1. tightly bonded group of atoms with a + or – charge overall
Section 4: Polyatomic Ions O H N H N O O H H
polyatomic ion:
tightly bonded group of atoms with a + or – charge overall O O O P S O O O O O

2. Common Polyatomic Ions
Name
Formula
Charge
ammonium
NH4+ +1
hydroxide
OH– -1
acetate
C2H3O2–
nitrate
NO3–
nitrite
NO2–
bicarbonate
HCO3–
carbonate
CO32– -2
sulfate
SO42–
sulfite
SO32–
phosphate
PO43– -3
handout list of polyatomics

3. Names and Formulas for Compounds with Polyatomic Ions
Same rules as with all compounds.
Example: calcium nitrate
symbols of ions with
charges (as superscripts)
crisscross (to get subscripts)
erase charges
use ( ) for multiple
polyatomic ions
Ca2+ NO3–
Ca2+ NO3–
CaNO32 ?
Ca(NO3)2

4. (use your polyatomic ions sheet)
Write the formulas for the following compounds with polyatomic ions.
(use your polyatomic ions sheet)
ammonium nitrate
calcium phosphate
iron(III) carbonate
NH4+ NO3–
NH4NO3
Ca2+ PO43–
Ca3(PO4)2
Fe3+ CO32–
Fe2(CO3)3

5. 1. Which of the following are positively charged polyatomic ions?
Quick Quiz!
1. Which of the following are positively charged polyatomic ions?
1) ammonium ion
2) nitrate ion
3) iron(III) ion
1 only
2 only
1 and 2
1 and 3
NH4+
NO3–
Fe3+

6. 2. What is the correct name for Mg(OH)2 ? magnesium oxide
Quick Quiz.
2. What is the correct name for Mg(OH)2 ?
magnesium oxide
magnesium hydroxide
magnesium(II) hydroxide
magnesium(II) hydroxate

7. Cu+ SO42– 3. What is the correct formula for copper(I) sulfate? CuS
Quick Quiz.
3. What is the correct formula for
copper(I) sulfate?
CuS
CuSO4
Cu2SO4
Cu(SO4)2
Cu+ SO42–

8. 4. Which one of the following formulas is named correctly?
Quick Quiz.
4. Which one of the following formulas is named correctly?
sodium bicarbonate, Na2CO3
potassium nitrate, KNO2
sodium acetate, NaC2H3O2
lithium sulfide, Li2SO4