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GCSE Combined Science · key term
A small number written at the lower right of a chemical symbol or bracket, showing how many of the preceding atom or group are present in the formula.
Used by AQA and Edexcel
Specification 5.1.1.1, 5.3.1.1 · Paper 3
A small number written below and to the right of a symbol or bracket in a formula, showing how many atoms or groups are present.
Revise: Representing Chemical Reactions and Balancing EquationsIf there is no subscript, the number is one. Brackets allow a whole group to be repeated.
Specification Formulae, equations and hazards · Paper 3, Paper 4
A small number written at the lower right of a chemical symbol or bracket, showing how many of the preceding atom or group are present.
Revise: Chemical formulae and equationsThe small lower number is a subscript; when there is no subscript, the number is one.
Balance equations by changing coefficients, never the subscripts within a chemical formula.
Balance equations by changing coefficients in front of formulae, never by changing subscripts: changing a formula changes the substance.
Write the correct formulae before balancing. Change only the coefficients in front of formulae, never the subscripts within them.
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