Question

How can I name compounds containing polyatomic ions?

Answer 1

Basically, you name the ions in the order they occur in the formula. The positive ion is always first, and the negative ion is always second. This is true whether the positive ion is monatomic or polyatomic, or the negative ion is monatomic or polyatomic, or both the ions are. The following URL lists common polyatomic ions, with names, formulas, and charges. http://www2.pvc.maricopa.edu/tutor/chem/chem130/nomenclature/polyatomicion.html

Examples of ionic compounds containing polyatomic ions.

Ionic compounds of the Group 1, 2, and 13 metals containing the negative polyatomic nitrate ion, `"NO"_3^-"`.

`"NaNO"_3"` is named sodium nitrate.
`"Sr(NO"_3)_2"` is named strontium nitrate.
`"Al(NO"_3)_3"` is named aluminum nitrate.

Ionic compounds of the group 1, 2, and 13 metals containing the negative polyatomic sulfate ion, `"SO"_4^(2-)`.

`"Na"_2"SO"_4"` is named sodium sulfate.
`"SrSO"_4"` is named strontium sulfate.
`"Al"_2("SO"_4)_3"` is named aluminum sulfate.

Ionic compounds containing the positive polyatomic ammonium ion, `"NH"_4^+"`.

`"NH"_4"Cl"` is named ammonium chloride.
`"(NH"_4)_3"N"` is named ammonium nitride.

Ionic compounds containing both a positive polyatomic ion and a negative polyatomic ion.

Ammonium ion plus hydroxide ion, `"OH"^-"`
`"NH"_4"OH"` is named ammonium hydroxide.

Ammonium ion plus phosphate ion, `"PO"_4^(3-)"`
`"(NH"_4)_3"PO"_4"` is named ammonium phosphate.

Ionic compounds containing transition metal ions with variable charges and negative polyatomic ions:

Copper can form two ions, copper I, `"Cu"^+"`, and copper II, `"Cu"^(2+)`

Combined with the sulfate ion:
`"Cu"_2"SO"_4` is named copper I sulfate.
`"CuSO"_4"` is named copper II sulfate.

Cobalt can form two ions, cobalt II, `"Co"^(2+)` and cobalt III, `"CO"^(3+)`.

Combined with the hydroxide ion:
`"Co(OH)"_2"` is named cobalt II hydroxide.
`"Co(OH)"_3"` is named cobalt III hydroxide.