Explain why elements in Group 1 of the periodic table become more reactive as you go down the group.

Edexcel A-Level Chemistry (9CH0) — 1.2 Periodic table and trends · Explain · 5 marks · View as Markdown

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

Group 1 elements are known as the alkali metals. They all react with water, but the vigour of the reaction increases from lithium at the top to caesium at the bottom of the group.

Model answer (5 marks)

All Group 1 atoms have one electron in their outer shell.

Going down the group the atoms become larger and have more electron shells.

The outer electron is therefore further from the nucleus.

The attraction between the nucleus and the outer electron decreases, so the outer electron is more easily lost.

Because the outer electron is lost more easily, the element is more reactive.

Examiner tips

Use the word ‘because’ to link the decrease in attraction to increased reactivity.
Show the trend of increasing atomic size down the group to justify the weaker attraction.

Common mistakes

Failing to mention the single valence electron in Group 1.
Confusing the trend of reactivity with that of ionisation energy or electronegativity.

Mark scheme (5 marks)

All Group 1 atoms have one electron in their outer shell
Going down the group, the atoms get larger / have more electron shells
The outer electron is further from the nucleus going down the group
The attraction between the nucleus and the outer electron decreases / the outer electron is more easily lost
Because the outer electron is lost more easily, the element is more reactive (links electron loss to increased reactivity)

Key terms in this question

Group 1