Pearson Edexcel International GCSE Chemistry · specification 4CH1 · Paper 1 | Whole paper: Core content, all four topics · Free · no account needed
2(b) Group 7 (halogens) — chlorine, bromine and iodine (4CH1 specification)
A group whose reactivity falls as you go down, and the displacement reactions that prove the order.
Learn it on Incandio
The 2 Incandio pages that teach this — each explained in full, then proved in marked questions, taught back to an AI pupil and defended in a debate. Completely free.
- Group 1 — the Alkali Metals — Metals soft enough to cut with a knife, which set fire to water — and get worse as you go down.
- Group 7 — the Halogens — A green gas, a brown liquid and a grey solid — and a trend that runs the opposite way to Group 1.
The teaching route this belongs to: Topic 2 · Inorganic chemistry (Chemistry) — the lessons in order, with every gate.
Specification coverage
Topic 2 Inorganic chemistry (b) Group 7 (halogens) — chlorine, bromine and iodine — statements 2.4–2.8
Assessment objectives: AO1, AO2. Suggested learning time: 50 minutes.
Required knowledge
- The appearance and physical state of chlorine, bromine and iodine at room temperature
- The pattern of reactivity down the Group and its explanation
- Displacement reactions of halogens with halide solutions
- The reactions of halogens with metals to form metal halides
Required skills
- Predict whether a displacement reaction will occur
- Write ionic equations for displacement
- Explain the trend using electron gain
How it is examined
- Multiple-choice and short-answer recall
- Application of the content to an unfamiliar context
- Extended open-response, marked on the quality of a connected explanation
Common mistakes
- Applying the Group 1 explanation unchanged. Halogens GAIN an electron, so a larger atom holds an incoming electron less strongly and reactivity falls.
- Predicting a displacement in the wrong direction. A more reactive halogen displaces a less reactive one from its salt.
This page maps the specification. The pages above teach it, and the Chemistry lessons hold the whole course — completely free.