Question: do parentheses appear in the formulas of ionic compounds?
Answer: When writing the chemical formula of a compound that contains a polyatomic ion, in order to indicate more than one polyatomic ion in the formula, put parentheses around the polyatomic ion before writing the subscript. ... There is an extra bracket around the 'SO4' unit. (NH4)2(SO4)1. Subscript of '1' is usually not written ...