1. Polyatomic Ions O N O O O O O P S O O O O O N H H polyatomic ion:
You know how single atoms can ionically bond with other atoms as… ions? Well, a group of atoms can act as a cation or an anion (almost always) , as well. Individually, these groups of atoms are known as a:
polyatomic ion:
a tightly (covalently) bonded group of atoms with a + or– charge (almost always) , overall N H N O O H H O O O P S O O O O O

2. Common Polyatomic Ions (yes, write all of this down)
Name
Formula
Charge
ammonium
NH4+ 1+
hydroxide
OH– 1–
acetate
C2H3O2–
permanganate
MnO4–
nitrate
NO3–
chlorate
ClO3–
hydrogencarbonate
(bicarbonate is what everyone actually calls it, you need to know this)
HCO3–
carbonate
CO32– 2–
sulfate
SO42–
phosphate
PO43– 3–
handout list of polyatomics

3. many end in –ate Monatomic Polyatomic nitride nitrate N3– NO3–
the anions all end in –ide
many end in –ate
Note: remember, though, all monatomic cations have the same name as the atom
Monatomic
Polyatomic
nitride
nitrate
N3–
NO3–
ammonium
NH4+
chloride
chlorate
Cl–
ClO3–
hydroxide
OH–
Interestingly, most polyatomic ions, that we care about, have oxygens in their formulas (probably has something to do with the part of the atmosphere we care about)
sulfide
sulfate
S2–
SO42–
phosphide
phosphate
P3–
PO43–

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

5. (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

6. 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+

7. 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

8. 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–

9. 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