# Iodine is a halogen in Group 7 of the periodic table. When iodine reacts with potassium metal, potassium iodide is formed. Explain why iodine is a less reactive halogen than chlorine, and state the type of ion formed when iodine reacts with potassium.

> Pearson Edexcel International GCSE Chemistry (4CH1) — 2.2 Group 7 (halogens) · Explain · 4 marks

> Halogens react with metals to form ionic compounds called metal halides. The reactivity of halogens decreases down Group 7.

## Mark scheme (4 marks)

1. Iodine atoms are larger than chlorine atoms / iodine has more electron shells than chlorine
2. The outer shell / incoming electron is further from the nucleus in iodine, so the nucleus attracts an incoming electron less strongly
3. Therefore iodine gains an electron less easily / less readily than chlorine, making it less reactive
4. Iodine forms an iodide ion / I⁻ ion with a 1− charge

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