Polyatomic Ions Notes
Polyatomic Ions


Polyatomic ions are ions that contain two or more atoms.
o NH4+
o CO32In a polyatomic ion, the charge belongs to the entire ion.
Polyatomic Ions – Formula Writing


There is only one difference to writing a chemical formula of a compound
containing a polyatomic ion:
o If you need more than one polyatomic ion, you put brackets around the
polyatomic ion, and place the subscript outside the brackets.
Write the formula for Cu+2 and NO3-1
Examples:
A. aluminum nitrate
B. copper(II) nitrate
C. iron (III) hydroxide
D. tin(IV) hydroxide
Polyatomic Ions – Compound Naming

The positive ion is named first.
o Check to see if it is a metal with more than one charge.
o Check to see if it is polyatomic, for example ammonium (NH4+).

The polyatomic ion is then named.
o There is an alphabetical list of polyatomic ions on the back of your
periodic table.
Examples
 NaNO3:
sodium nitrate
 K2SO4 :
potassium sulfate
 Fe(HCO3)3:
iron(III) bicarbonate or iron(III) hydrogen carbonate
 (NH4)3PO3
ammonium phosphite
Use the formula to write the name:
1. MgS
2. MgSO3
3. MgSO4
4. Ca(ClO3)2