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GCSE Chemistry · key term
An ion made from more than one covalently bonded atom, such as nitrate, , or sulfate, .
Used by AQA, Edexcel and OCR
Specification 4.4.2.2 · Paper 1
Revise: Neutralisation and SaltsNitrate and sulfate are polyatomic ions: each group acts as one ion. If more than one whole polyatomic ion is required, put its formula in brackets before adding the subscript.
Specification 0.1, 1.22, 1.25, 1.26 · Paper 1, Paper 2
An ion made from more than one atom, such as NH₄⁺, OH⁻ or SO₄²⁻.
Revise: Formulae of Elements and IonsNitrate, carbonate and sulfate are oxygen-containing polyatomic ions whose names end in -ate. Hydroxide, OH⁻, is an important name to learn separately rather than trying to infer it from that pattern.
An ion made from two or more atoms joined together and carrying an overall charge.
A charged group of two or more covalently bonded atoms that behaves as one ion, such as the nitrate ion.
An ion formed from two or more chemically joined atoms that act as a single charged unit, such as or .
Specification C3.1d · Paper 1 (Foundation), Paper 3 (Higher)
An ion containing more than one covalently bonded atom, such as hydroxide, , or sulfate, .
Revise: Deducing Compound FormulaeTreat a polyatomic ion as one complete unit. If more than one of that ion is required, place its formula in brackets and write the number outside.
Keep a polyatomic ion such as or together. Use brackets when more than one whole ion is needed, as in .
Use brackets when more than one polyatomic ion is needed, as in and .
Never change a subscript within a polyatomic ion: sulfate remains and nitrate remains .
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