Polyatomic Ionic Formulas

Polyatomic Ions

• What does NH4+ mean?

Ion contains: 1 Nitrogen

Overall Charge: +1

NIon contains: 4 Hydrogens

H H

H H

+

Symbols for Polyatomic Ions

Symbol:

NH4+

Ion Charge

This charge applies to the ENTIRE ION

Writing Formulas – Equal Charges

• If the charge on the cation and anion are ________, drop the charges and put the two ions together

equal

Example) Al3+ PO43- AlPO4

Polyatomic Ions – Unequal Charges

• Let’s just look at an example with a polyatomic ion.

Write the ionic formula for:

Barium Nitrate What’s the problem?

How could we fix it?

Writing Ionic Formulas-Polyatomic Ions

STEP1) Write the cation

first, then the anion.

EXAMPLEBarium Nitrate

Ba2+ NO3-

Same as before

Writing Ionic Formulas – Polyatomic Ions

STEP2) Put parenthesis ( )

around the polyatomic ion or ions.

Leave the charge on the outside!

EXAMPLEBarium Nitrate

Ba2+ (NO3)-

New Step!!

Writing Ionic Formulas – Polyatomic Ions

STEP3) Drop the + and –

(but NOT the numbers!!)

EXAMPLE

Same as before

Barium Nitrate

Ba2 (NO3)1

Writing Ionic Formulas – Polyatomic Ions

STEP4) Cross the charges.

Leave the crossed charges on the outside!!

EXAMPLEBarium Nitrate

Ba2 (NO3)1

Ba1(NO3)2

Same as before – with a twist!!

Barium Nitrate

Ba1(NO3)2

Writing Ionic Formulas – Polyatomic Ions

STEP5) Drop any “1”.

ALSO: If you drop a “1” for a polyatomic ion, you may also drop parenthesis ( )

EXAMPLE

Ba(NO3)2

Same as before – with a twist!!

Another Look

• What does this mean?

Ba(NO3)2

1 Ba 2 SETS of NO3

1 Ba 2 N

6 O

Writing Ionic Formulas-Polyatomic Ions

STEP1) Write the cation

first, then the anion.

EXAMPLEAmmonium Phosphate

NH4+ PO4

3-

Same as before

Writing Ionic Formulas – Polyatomic Ions

STEP2) Put parenthesis ( )

around the polyatomic ion or ions.

Leave the charge on the outside!

EXAMPLE

New Step!!

Ammonium Phosphate

(NH4)+ (PO4)3-

Writing Ionic Formulas – Polyatomic Ions

STEP3) Drop the + and –

(but NOT the numbers!!)

EXAMPLE

Same as before

Ammonium Phosphate

(NH4)1 (PO4)3

Ammonium Phosphate

(NH4)1 (PO4)3

Writing Ionic Formulas – Polyatomic Ions

STEP4) Cross the charges.

Leave the crossed charges on the outside!!

EXAMPLE

(NH4)3(PO4)1

Same as before – with a twist!!

Ammonium Phosphate

(NH4)3(PO4)1

Writing Ionic Formulas – Polyatomic Ions

STEP5) Drop any “1”.

ALSO: If you drop a “1” for a polyatomic ion, you may also drop parenthesis ( )

EXAMPLE

(NH4)3PO4

Same as before – with a twist!!

Magnesium Hydroxide

Writing Ionic Formulas – Polyatomic Ions

EXAMPLE

Mg(OH)2

Mg2+

OH-Mg2+

(OH)-Mg2

(OH)1Mg1(OH)2

Lead (IV) Carbonate

Writing Ionic Formulas – Polyatomic Ions

EXAMPLE

Pb(CO3)2

Pb4+

CO32-Pb4+

(CO3)2-Pb4

(CO3)2

Pb2(CO3)4

Silver Chlorate

Writing Ionic Formulas – Polyatomic Ions

EXAMPLE

AgClO3

Ag+ ClO3

-

Notice: The cation charge is +1 and the anion is -1

Names – Example 1

(NH4)2O

NH4+ O2-

Ammonium Oxide

Names – Example 2

BaCrO4

Ba2+ CrO42-

Barium Chromate

Names – Example 3

Fe2(C2O4)3

Fe3+ C2O42-

Iron (III) Oxalate

Names – Example 4

K3PO4

K+ (PO4)3-

Potassium phosphate

Group Practice

• Ionic Formulas and Names – Polyatomic Ions – Group Practice

Group Practice - CheckStation Cation Anion Ionic

FormulaIonic Name

1 Aluminum CO32-

2 NH4+ PO4

3-

3 Ba2+ Nitrate

4 Iron (III) SO32-

5 Li+ BrO3-

6 NH4+ Nitride

Group Practice - CheckStation Cation Anion Ionic

FormulaIonic Name

7 Cu2+ CO32-

8 Al3+ Phosphate

9 Pb2+ OH-

10 Pb4+ SO32-

Group Practice - CheckStation Cation Anion Ionic

FormulaIonic Name

1 Al3+ CO32- Al2(CO3)3 Aluminum

carbonate2 NH4

+ PO43- (NH4)3PO4 Ammonium

Phosphate3 Ba2+ Nitrate Ba(NO3)2 Barium Nitrate4 Iron (III) SO3

2- Fe2(SO3)3 Iron (III) Sulfite5 Li+ BrO3

- LiBrO3 Lithium Bromate6 NH4

+ N3- (NH4)3N Ammonium nitrate

Group Practice - CheckStation Cation Anion Ionic

FormulaIonic Name

7 Cu2+ CO32- CuCO3 Copper (II)

Carbonate8 Al3+ PO4

3- AlPO4 Aluminum Phosphate

9 Pb2+ OH- Pb(OH)2 Lead (II) Hydroxide

10 Pb4+ SO32- Pb(SO3)2 Lead (IV) Sulfite

Group Practice - Check

1) (NH4)3N Ammonium Nitrate

2) FeSO3 Iron(II) Sulfite

3) Fe2(SO3)3 Iron(III) Sulfite

4) KNO3 Potassium Nitrate

5) Cd3(BO3)2 Cadmium Borate

Independent Practice

• Ionic Formulas and Names – Polyatomic Ions – Individual Practice

• Let me know if you have any questions!!!