Sodium and caesium are both Group I metals. Compare the physical and chemical properties of sodium and caesium, referring to trends in Group I.

Cambridge International IGCSE Chemistry (0620) — 8.2 Group I properties · Compare · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Caesium has a lower melting point than sodium – melting points decrease down Group I.
Caesium is less dense (and softer) than sodium – density decreases down Group I.
Caesium is more reactive than sodium – reactivity increases down Group I.
Both caesium and sodium react with water to give a hydroxide and hydrogen, but caesium reacts more vigorously.

Examiner tips

Use the word ‘compare’ to list each property side‑by‑side. Mention the trend (down Group I) for each property. Show the reaction with water for both metals.
Use the exact phrases from the mark scheme (e.g. ‘melting points decrease down Group I’).

Common mistakes

Confusing density trend (saying density increases down Group I). Forgetting to mention the water reaction for both metals. Using vague terms like ‘more reactive’ without linking to the trend.

Mark scheme (4 marks)

Caesium has a lower melting point than sodium / melting points decrease down Group I
Caesium is less dense / softer than sodium OR caesium has a lower density than sodium (accept: density decreases down Group I / caesium is softer)
Caesium is more reactive than sodium / reactivity increases down Group I
Both / caesium reacts with water to produce a hydroxide and hydrogen / caesium reacts more vigorously with water than sodium

Key terms in this question

Group I