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.

What the halogens are

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

Physical state and appearance at room temperature

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

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

Exam tip

Identifying iodine at room temperature

What comes up: a multiple-choice or short-answer question asks for the colour or state of solid iodine at room temperature.

Write: dark grey (shiny) solid. If asked for its vapour on warming, write violet.

Watch out: the mark scheme explicitly rejects "dark brown solid" and "purple gas" as descriptions of the solid at room temperature — brown and purple are the two most common wrong answers, so be precise.

Trend in melting and boiling points

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 overcome 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