GCSE Chemistry · Edexcel 1CH0 · Topic 6B
Group 7
Key points
- Halogens exist as diatomic molecules: chlorine (pale green gas), bromine (red-brown liquid), iodine (dark grey solid giving a purple vapour).
- Melting and boiling points increase down the group; reactivity decreases.
- Test for chlorine: it bleaches damp blue litmus paper (it may turn red first).
- Halogens react with metals to form metal halides and with hydrogen to form hydrogen halides, which dissolve in water to form acidic solutions.
- Displacement: a more reactive halogen displaces a less reactive halide, e.g. chlorine + potassium bromide → potassium chloride + bromine.
- Higher tier: these are redox reactions. Reactivity falls down the group because the outer shell is further from the nucleus, so gaining an electron is harder.
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The Group 7 elements, the halogens, are reactive non-metals that exist as diatomic molecules (F_2, Cl_2, Br_2, I_2). Their reactivity decreases down the group, the opposite of Group 1, and displacement reactions let you see this trend in a…
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