Question

Are polyatomic ions molecular compounds or ionic compounds?

Answer 1

Polyatomic ions are ions.

However, the atoms in polyatomic ions are held together by covalent bonds.

Compounds containing polyatomic ions are ionic compounds.

The basic rule of thumb is ionic compounds take place between a positive ionic metal and a negative ionic non-metal. An ion from left of the metalloid staircase and an ion from right of the metalloid staircase.

A molecular compound is a molecule formed between two non-metals from right of the metalloid staircase. Each non metal completes the octet rule by sharing valence electrons.

Examples of polyatomic ions include `SO_4^(2-)` (sulfate), `CO_3^(2-)` (carbonate), `PO_4^(3-)` (phosphate), `OH^(-)` (hydroxide) and `NH_4^(+)` (ammonium).

In the last two examples the hydrogen takes on the properties of a halogen and shares its one electron.

Examples of compounds that contain polyatomic ions are `(NH_4)_2SO_4`, `Al_2(CO_3)_2`,`Fe_3(PO_4)_2`, and `Ba(OH)_2`.