Group – IGCSE Chemistry Definition
IGCSE Chemistry definition of group: a vertical column in the periodic table. Covers group number, electron configuration, and exam tips for Cambridge 0620.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
Understanding what a group is — and what the group number tells you about electron configuration — is fundamental to the entire periodic table topic. Questions about groups appear on every paper, from multiple choice to extended writing.
The 0620 definition
A group is a vertical column of elements in the periodic table. Elements in the same group have the same number of electrons in their outer shell and therefore similar chemical properties.
Group number and outer electrons
| Group | Outer electrons | Example element | Electron configuration |
|---|---|---|---|
| I | 1 | Na | 2, 8, 1 |
| II | 2 | Mg | 2, 8, 2 |
| III | 3 | Al | 2, 8, 3 |
| IV | 4 | C | 2, 4 |
| V | 5 | N | 2, 5 |
| VI | 6 | O | 2, 6 |
| VII | 7 | Cl | 2, 8, 7 |
| 0 | Full (2 or 8) | Ne | 2, 8 |
The link is direct: group number = number of outer electrons (except Group 0, where the shell is full).
Why elements in the same group have similar properties
Chemical reactions involve the outer-shell electrons. Since elements in the same group have the same number of outer electrons, they react in similar ways:
- Group I (alkali metals): all lose 1 electron → form +1 ions
- Group VII (halogens): all gain 1 electron → form −1 ions
- Group 0 (noble gases): full outer shell → unreactive
Trends within a group
Going down a group, atoms have more electron shells. This means:
- Atomic radius increases
- Shielding increases
- For metals (Groups I–II): reactivity increases (easier to lose electrons)
- For non-metals (Group VII): reactivity decreases (harder to gain electrons)
Worked exam question
Chlorine and bromine are both in Group VII. (a) State how many electrons are in the outer shell of a chlorine atom. [1] (b) Explain why chlorine and bromine have similar chemical properties. [1]
Mark scheme
(a) 7 [1]
(b) They have the same number of electrons in their outer shell [1]
Common exam mistakes
- Confusing groups (vertical columns) with periods (horizontal rows).
- Saying the group number gives the total number of electrons — it gives the number of outer-shell electrons only.
- Forgetting that Group 0 has a full outer shell rather than zero electrons.
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