Polyatomic Ions

Compounds&

Nomenclature

Objectives Covered Today

6. Define a polyatomic ion

7. C4.2c Name compounds containing a polyatomic ion.

8. C4.2d Given the name of a compound containing a polyatomic ion, write its formula.

Objective 6

Define a polyatomic ion

Polyatomic Ion: An ion (either positively or negatively charged) composed of two or more atoms.

Is it possible to predict charges?

• Based on covalent bonding (next chapter)• Charges of polyatomic ions are still based on

the overall stability of the molecule• Not as predictable as monatomic ions• These will have to be memorized• However, this becomes easy with practice

Common Examples

HCO32- Bicarbonate Ion

PO43- Phosphate Ion

NH4+ Ammonium Ion

NO3- Nitrate Ion

Objective 7Name compounds containing a polyatomic ion

Example: NaNO3

1.If the compound contains a metal cation, the name of the metal comes first.

Objective 7Name compounds containing a polyatomic ion

Example: NaNO3

1.If the compound contains a metal cation, the name of the metal comes first.

Sodium

Objective 7Name compounds containing a polyatomic ion

Example: NaNO3

2. The second part of the name is just the name of the polyatomic ion

Sodium

Objective 7Name compounds containing a polyatomic ion

Example: NaNO3

2. The second part of the name is just the name of the polyatomic ion

Sodium Nitrate

What if the Polyatomic Ion comes first?

NH4+ (Ammonium ion) is a positive ion while still

being polyatomicIf you are using a polyatomic cation you just use

the ion’s name, and it will be written first

NH4Cl

What if more than one Polyatomic Ion is needed?

Compounds must be neutral!• If > 1 polyatomic ion is needed in a formula, it

will be put in parentheses before the subscript• When writing its name, it will just remain the

name of the polyatomic ionAl2 (SO4)3

Objective 8

Given the name of a compound containing a polyatomic ion, write its formula.

Example: Potassium Carbonate1. Determine atomic symbols and charges

Objective 8

Given the name of a compound containing a polyatomic ion, write its formula.

Example: Potassium Carbonate1. Determine atomic symbols and charges

K+ CO32-

Objective 8

Given the name of a compound containing a polyatomic ion, write its formula.

Example: Potassium Carbonate2. Determine number of each ion to balance charges

K+ CO32-

Objective 8

Given the name of a compound containing a polyatomic ion, write its formula.

Example: Potassium Carbonate2. Determine number of each ion to balance charges

2K+ 1CO32-

Objective 8

Given the name of a compound containing a polyatomic ion, write its formula.

Example: Potassium Carbonate3. Using symbols for both ions and proper subscripts,

write the formula

K2CO3

Practice Examples

1. BeSO3

2.NaC2H3O2

3.Ca(NO3)2

4.Aluminum Nitrite

5.Iron (II) Hydroxide

6.Ammonium Phosphate

Happy Thanksgiving Break!