1. Chapter 6 Ionic and Molecular Compounds
6.4 Polyatomic Ions
Learning Goal Write the name and formula for an ionic compound containing a polyatomic ion.

2. Polyatomic Ions
A polyatomic ion is a group of atoms with an overall ionic charge. NH4+ ammonium OH− hydroxide NO3− nitrate NO2− nitrite CO32− carbonate PO43− phosphate HCO3− hydrogen carbonate (or bicarbonate)

3. Polyatomic Ions
Figure 6.3 Many products contain polyatomic ions, which are groups of atoms that have an ionic charge.

4. Naming Polyatomic Ions
The names of the common polyatomic anions
end in ate
NO3− nitrate PO43− phosphate
with one oxygen less end in ite
NO2− nitrite PO33− phosphite
with hydrogen use prefix hydrogen (or bi)
HCO3− hydrogen carbonate (bicarbonate)
HSO3− hydrogen sulfite (bisulfite)

5. Names and Formulas of Common Polyatomic Ions

6. Names and Formulas of Common Polyatomic Ions

7. Writing Formulas for Compounds with Polyatomic Ions
To write the correct formula for compounds containing polyatomic ions, first determine the ratio of ions using charge balance. Write the formula for calcium nitrate. 1. The total negative and positive charges must equal zero

8. Writing Formulas for Compounds with Polyatomic Ions
2. When more than one polyatomic ion is needed for charge balance, the subscript is written outside the closing parenthesis of the polyatomic ion.
Ca NO3−  Ca(NO3)2
Calcium ion Nitrate ions Calcium nitrate

9. Guide to Writing Formulas with Polyatomic Ions

10. Learning Check
Write the formula for aluminum bicarbonate.

11. Solution
Write the formula for aluminum bicarbonate. Step 1 Identify the cation and polyatomic ion (anion). Cation Polyatomic Ion (anion) Al3+ HCO3−

12. Solution
Write the formula for aluminum bicarbonate. Step 2 Balance the charges.

13. Solution
Write the formula for aluminum bicarbonate. Step 3 Write the formula, cation first, using the subscripts from the charge balance. Al HCO3−  Al(HCO3)3 Aluminum + 3 Bicarbonate ions Aluminum bicarbonate

14. Naming Ionic Compounds with Polyatomic Ions
When naming ionic compounds containing polyatomic ions,
write the name of the positive ion, usually a metal first
write the name of the polyatomic ion last
Learn to recognize polyatomic ions in ionic compound names and formulas.

15. Naming Ionic Compounds with Polyatomic Ions

16. Guide to Naming Ionic Compounds with Polyatomic Ions

17. Learning Check
Name the following ionic compounds: A. KClO3 B. Mn(OH)2

18. Solution
Name the following ionic compounds: A. KClO3 B. Mn(OH)2

19. Summary of Naming Ionic Compounds

20. Learning Check
Name the following ionic compounds. A. Na3P B. CuSO4 C. Cr(ClO)3

21. Solution
Name the following ionic compounds. A. Na3P B. CuSO4 C. Cr(ClO)3