How do group trends in the IGCSE periodic table affect reactivity?
Talimat Academic Team
Education Specialist · 25 May 2026
Group trends in the Cambridge IGCSE periodic table control reactivity by changing how easily atoms lose or gain outer electrons.
For Group 1 alkali metals, reactivity increases down the group. Each element lower in the group has its outer electron in a shell further from the nucleus. The pull on that electron is weaker, so it is lost more readily in a reaction.
Group 7 halogens work the opposite way. Fluorine at the top is the most reactive halogen; iodine at the bottom is the least. Halogens react by gaining an electron, and a smaller atom does this far more effectively than a larger one.
A common exam mistake in Cambridge IGCSE Chemistry is applying Group 1 logic to Group 7 without reversing it. The key question to ask is always: is this element losing or gaining an electron?
Group position also sets an element's valency. These six examples cover the patterns tested most often in online tutoring sessions and on past papers:
- Group 1: valency of 1 (e.g. sodium)
- Group 2: valency of 2 (e.g. magnesium)
- Group 7: valency of 1 (e.g. chlorine)
- Group 6: valency of 2 (e.g. oxygen)
- Group 0: valency of 0 (unreactive)
Transition metals are the exception. They carry variable valency, so the exam will usually state the charge directly.
Displacement reactions are a classic test of group trend knowledge. A more reactive halogen displaces a less reactive one from its salt solution. Chlorine displaces bromide and iodide; bromine displaces iodide but not chloride.
Moving across a period rather than down a group, atomic radius decreases as more protons pull the outer electrons closer to the nucleus. Elements also shift from metals on the left to non-metals on the right within the same period.
For a full breakdown of period trends, electron configurations, and common exam question formats, see our blog. If you want structured practice with real mark schemes from CAIE, Edexcel, or AQA, contact us and we will match you with a specialist science tutor in under ten minutes.