What is a polyatomic ion? Consulting p.117 in text, list the formulas and names of at least 10 polyatomic ions. When writing the
overall formula of an ionic compound involving polyatomic ions, why are parentheses used around the formula of a polyatomic ion when more than one such ion is present? Give an example.
Polyatomic ions are ions composed for more than 1 atom. There are polyanions and polycations.
Polyanions have a negative charge and polycations have a positive charge.
Examples
Polyanions Polycations
acetate CH₃COO⁻ ammonium NH₄⁺¹
bromate BrO₃⁻
chlorate ClO₃⁻
hydroxide OH⁻
nitrate NO₃⁻
nitrite NO₂⁻
sulfate SO₄⁻²
phosphate PO₄⁻³
permanganate MnO₄⁻
We write parentheses before or after a polyatomic ion to emphasize that the oxidation number of the atom which interacts with it affects all the atoms that form part of the polyatomic ion.
