You are watching: Locate the polyatomic ion in the compound mgso4
Some ions consist of groups of atoms bonded together and have an overall electric charge. Because these ions contain more than one atom, they are called polyatomic ions. Polyatomic ions have characteristic formulas, names, and charges that should be memorized. For example, NO3− is the nitrate ion; it has one nitrogen atom and three oxygen atoms and an overall 1− charge. Table (PageIndex1) lists the most common polyatomic ions.
|acetate ion||C2H3O2− (also written CH3CO2−)|
|hydrogen carbonate ion (bicarbonate ion)||HCO3−|
|hydrogen phosphate ion||HPO42−|
|dihydrogen phosphate ion||H2PO4−|
|hydrogen sulfate ion (bisulfate ion)||HSO4−|
The rule for constructing formulas for ionic compounds containing polyatomic ions is the same as for formulas containing monatomic (single-atom) 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. This is to show that the subscript applies to the entire polyatomic ion. An example is Ba(NO3)2.
Writing Formulas for Ionic Compounds Containing Polyatomic Ions
Writing a formula for ionic compounds containing polyatomic ions also involves the same steps as for a binary ionic compound. Write the symbol and charge of the cation followed by the symbol and charge of the anion.
Example (PageIndex1): Calcium Nitrate
Write the formula for calcium nitrate.
|1. Write the symbol and charge of the cation (metal) first and the anion (nonmetal) second.||(ceCa^2+ : : : : : ceNO_3^-)|
|2. Transpose only the number of the positive charge to become the subscript of the anion and the number only of the negative charge to become the subscript of the cation.|
Example (PageIndex3): Naming Ionic Compounds
Write the proper name for each ionic compound.(NH4)2S AlPO4, Fe3(PO4)2