Misconception 1: "All halogens are gases at room temperature"
Only fluorine and chlorine are gases at room temperature. Bromine is a liquid (one of only two elements that are liquid at room temperature — the other is mercury). Iodine is a solid. This trend (gas → liquid → solid going down the group) reflects increasing intermolecular forces as molecular size increases. Examiners regularly test this knowledge.
Misconception 2: "Halogens react by losing electrons, like alkali metals"
Halogens are non-metals and react by GAINING one electron to achieve a full outer shell, forming negative halide ions (Cl⁻, Br⁻, I⁻). Alkali metals react by LOSING one electron to form positive ions. This is the key contrast between the groups — one gains, one loses.
Misconception 3: "Reactivity increases going down Group 7 (same as Group 1)"
Reactivity DECREASES going down Group 7. This is the opposite of Group 1. In Group 7, atoms need to gain an electron — smaller atoms do this more easily because the outer shell is closer to the nucleus (stronger attraction). In Group 1, atoms need to lose an electron — larger atoms do this more easily because the outer electron is further away (weaker hold).
This common misconceptions covers Common Misconceptions 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 8 of 12 in this topic. Use this common misconceptions to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Group 7: Halogens
How many electrons do halogens have in their outer shell?
Explain why chlorine is more reactive than bromine.