Chemical Formulas & Chemical Compounds

Writing and Naming Formulas For Ionic Compounds with Polyatomic

ions

ObjectiveLearn how to write and name compounds with

polyatomic ions

Ionic Compounds containing Polyatomic ions

• Some ionic compounds contain polyatomic ions.

• Groups of atoms that are covalently bonded and have a charge.

Polyatomic Ions

• Most polyatomic ions are anions

• Most of these are oxyanions– Contain oxygen

• Sometimes a group of elements can form more than one oxyanion

Common Polyatomic ions

What’s up with the ate and ite?

• Ex: PO4-3 and PO3

-3

• The greater number of oxygen atoms – ends in “ate” (PO4

-3 phosphate)

• The fewer number of oxygen atoms – ends in “ite” (PO3

-3 phosphite)

Name these Polyatomic ions

• NO3 -1

• SO4 -2

• SO3-2

• NH4+1 this is the only polyatomic cation

Write formulas with polyatomic ions

• Look at the ions and balance their charges, create the formula. (The easiest way to balance charges is to criss cross them)

• If there is more than one polyatomic ion in the formula put ( ) around it and the subscript for the polyatomic ion on the outside of the ( ).

• Ex: Mg+2 PO4-3 Mg3 (PO4)2

Write formulas with polyatomic ions

Mg+2 PO4-3

Mg+2 (PO4)-3

Mg3 (PO4)2

Try another one

K+1 NO3-2

K+1 (SO3)-2

K2 (SO3)1 you don’t need to write the ( ) or #1

K2 SO3

Write these formulas• Li+1 NO3 -1

• Mg+2 SO4 -2

• Ca+2 SO3-2

• Na+1 PO4-3

• Al+3 HCO3-1

Naming Ionic Compounds with Polyatomic Ions

• Just like in monatomic ionic compounds, NAME THE CATION WITH THE ELEMENTS NAME

• NAME A MONOATOMIC ANION BY CHANGING THE ENDING TO “ide”

• The polyatomic ion has its own name and that DOES NOT CHANGE

• Ex: Li+1 NO3 -1 LiNO3

lithium nitrate

Naming Ionic Compounds with Polyatomic Ions

• Ca(HCO3)2

• This compound comes from the Ca+2 ion and the HCO3

-1 ion

• Ca(HCO3)2

• calcium hydrogen carbonate

• Just name the parts. No Name Changes

You Try• NH4 NO3 (Hint: this compound has two polyatomic ions)

• Sr3(PO4)2

 

• Zn(NO2)2

• MgCO3

Answers will be given in class