Chapter 6 Lecture
Basic Chemistry
Fourth Edition
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.
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Polyatomic Ions
A polyatomic ion is a group of atoms with an
overall ionic charge.
NH4+
ammonium
OH− hydroxide
NO3−
nitrate
NO2−
CO32−
HCO3−
carbonate
PO43− phosphate
hydrogen carbonate (or bicarbonate)
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nitrite
Polyatomic Ions
Figure 6.3 Many products contain polyatomic
ions, which are groups of atoms that have an
ionic charge.
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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)
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Names and Formulas of Common
Polyatomic Ions
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Names and Formulas of Common
Polyatomic Ions
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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
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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.
Ca2+ +
2 NO3−
Calcium ion + 2 Nitrate ions
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
Ca(NO3)2
Calcium nitrate
Guide to Writing Formulas with
Polyatomic Ions
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Learning Check
Write the formula for aluminum bicarbonate.
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Solution
Write the formula for aluminum bicarbonate.
Step 1
Identify the cation and polyatomic
ion (anion).
Cation
Polyatomic Ion (anion)
Al3+
HCO3−
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Solution
Write the formula for aluminum bicarbonate.
Step 2 Balance the charges.
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Solution
Write the formula for aluminum bicarbonate.
Step 3
Write the formula, cation first,
using the subscripts from the charge
balance.
Al3+ +
3 HCO3−  Al(HCO3)3
Aluminum
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+ 3 Bicarbonate ions
Aluminum bicarbonate
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.
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Naming Ionic Compounds with
Polyatomic Ions
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Guide to Naming Ionic Compounds with
Polyatomic Ions
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Learning Check
Name the following ionic compounds:
A. KClO3
B. Mn(OH)2
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Solution
Name the following ionic compounds:
A. KClO3
B. Mn(OH)2
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Summary of Naming Ionic Compounds
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Learning Check
Name the following ionic compounds.
A. Na3P
B. CuSO4
C. Cr(ClO)3
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Solution
Name the following ionic compounds.
A. Na3P
B. CuSO4
C. Cr(ClO)3
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