Unit V: Nomenclature of Polyatomic Ions

Unit VA: The "Basic Eight" Polyatomic Ions

In this unit you are asked to memorize the names and formulas of 8 polyatomic ions, to start with. You will be asked to learn more later on. "Learning" means memorizing the correct spelling of the name, the correct subscript(s) and charge of each ion.

1+	1-	2-	3-
NH4^+ ammonium	C2H3O2^- acetate*	CO3^2^- carbonate	PO4^3^- phosphate
	NO3^- nitrate	SO4^2^- sulfate
	OH^- hydroxide
	ClO3^- chlorate

*acetate is also written as CH₃CO₂^-

In memorization, it helps to look for patterns. Note that all but two of the ions have the ending "- ate". For the ions with a charge of 1- , look up where the first element of each ion is located on the period table (C, N, O, Cl). Study the formulas and names of this group of ions before moving on to ions with a charge of 2- . Again look up the location of the first element of each ion in the periodic table (C and S). Study these two names and formulas, and finally move to the ion with a charge of 3- . Look up the position of P in the periodic table. After you have studied each group based on charges, put them on flash cards and test yourself over and over.

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Drill I - 1: Nomenclature of the "Basic Eight" Polyatomic Ions

NAME	FORMULA	FORMULA	NAME
sulfate		OH^-
acetate		SO4^2^-
chlorate		NH4^+
ammonium		NO3^-
phosphate		ClO3^-
carbonate		PO4^3^-
hydroxide		C2H3O2^-
nitrate		CO3^2^-

To check your answers, note that you are at Drill I-1.

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NOMENCLATURE OF COMPOUNDS OF THE BASIC EIGHT POLYATOMIC IONS

The rules for naming and writing formulas for polyatomic ions are the same as for the monatomic ions (see Unit VI). The only difference is if (and only if) there is more than one polyatomic ion, parenthesis must be used to avoid confusion.

For example, magnesium nitrate is Mg(NO₃)₂. Since Mg is in Group IIA, it has a charge of 2+ and nitrate has a charge of 1- (from memory), to obtain a net charge of zero, there must be two nitrate ions for every magnesium ion. In the case of potassium acetate, since potassium is in Group IA, it must have a charge of 1+, and acetate has a charge of 1- , the formula is simply KC₂H₃O₂. No parenthesis is necessary.

Drill I - 2: Nomenclature of Compounds of the "Basic Eight" Polyatomic Ions With Cations of Fixed Charges:

NAME	FORMULA	FORMULA	NAME
sodium carbonate		K3PO4
strontium carbonate		Ca(NO3)2
aluminum sulfate		(NH4)2SO4
ammonium phosphate		Al(OH)3
aluminum chlorate		LiC2H3O2
potassium sulfate		MgCO3
calcium acetate		Ba(ClO3)2

To check your answers, note that you are at Drill I-2.

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In naming compounds with cations of variable charges, the charge of the cation must be deduced from the charge of the anions. It is therefore imperative that you have learned the charges of the ions presented in Units VA and VB. For example, MnSO₄ should be named manganese (II) sulfate. Since you had previously memorized the fact that SO₄^2-has a charge of 2- , the manganese ion must have a charge of 2+. In the case of Cu(NO₃)₂, since the nitrate ion has a charge of 1- , two nitrates would have a total charge of 2- . Thus Cu must have a charge of 2+. The name for Cu(NO₃)₂ is therefore Cu(II) nitrate or cupric nitrate.  The following drill lets you practice with cations of variable charges.

Drill I - 3: Nomenclature of Compounds of the "Basic Eight" Polyatomic Ions With Cations of Variable Charges:

iron(II) carbonate	Cu2CO3
iron(III) carbonate	CuCO3
copper(I) sulfate	SnSO4
cobalt(II) phosphate	Fe3(PO4)2
chromium(III) chlorate	Hg(C2H3O2)2
tin(IV) sulfate	BiPO4
antimony(III) acetate	Mn(ClO3)2

To check your answers, note that you are at Drill I-3.

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Now that you have learned some ions with -ide endings, and some with -ate endings, it might be wise for you to go through the following drill that includes some of the ones with -ide endings.

Drill I - 4: Compounds of the "Basic Eight" Polyatomic Ions and –ide ions With Cations of Both Fixed and Variable Charges:

(Learning to distinguish between those that require Roman numerals and those that do no.)

calcium phosphate	Na3N
chromium(III) sulfide	NaNO3
potassium carbonate	K2SO4
magnesium acetate	CdCO3
chromium(III) hydroxide	FeCl2
aluminum chlorate	BaCl2
Lead(IV) selenide	NH4NO3
copper(II) nitride	Mn(ClO3)2
Iron(II) nitrate	Cu3PO4

To check your answers, note that you are at Drill I-4.

Answers to Drills I-1 through I-4

Drill I - 1: Nomenclature of the "Basic Eight" Polyatomic Ions;

sulfate	SO4^2^-	OH^-	hydroxide
acetate	C2H3O2^-	SO4^2^-	sulfate
chlorate	ClO3^-	NH4^+	ammonium ion
ammonium	NH4^+	NO3^-	nitrate
phosphate	PO4^3^-	ClO3^-	chlorate
carbonate	CO3^2^-	PO4^3^-	phosphate
hydroxide	OH^-	C2H3O2^-	acetate
nitrate	NO3^-	CO3^2^-	carbonate

Drill I - 2: Nomenclature of Compounds of the "Basic Eight" Polyatomic Ions With Cations of Fixed Charges:

sodium carbonate	Na2CO3	K3PO4	potassium phosphate
strontium carbonate	SrCO3	Ca(NO3)2	calcium nitrate
aluminum sulfate	Al2(SO4)3	(NH4)2SO4	ammonium sulfate
ammonium phosphate	(NH4)3PO4	Al(OH)3	aluminum hydroxide
aluminum chlorate	Al(ClO3)3	LiC2H3O2	lithium acetate
potassium sulfate	K2SO4	MgCO3	magnesium carbonate
calcium acetate	Ca(C2H3O2)2	Ba(ClO3)2	barium chlorate

Drill I - 3: Nomenclature of Compounds of the "Basic Eight" Polyatomic Ions With Cation of Variable Charges:

iron(II) carbonate	FeCO3	Cu2CO3	copper(I) carbonate
iron(III) carbonate	Fe2(CO3)3	CuCO3	copper(II) carbonate
copper(I) sulfate	Cu2SO4	SnSO4	tin(II) sulfate
cobalt(II) phosphate	Co3(PO4)2	Fe3(PO4)2	iron(II) phosphate
chromium(III) chlorate	Cr(ClO3)3	Hg(C2H3O2)2	mercury(II) acetate
tin(IV) sulfate	Sn(SO4)2	BiPO4	bismuth(III) phosphate
antimony(III) acetate	Sb(C2H3O2)3	Mn(ClO3)2	manganese(II) chlorate

Drill I - 4: Compounds of the "Basic Eight" Polyatomic Ions and -ide ions With Cations of Both Fixed and Variable Charges:

(Learning to distinguish between those that require Roman numerals and those that do not.)

calcium phosphate	Ca3(PO4)2	Na3N	sodium nitride
chromium(III) sulfide	Cr2S3	NaNO3	sodium nitrate
potassium carbonate	K2CO3	K2SO4	potassium sulfate
magnesium acetate	Mg(C2H3O2)2	CdCO3	cadmium(II) carbonate
chromium(III) hydroxide	Cr(OH)3	FeCl2	iron(II) chloride
aluminum chlorate	Al(ClO3)3	BaCl2	barium chloride
lead(IV) selenide	PbSe2	NH4NO3	ammonium nitrate
copper(II) nitride	Cu3N2	Mn(ClO3)2	manganese(II) chlorate
iron(II) nitrate	Fe(NO3)2	Cu3PO4	copper(I) phosphate