1
Write elemental halogens as diatomic molecules in equations: use $Cl_2$ , $Br_2$ and $I_2$ , not $Cl$ , $Br$ or $I$ .
2
Check whether an element is written as single atoms or diatomic molecules before balancing. Chlorine is Cl₂, not Cl.

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GCSE Chemistry · key term

Diatomic molecule

Definition

A molecule containing two atoms, such as O₂ or Cl₂.

Used by AQA and OCR

Specification 4.1.2.6 · Paper 1

A molecule containing two atoms joined by a covalent bond.
Revise: Physical Properties and Halide Formation

Specification C3.1c · Paper 1 (Foundation), Paper 3 (Higher)

Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)

1
Write elemental halogens as diatomic molecules in equations: use $Cl_2$ , $Br_2$ and $I_2$ , not $Cl$ , $Br$ or $I$ .
2
Check whether an element is written as single atoms or diatomic molecules before balancing. Chlorine is Cl₂, not Cl.

Create a free account to read GCSE Chemistry revision notes for your exam board and track your progress.