Ch. 15 and 6 Polyatomic Ions

Polyatomic Ions• Tightly bound groups of atoms that behave as

a unit and carry a charge.

Ammonium NH4

+Cyanide

CN-

Sulfite SO3

2-

Examples:

Common Polyatomic Ionswith a -1 charge

• ClO-1 hypochlorite• ClO2

-1 chlorite• ClO3

-1 chlorate• ClO4

-1 perchlorate• CN-1 cyanide• MnO4

-1 permanganate• NO3

-1 nitrate• NO2

-1 nitrite

-1 polyatomic ions cont.

• OH-1 hydroxide• HCOO-1 formate• HCO3

-1 hydrogen carbonate

• HSO3-1 hydrogen sulfite

• HSO4-1 hydrogen sulfate

• CH3COO-1 or C2H3O2-1 acetate

-2 polyatomic ions

• C2O4-2 oxalate

• CO3-2 carbonate

• Cr2O7-2 dichromate

• CrO4-2 chromate

• SO4-2 sulfate

• SO3-2 sulfite

-3 polyatomic ion

• PO4-3 phosphate

• PO3-3 phosphite

+1 polyatomic ions

• NH4+1 ammonium

• H3O+1 hydronium

B. Examine RelationshipsA. Most end in –ite / -ate

Trick to remember: The bigger number ate the little number!

Polyatomic Ions

SO42-

SulfateSO3

2-

Sulfite

The big number ate the little number!

PO43-

PhosphatePO3

3-

Phosphite

NO3-

NitrateNO2

-

Nitrite

Writing Formulas for Ternary Ionic Compounds

A. Contain a polyatomic ion

B. Same rules as for binary ionic compounds.One addition – Use parenthesis if there is

more than one polyatomic ion• Examples:• Calcium Hydroxide– Calcium - Ca2+ OH- –Hydroxide

– Formula for compound – Ca(OH)2

• Boron acetateB3+ C2H3O2

-1

B(C2H3O2)3

• Magnesium Dichromate

Mg+2 Cr2O7-2

Mg2(Cr2O7)2

MgCr2O7

Examples (cont.)

• Magnesium Nitrate–Magnesium – Mg2+

–Nitrate - ????

–Write the formula for the compound

Practice Problems

Write formulas for the following ternary ionic compounds:

a. Calcium Carbonateb. Potassium Sulfatec. Barium Nitrited. Magnesium Phosphate

CaCO3

K2SO4

Ba(NO2)2

Mg3 (PO4)2

Naming Ternary Ionic Compounds

• Same rules as for naming binary ionic compounds:– Name the cation – Use a Roman numeral if

necessary– Name the anion– Do not use the word “ion” in the compound name

Practice Problems:

• Name the following ternary ionic compounds:

a. NaCNb. KClOc. Li2SO3

d. CaC2O4

e. Al(OH)3

f. Sn3(PO4)2

Sodium cyanide

Potassium hypochlorite

Lithium sulfite

Calcium oxalate

Aluminum hydroxide

Tin (II) phosphate

Ionic Compounds- Polyatomic IonsDue at the end of class, Completed

Cl OH SO4 PO4 NO3

Zn+2

NH4

K

Ca

Fe+3

-1-1 -2 -3-1

+

+

+2