Final answer:
When there is more than one polyatomic ion present in a compound, the formula of the ion is placed in parentheses with a subscript outside of the parentheses indicating how many of those ions are in the compound. To count the total number of atoms in a formula with polyatomic ions enclosed in parentheses, use the subscript outside the parentheses as a multiplier for each atom or number of atoms.
Step-by-step explanation:
When there is more than one polyatomic ion present in a compound, the formula of the ion is placed in parentheses with a subscript outside of the parentheses indicating how many of those ions are in the compound. For example, in the compound Ba(NO3)2, there are two nitrate ions present.
To count the total number of atoms in a formula with polyatomic ions enclosed in parentheses, use the subscript outside the parentheses as a multiplier for each atom or number of atoms. This ensures that you account for all the atoms in the compound. It is important to remember that polyatomic ions have characteristic formulas, names, and charges that should be memorized.
The rule for constructing formulas for ionic compounds containing polyatomic ions is the same as for formulas containing monatomic ions: the positive and negative charges must balance. If more than one of a particular polyatomic ion is needed to balance the charge, the entire formula for the polyatomic ion must be enclosed in parentheses and the numerical subscript is placed outside the parentheses to show that it applies to the entire polyatomic ion.