Group 7: The Halogens

This lesson covers the properties, trends and reactions of the Group 7 elements (the halogens), as required by the Edexcel GCSE Combined Science specification (1SC0). You need to know their physical and chemical properties, how reactivity changes down the group, and be able to explain halogen displacement reactions.

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The Group 7 Elements

The halogens are the non-metal elements in Group 7 of the periodic table:

Element	Symbol	Atomic Number	State at Room Temperature	Colour	Electron Configuration
Fluorine	F₂	9	Gas	Pale yellow	2, 7
Chlorine	Cl₂	17	Gas	Yellow-green	2, 8, 7
Bromine	Br₂	35	Liquid	Red-brown	2, 8, 18, 7
Iodine	I₂	53	Solid	Dark grey/purple vapour	2, 8, 18, 18, 7
Astatine	At₂	85	Solid (radioactive, very rare)	—	—

Key Points