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The following are lists of polyatomic ions. These may be helpful when completing ChemSkill Builder and Homework problems. The exams will include only the nine we have focused on:


The 9 polyatomic ions to know and write on your notecard:
Name Charge Formula
Hydroxide 1- OH-
Cyanide 1- CN-
Nitprice 1- NO3-
Acetate 1- CH3COO-
Carbonate 2- CO32-
Phospdislike 3- PO43-
Hydronium 1+ H3O+
Ammonium 1+ NH4+
Sulfate 2- SO42-

Other polyatomic ions:

acetateC2H3O21-
ammoniumNH41+
arsenateAsO43-
azideN31-
bicarbonate (hydrogen carbonate)HCO31-
bisulfate (hydrogen sulfate)HSO41-
borateBO33-
bromateBrO31-
carbonateCO32-
chlorateClO31-
chromateCrO42-
cyanateOCN1-
cyanideCN1-
dichromateCr2O72-
dihydrogen phosphateH2PO41-
ferricyanideFe(CN)63-
ferrocyanideFe(CN)64-
formateCHO21-
hydrogen carbonate (bicarbonate)HCO31-
hydrogen sulfate(bisulfate)HSO41-
hydroxideOH1-
iodateIO31-
manganate**MnO42-
metasilicateSiO32-
molybdateMoO42-
monohydrogen phosphateHPO42-
nitrateNO31-
oxalateC2O42-
permanganate**MnO41-
phosphatePO43-
phthalateC8H4O42-
selenateSeO42-
silicateSiO44-
sulfateSO42-
tartrateC4H4O62-
thiocyanateSCN1-
thiosulfateS2O32-
tungstateWO42-

** Exception to prefix rulesNOTE: -ite ending means one less oxygen than the -ate form. PREFIXES: per- = one more oxygen than -ate hypo- = one less oxygen than -ite

Ions arranged by family

Polyatomic cations other than ammonium, hydronium, and mercury(I) aren"t usually encountered in general chemistry. Most common polyatomic anions occur in "families". All members of the family share the same central element and the same charge. There are three common types of variations within the family:

Different members of the family can have numbers of oxygens. Each member of the family can combine with hydrogen ions to partially neutralize their negative charge. Some members of the family can have sulfur substituted for oxygen. Other variations exist but are less common.

Table of common polyatomic cations, arranged by family.

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Alternate names are given in italics. Select the name of the ion for information about its occurrence, uses, properties, and structure. Blank entries are uncommon or unstable; for a complete table see the Field Guide to Polyatomic Ions.

carbon
nitrogensulfurchlorine
CO32-carbonate
HCO3-hydrogen carbonate(bicarbonate)
NO3-nitrate
NO2-nitrite
SO42-sulfate
SO32-sulfite
S2O32-thiosulfate
HSO4-hydrogen sulfate(bisulfate)
HSO3-hydrogen sulfite(bisulfite)
ClO4-
perchlorate
ClO3-chlorate
ClO2-chlorite
ClO-hypochlorite
phosphoruscyanidecationsmetal oxyanions
PO43-phosphate
HPO42-hydrogen phosphate
H2PO4-dihydrogen phosphate
CN-
cyanide
OCN-cyanate
SCN-thiocyanate
NH4+
ammonium
H3O+hydronium
Hg22+mercury(I)
CrO42-
chromate
Cr2O72-dichromate
MnO4-permanganate
oxygenorganics
OH-hydroxide
O22-peroxide
C2H3O2-
acetate

Common naming practices

If you can remember the formula of the ion whose name ends with ate, you canusually work out the formulas of the other family members as follows: modify stem name with:
meaningexamples
-atea common form, containing oxygen chlorate, ClO3-nitrate, NO3-sulfate, SO42-
-iteone less oxygen than -ate formchlorite, ClO2-sulfite, SO32-nitrite, NO2-
per-, -atesame charge, but contains one more oxygen than -ate formperchlorate, ClO4-perbromate, BrO4-
hypo-, -itesame charge, but contains one less oxygen than the -ite formhypochlorite, ClO-hypobromite, BrO-
thio-replace an O with an Sthiosulfate, S2O32-thiosulfite, S2O22-
Some anions can capture hydrogen ions. For example, carbonate (CO32- can capture an H+ to produce hydrogen carbonate HCO3- (often called bicarbonate). Each captured hydrogen neutralizes one minus charge on the anion.
modify stem name with:meaningexamples
hydrogenor bi-(1) captured H+ ionshydrogen carbonate, HCO3- (a.k.a. bicarbonate)hydrogen sulfate, HSO4- (a.k.a. bisulfate)
dihydrogen(2) captured H+ ionsdihydrogen phosphate, H2PO4-

Table of common polyatomic cations, arranged by charge. Alternate names are given in italics. Select the name of the ion for information about its occurrence, uses, properties, and structure.

+2
Hg22+mercury(I) or mercurous
+1
NH4+ammonium
H3O+hydronium
-1
C2H3O2-acetate
ClO3-chlorate
ClO2-chlorite
CN-cyanide
H2PO4-dihydrogen phosphate
HCO3-hydrogen carbonate or bicarbonate
HSO4-hydrogen sulfate or bisulfate
OH-hydroxide
ClO-hypochlorite
NO3-nitrate
NO2-nitrite
ClO4-perchlorate
MnO4-permanganate
SCN-thiocyanate
-2
CO32-carbonate
CrO42-chromate
Cr2O72-dichromate
HPO42-hydrogen phosphate
O22-peroxide
SO42-sulfate
SO32-sulfite
S2O32-thiosulfate
-3
PO43-phosphate

Ion

Two-Dimensional Structure

Three-Dimensional Representation

Ammonium NH4+

*
*
Hydronium H3O+
*
*

Ion

Two-Dimensional Structure

Three-Dimensional Representation

Bicarbonate HCO3-
*
*
Cyanide CN-
*
*
Hydrogen Sulfate HSO4-
*
*
Hydroxide OH-
*
*
Nitrate NO3-
*
*
Nitrite NO2-
*
*
Perchlorate ClO4-
*
*
Permanganate MnO4-
*
*

Ion

Two-Dimensional Structure

Three-Dimensional Representation

Carbonate CO32-
*
*
Chromate CrO42-
*
*
Dichromate Cr2O72-
*
*
Hydrogen Phosphate HPO42-
*
*
Sulfate SO42-
*
*
Sulfite SO32-
*
*
Thiosulfate S2O32-
*
*

Ion

Two-Dimensional Structure

Three-Dimensional Representation

Phosphate PO43-
*
*
Polyatomic Formulas - Polyatomic ions are made from more that one atom. This group of atoms act together as one unit with a single charge. Each of the polyatomic ions have a unique name.

Table of Polyatomic Ions

1+1-2-3-
ammonium , NH4 +acetate, C2H302-carbonate, CO32-phosphate, PO43-
bicarbonate, HCO3 -chromate,CrO42-
bisulfate, HSO4 -dichromate,Cr2O72-
bisulfite, HSO3 -oxalate,C2O42-
chlorate,ClO3-peroxide,022-
chlorite,ClO2-silicate,SiO32-
cyanide,CN-sulfate,SO42-
hydroxide,OH-sulfite,SO32-
hypochlorite,ClO-tartrate,C4H4062-
iodate,IO3-thiosulfate,S2O32-
nitrate,NO3-
nitrite,NO2-
perchlorate,ClO4-
permanganate,MnO4-

Most of the polyatomic ions are anions. The formula for the compound will contain both a cation and an anion to balance the overall charge of the compound.

See more: The Word From The Passage That Best Defines The Topic Is, Ode On A Grecian Urn

The cation is named normally and the anion is given the name of the actual anion. An easy way to recognize these formulas is the fact that they are made up of more that two elements and, usually, the first element is a metal.