Elements in the periodic table are arranged in periods and groups. Explain what is meant by the terms 'period' and 'group', and describe how the arrangement of electrons in an atom is related to its position in the periodic table.

Eduqas A-Level Chemistry — 2.1 Periodic table · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

A period is a horizontal row of the periodic table.
Elements in the same period have the same number of electron shells.
A group is a vertical column of the periodic table.
Elements in the same group have similar chemical properties.
Elements in the same group have the same number of electrons in their outer shell.

Examiner tips

  • Use the exact wording from the mark scheme – e.g. ‘horizontal row’ for period, ‘vertical column’ for group.
  • Show the link between electron shells and periods, and outer‑shell electrons and groups.
  • Keep the answer concise – 5 points, so one sentence per point.
  • Avoid extra commentary or examples that aren’t asked for.

Common mistakes

  • Confusing ‘period’ with ‘group’ or vice versa.
  • Mentioning only the number of electrons in the outer shell for periods instead of shells.
  • Using vague terms like ‘row’ or ‘column’ without specifying horizontal or vertical.

Mark scheme (5 marks)

  1. A period is a row of the periodic table
  2. Elements in the same period have the same number of electron shells
  3. A group is a column of the periodic table
  4. Elements in the same group have similar chemical properties
  5. Elements in the same group have the same number of electrons in their outer shell

Key terms in this question

period · group

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