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.
📖 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.
Practice questions for Group 7: Halogens
How many electrons do halogens have in their outer shell?
Explain why chlorine is more reactive than bromine.