Polyatomic ions

Polyatomic ions are ions that are formed from the combination of multiple atoms. When a polyatomic ion forms, the whole group of atoms act as a unit, including the charge e.g. Sulphate = SO4-2

It contains one sulphur atom and four oxygen atoms all bound together as one entire unit. The whole unit carries a charge of -2.

Nitrate = NO4-

Contains one nitrogen atom and three oxygen atoms. The whole unit has a charge of -1.

*Most polyatomic ions carry a negative charge.

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Writing chemical formulas, the charges of the ions must be equal. Compounds are always neutral.

E.g. Sodium(s) + Hydroxide(l) react Sodium Hydroxide.

Na+ + OH- --> NaOH