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Chapter 5 Ionic Compounds

5.4

Polyatomic Ions

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Copyright © 2008 by Pearson Education, Inc.

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Polyatomic Ions

A polyatomic ion

  • Is a group of atoms.
  • Has an overall ionic charge.

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Some examples of polyatomic ions are

NH4+ ammonium OH− hydroxide

NO3− nitrate NO2− nitrite

CO32− carbonate PO43− phosphate

HCO3− hydrogen carbonate

(bicarbonate)

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Some Compounds with Polyatomic Ions

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More Names of Polyatomic Ions

The names of common polyatomic anions

  • Some end in ate.

NO3− nitrate PO43− phosphate

  • Some end in ite.

NO2− nitrite PO33− phosphite

  • Some will have hydrogen in name (or bi).

HCO3− hydrogen carbonate (bicarbonate)

HSO3− hydrogen sulfite (bisulfite)

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Names and Formulas of Common Polyatomic Ions

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Publishing as Benjamin Cummings

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Names and Formulas of Common Polyatomic Ions

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Copyright © 2008 by Pearson Education, Inc.

Publishing as Benjamin Cummings

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Prefixes for Names of Polyatomic Ions of Halogens

Similar polyatomic ions will have similar names.

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ClO4− perchlorate one oxygen more

ClO3− chlorate most common form

ClO2− chlorite one oxygen less

ClO− hypochlorite two oxygens less

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Parentheses

  • If you need two or more Polyatomic ions, YOU MUST USE Parentheses with the subscript.
  • Write the formula for Cu+2 and NO3-1

You need 1 Cu+2 and 2 NO3-1

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You would write it like this: Cu(NO3)2

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The 2 tells us we need 2 of the NO3-1 ions.

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Naming Compounds with Polyatomic Ions

  • The positive ion is named first followed by the name of the polyatomic ion.

NaNO3 sodium nitrate

K2SO4 potassium sulfate

Fe(HCO3)3 iron(III) bicarbonate

or iron(III) hydrogen carbonate

(NH4)3PO3 ammonium phosphite

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Some Compounds with Polyatomic Ions

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Table 5.7

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Learning Check

Select the correct formula for each:

A. aluminum nitrate

1) AlNO3 2) Al(NO)3 3) Al(NO3)3

B. copper(II) nitrate

1) CuNO3 2) Cu(NO3)2 3) Cu2(NO3)

C. iron (III) hydroxide

1) FeOH 2) Fe3OH 3) Fe(OH)3

D. tin(IV) hydroxide

1) Sn(OH)4 2) Sn(OH)2 3) Sn4(OH)

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Solution

Select the correct formula for each:

A. aluminum nitrate

3) Al(NO3)3

B. copper(II) nitrate

2) Cu(NO3)2

C. iron(III) hydroxide

3) Fe(OH)3

D. tin(IV) hydroxide

1) Sn(OH)4

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Learning Check

Match each formula with the correct name:

A. MgS 1) magnesium sulfite

MgSO3 2) magnesium sulfate

MgSO4 3) magnesium sulfide

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B. Ca(ClO3)2 1) calcium chlorate

Ca(ClO)2 2) calcium chlorite

Ca(ClO2)2 3) calcium hypochlorite

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Solution

Match each formula with the correct name:

A. MgS 3) magnesium sulfide

MgSO3 1) magnesium sulfite

MgSO4 2) magnesium sulfate

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B. Ca(ClO3)2 1) calcium chlorate

Ca(ClO)2 3) calcium hypochlorite

Ca(ClO2)2 2) calcium chlorite

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Learning Check

Name each of the following compounds:

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A. Mg(NO3)2

B. Cu(ClO3)2

C. PbO2

D. Fe2(SO4)3

E. Ba3(PO3)2

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Solution

Name each of the following compounds:

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A. Mg(NO3)2 magnesium nitrate

B. Cu(ClO3)2 copper(II) chlorate

C. PbO2 lead (IV) oxide

D. Fe2(SO4)3 iron(III) sulfate

E. Ba3(PO3)2 barium phosphite

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Writing Formulas with Polyatomic Ions

The formula of an ionic compound

  • Containing a polyatomic ion must have a charge balance that equals zero(0).

Na+ and NO3− → NaNO3

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  • With two or more polyatomic ions encloses the polyatomic ions in parentheses.

Mg2+ and 2NO3− → Mg(NO3)2

subscript 2 for charge balance

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Learning Check

Write the correct formula for each:

A. potassium bromate

B. calcium carbonate

C. sodium phosphate

D. iron(III) oxide

E. iron (II) nitrite

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Solution

Write the correct formula for each:

A. potassium bromate KBrO3

B. calcium carbonate CaCO3

C. sodium phosphate Na3PO4

D. iron(III) oxide Fe2O3

E. iron (II) nitrite Fe(NO2)2

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Naming Ionic Compounds

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Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Table 5.8

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Flowchart for Naming

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Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

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Learning Check

Name the following compounds:

A. Ca3(PO4)2

B. FeBr3

C. Al2S3

D. Mn(NO2)2

E. NaHCO3

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Solution

Name the following compounds:

A. Ca3(PO4)2 Ca2+ PO43− calcium phosphate

B. FeBr3 Fe3+ Br − iron(III) bromide

C. Al2S3 Al3+ S2− aluminum sulfide

D. Mn(NO2)2 Mn2+ NO2− manganese(II) nitrite

E. NaHCO3 Na+ HCO3− sodium hydrogen carbonate

or sodium bicarbonate

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Learning Check

Write the formulas for the following:

A. calcium nitrate

B. iron(II) hydroxide

C. aluminum carbonate

D. copper(II) bromide

E. lithium phosphate

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Solution

Write the formulas for the following:

A. calcium nitrate Ca2+, NO3− Ca(NO3)2

B. iron(II) hydroxide Fe2+, OH− Fe(OH)2

C. aluminum carbonate Al3+, CO32− Al2(CO3) 3

D. copper(II) hypobromite Cu2+, Br- CuBr2

E. lithium phosphate Li+, PO43− Li3PO4

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