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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^-
Nitrate	1-	NO₃^-
Acetate	1-	CH₃COO^-
Carbonate	2-	CO₃^2-
Phosphate	3-	PO₄^3-
Hydronium	1+	H₃O⁺
Ammonium	1+	NH₄⁺
Sulfate	2-	SO₄^2-

Other polyatomic ions:

acetate	C₂H₃O₂^1-
ammonium	NH₄¹⁺
arsenate	AsO₄^3-
azide	N₃^1-
bicarbonate (hydrogen carbonate)	HCO₃^1-
bisulfate (hydrogen sulfate)	HSO₄^1-
borate	BO₃^3-
bromate	BrO₃^1-
carbonate	CO₃^2-
chlorate	ClO₃^1-
chromate	CrO₄^2-
cyanate	OCN^1-
cyanide	CN^1-
dichromate	Cr₂O₇^2-
dihydrogen phosphate	H2PO4^1-
ferricyanide	Fe(CN)₆^3-
ferrocyanide	Fe(CN)₆^4-
formate	CHO₂^1-
hydrogen carbonate (bicarbonate)	HCO₃^1-
hydrogen sulfate(bisulfate)	HSO₄^1-
hydroxide	OH^1-
iodate	IO₃^1-
manganate**	MnO₄^2-
metasilicate	SiO₃^2-
molybdate	MoO₄^2-
monohydrogen phosphate	HPO₄^2-
nitrate	NO₃^1-
oxalate	C₂O₄^2-
permanganate**	MnO₄^1-
phosphate	PO₄^3-
phthalate	C₈H₄O₄^2-
selenate	SeO₄^2-
silicate	SiO₄^4-
sulfate	SO₄^2-
tartrate	C₄H₄O₆^2-
thiocyanate	SCN^1-
thiosulfate	S₂O₃^2-
tungstate	WO₄^2-

         ** Exception to prefix rules
NOTE: -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. 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

nitrogen

sulfur

chlorine


CO₃^2-	carbonate



HCO₃^-	hydrogen carbonate (bicarbonate)


NO₃^-	nitrate
NO₂^-	nitrite


SO₄^2-	sulfate
SO₃^2-	sulfite

S₂O₃^2-	thiosulfate
HSO₄^-	hydrogen sulfate (bisulfate)
HSO₃^-	hydrogen sulfite (bisulfite)

ClO₄^-	perchlorate
ClO₃^-	chlorate
ClO₂^-	chlorite
ClO^-	hypochlorite

phosphorus

cyanide

cations

metal oxyanions

PO₄^3-	phosphate
HPO₄^2-	hydrogen phosphate
H₂PO₄^-	dihydrogen phosphate

CN^-	cyanide
OCN^-	cyanate
SCN^-	thiocyanate

NH₄⁺	ammonium
H₃O⁺	hydronium
Hg₂²⁺	mercury(I)

CrO₄^2-	chromate
Cr₂O₇^2-	dichromate
MnO₄^-	permanganate

oxygen

organics

OH^-	hydroxide
O₂^2-	peroxide

C₂H₃O₂^-

acetate

Common naming practices

If you can remember the formula of the ion whose name ends with ate, you can usually work out the formulas of the other family members as follows:

modify stem name with:	meaning	examples
-ate	a common form, containing oxygen	chlorate, ClO₃^- nitrate, NO₃^- sulfate, SO₄^2-
-ite	one less oxygen than -ate form	chlorite, ClO₂^- sulfite, SO₃^2- nitrite, NO₂^-
per-, -ate	same charge, but contains one more oxygen than -ate form	perchlorate, ClO₄^- perbromate, BrO₄^-
hypo-, -ite	same charge, but contains one less oxygen than the -ite form	hypochlorite, ClO^- hypobromite, BrO^-
thio-	replace an O with an S	thiosulfate, S₂O₃^2- thiosulfite, S₂O₂^2-

Some anions can capture hydrogen ions. For example, carbonate (CO₃^2- 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:	meaning	examples
hydrogen or bi-	(1) captured H⁺ ions	hydrogen carbonate, HCO₃^- (a.k.a. bicarbonate) hydrogen sulfate, HSO₄^- (a.k.a. bisulfate)
dihydrogen	(2) captured H⁺ ions	dihydrogen 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
CO₃^2-	carbonate
CrO₄^2-	chromate
Cr₂O₇^2-	dichromate
HPO₄^2-	hydrogen phosphate
O₂^2-	peroxide
SO₄^2-	sulfate
SO₃^2-	sulfite
S₂O₃^2-	thiosulfate

-3
PO₄^3-	phosphate

Ion	Two-Dimensional Structure	Three-Dimensional Representation
Ammonium NH_₄⁺
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 CO₃^2-
Chromate CrO₄^2-
Dichromate Cr₂O₇^2-
Hydrogen Phosphate HPO₄^2-
Sulfate SO₄^2-
Sulfite SO₃^2-
Thiosulfate S₂O₃^2-

Ion	Two-Dimensional Structure	Three-Dimensional Representation
Phosphate PO₄^3-

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, CO₃^2-	phosphate, PO₄^3-
	bicarbonate, HCO₃^-	chromate,CrO₄^2-
	bisulfate, HSO₄ ^-	dichromate,Cr₂O₇^2-
	bisulfite, HSO₃ ^-	oxalate,C₂O₄^2-
	chlorate,ClO₃^-	peroxide,0₂^2-
	chlorite,ClO₂^-	silicate,SiO₃^2-
	cyanide,CN^-	sulfate,SO₄^2-
	hydroxide,OH^-	sulfite,SO₃^2-
	hypochlorite,ClO^-	tartrate,C₄H₄0₆^2-
	iodate,IO₃^-	thiosulfate,S₂O₃^2-
	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. 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.

Examples:

Al(C₂H₃O₂)₃	- aluminum acetate	KCN	- potassium cyanide
BaSO₃	- barium sulfate	CaSO₃	- calcium sulfite
Li₃PO₄	- lithium phosphate	NH₄OH	- ammonium hydroxide

Multiple Ionic Charges - The ionic charges of several transition metals are variable. For example the copper ion can either be 1+ or 2+.

Table of Metal Ions with Multiple Valence Numbers

antimony (III)	- Sb³⁺	iron (II)	- Fe²⁺	mercury (I)	- Hg₂⁺²
antimony (IV)	- Sb⁵⁺	iron (III)	- Fe³⁺	mercury (II)	- Hg²⁺
chromium (II)	- Cr²⁺	lead (II)	- Pb²⁺	nickel (II)	- Ni²⁺
chromium (III)	- Cr³⁺	lead (IV)	- Pb⁴⁺	nickel (III)	- Ni³⁺
copper (I)	- Cu ⁺	manganese (II)	- Mn²⁺	tin (II)	- Sn²⁺
copper (II)	- Cu²⁺	manganese (IV)	- Mn⁴⁺	tin (IV)	- Sn⁴⁺

The name of the compound should have a roman numeral placed between the name of the cation and the anion to indicate the specific charge of the cation being used. To determine this charge you need to determine what charge is needed to balance the overall compound. To do this multiply the charge of the anion by the number of anions divide this by the number of cations. This will give the charge for the cation.

Examples:

FeO	- iron II Oxide	PbO	- lead II oxide
Fe₂O₃	- iron III oxide	PbO₂	- lead IV oxide
CuOH	- copper I hydroxide	CrNO₃	- chromium II nitrate
Cu(OH)₂	- copper II hydroxide	CrNO₂	- chromium II nitrite

Binary Molecular Formulas - Molecules are compounds that use covalent bonds to join two atoms together. Binary molecules will only have two elements in their formula. An easy way to determine if the compound is named in this manner, is the fact that the two elements in the formula will both be nonmetals (or both are from the right hand side of the periodic table). The names of the compounds will include a prefix to indicate the number of atoms of each element. There is no need to balance this type of formula. The second elements name is changed to end in -ide.

Table of Prefixes

one -	mono	six -	hexa
two -	di	seven -	hepta
three -	tri	eight -	octa
four -	tetra	nine -	nona
five -	penta	ten -	deca

An exception to using the prefixes is when the first element has only one atom. The prefix would be mono is not used for this instance. Also determining where the words fit together will take some practice.

Examples:

CO₂	- carbon dioxide
CCl₄	- carbon tetrachloride
S₃N₂	- trisulfur dinitride

Acids - Acids dissociate into ions when disolved in water. All of the formulas for acids that are dealt with in this section will start with the hydrogen ion. In order to name the compound as an acid, first name the compound as if it were an ionic compound. Use hydrogen as the cation. Then change the name according to the following table.

Table for Naming Acids

Ending of name as an ionic compound	New form of name
-ide	hydro-root-ic acid
-ite	root-ous acid
-ate	root-ic acid

Examples:

Formula	Ionic Name	Acidic Name
HCl	hydrogen chloride	hydrochloric acid
HNO₃	hydrogen nitrate	nitric acid
H₂SO₃	hydrogen sulfite	sulfurous acid

Ions arranged by family

Common naming practices

Ion

Two-Dimensional Structure

Three-Dimensional Representation

Ion

Two-Dimensional Structure

Three-Dimensional Representation

Ion

Two-Dimensional Structure

Three-Dimensional Representation

Ion

Two-Dimensional Structure

Three-Dimensional Representation