All Pearson Edexcel International GCSE Chemistry (4CH1) revision notes →
- How to answer a "State and explain" question →
- Decode the mark scheme abbreviations →
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