This definitions covers Key Definitions within Group 7: Halogens for GCSE Chemistry. Revise Group 7: Halogens in Atomic Structure for GCSE Chemistry with 22 exam-style questions and 21 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 7 of 12 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
Topic position
Section 7 of 12
Practice
22 questions
Recall
21 flashcards
📖 Key Definitions
Halogens: The elements in Group 7 of the periodic table (F, Cl, Br, I, At) — reactive non-metals with 7 outer electrons that form −1 ions (halide ions) by gaining one electron.
Diatomic molecule: A molecule made of two atoms of the same element bonded together, e.g., Cl₂, Br₂, I₂. All halogens exist as diatomic molecules.
Halide ion: A negatively charged ion formed when a halogen gains one electron, e.g., Cl⁻ (chloride), Br⁻ (bromide), I⁻ (iodide).
Displacement reaction: A reaction where a more reactive element displaces a less reactive element from a compound. A more reactive halogen displaces a less reactive halide ion.
Reactivity trend (Group 7): Reactivity decreases going down Group 7 because the outer shell is further from the nucleus, making it harder to attract and gain an additional electron.
Keep building this topic
Read this section alongside the surrounding pages in Group 7: Halogens. That gives you the full topic sequence instead of a single isolated revision point.
Practice Questions for Group 7: Halogens
How many electrons do halogens have in their outer shell?
Explain why chlorine is more reactive than bromine.
Quick Recall Flashcards
22 questions on Group 7: Halogens — practise free
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