1. Common Polyatomic Ions (Memorize!)
Name
Hg22+
mercury (I)
NH4+
ammonium
NO3-
nitrate
C2H3O2-
acetate
OH-
hydroxide
CN-
cyanide
ClO3-
chlorate
MnO4-
permanganate
NCS-
thiocyanate
BrO3-
bromate
Ion
Name
CO32-
carbonate
SO42-
sulfate
Cr2O72-
dichromate
CrO42-
chromate
O22-
peroxide
C2O42-
oxalate
PO43-
phosphate

2. Common Polyatomic Ions (Must Know All of These
Common Polyatomic Ions (Must Know All of These! Use Naming Patterns to Help!)
Ion
Name
Hg22+
mercury (I)
NH4+
ammonium
NO2-
nitrite
NO3-
nitrate
SO32-
sulfite
SO42-
sulfate
HSO4-
hydrogen sulfate
(bisulfate)
OH-
hydroxide
CN-
cyanide
PO43-
phosphate
HPO42-
hydrogen phosphate
H2PO4-
dihydrogen phosphate
Ion
Name
NCS-
thiocyanate
CO32-
carbonate
HCO3-
Hydrogen carbonate
(bicarbonate)
ClO-
hypochlorite
ClO2-
chlorite
ClO3-
chlorate
ClO4-
perchlorate
C2H3O2-
acetate
MnO4-
permanganate
Cr2O72-
dichromate
CrO42-
chromate
O22-
peroxide
C2O42-
oxalate

3. Common Polyatomic Ions
Name
Hg22+
mercury (I)
NH4+
ammonium
NO2-
nitrite
NO3-
nitrate
SO32-
sulfite
SO42-
sulfate
HSO4-
hydrogen sulfate
(bisulfate)
OH-
hydroxide
CN-
cyanide
PO43-
phosphate
HPO42-
hydrogen phosphate
H2PO4-
dihydrogen phosphate
Ion
Name
NCS-
thiocyanate
CO32-
carbonate
HCO3-
Hydrogen carbonate
(bicarbonate)
ClO-
hypochlorite
ClO2-
chlorite
ClO3-
chlorate
ClO4-
perchlorate
C2H3O2-
acetate
MnO4-
permanganate
Cr2O72-
dichromate
CrO42-
chromate
O22-
peroxide
C2O42-
oxalate

4. Common Polyatomic Ions
Name
Hg22+
mercury (I)
NH4+
ammonium
NO2-
nitrite
NO3-
nitrate
SO32-
sulfite
SO42-
sulfate
HSO4-
hydrogen sulfate
(bisulfate)
OH-
hydroxide
CN-
cyanide
PO43-
phosphate
HPO42-
hydrogen phosphate
H2PO4-
dihydrogen phosphate
Ion
Name
NCS-
thiocyanate
CO32-
carbonate
HCO3-
Hydrogen carbonate
(bicarbonate)
ClO-
hypochlorite
ClO2-
chlorite
ClO3-
chlorate
ClO4-
perchlorate
C2H3O2-
acetate
MnO4-
permanganate
Cr2O72-
dichromate
CrO42-
chromate
O22-
peroxide
C2O42-
oxalate

5. Common Polyatomic Ions
Name
Hg22+
mercury (I)
NH4+
ammonium
NO2-
nitrite
NO3-
nitrate
SO32-
sulfite
SO42-
sulfate
HSO4-
hydrogen sulfate
(bisulfate)
OH-
hydroxide
CN-
cyanide
PO43-
phosphate
HPO42-
hydrogen phosphate
H2PO4-
dihydrogen phosphate
Ion
Name
NCS-
thiocyanate
CO32-
carbonate
HCO3-
Hydrogen carbonate
(bicarbonate)
ClO-
hypochlorite
ClO2-
chlorite
ClO3-
chlorate
ClO4-
perchlorate
C2H3O2-
acetate
MnO4-
permanganate
Cr2O72-
dichromate
CrO42-
chromate
O22-
peroxide
C2O42-
oxalate

6. Naming Patterns To Know Polyatomic Ions:
Anion ending:
one more oxygen than “-ate” = per-___-ate
–ate
one less oxygen than “-ate” = –ite
two less oxygen than “-ate” = hypo-___-ite
Hydrogen bonded:
If hydrogen is bonded to the polyatomic ion, then start the name with “hydrogen” (more than one, “dihydrogen”, etc.)
Examples
Hydrogen carbonate = HCO3-
Hypochlorite = ClO-
Chlorite = ClO2-
Perchlorate = ClO4-
Nitrite = NO2-
Sulfite = SO32-
Hydrogen sulfate = HSO4-
Hydrogen phosphate = HPO42-
Dihydrogen phosphate = H2PO4-