The Group 7 Halogens — Group 7: The Halogens | IGCSE Chemistry

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 6% of your exam marks.

stable

Low

Stable6%

Displacement reactions and physical property trends tested consistently.

Group 7 contains the halogens: fluorine, chlorine, bromine, iodine and astatine
They are reactive non-metals, all toxic, and many are coloured
Each halogen atom has seven electrons in its outermost shell, which gives the group its family resemblance
Halogens exist as diatomic molecules (F₂, Cl₂, Br₂, I₂) — a pair of atoms held together by one single covalent bond, sharing a pair of electrons

Halogen	State at room temperature	Colour	Note
Fluorine, F₂	Gas	Pale yellow	Most reactive of all elements
Chlorine, Cl₂	Gas	Pale yellow-green	Dense, pungent
Bromine, Br₂	Liquid	Red-brown	Volatile; gives orange-brown vapour
Iodine, I₂	Solid	Dark grey, shiny crystals	Sublimes on warming to a violet vapour

The colour deepens as you go down the group (pale yellow → yellow-green → red-brown → dark grey/violet)

Both the melting point and the boiling point increase steadily down the group
F₂ boils at −188 °C, Cl₂ at −34 °C, Br₂ at 59 °C, I₂ at 184 °C
The halogens are simple molecular structures, so it is the intermolecular forces between molecules that are broken on melting or boiling — not the strong covalent bond inside each molecule
As the molecules get larger going down the group, the intermolecular forces become stronger and more energy is needed to overcome them — so the melting and boiling points rise