Unit 6 – Naming Ionic Compounds with Polyatomic Ions
Polyatomic – more than one atom, a molecule
Ion – has an excess or lack of electrons giving an overall charge
Polyatomic Ion – a molecule that has a excess or lack of electrons; has an overall charge
Common polyatomic ions are given on the back of your periodic table.
Except for hydroxide, peroxide, and cyanide, polyatomics do NOT have the –ide ending.
Be careful to tell the difference between a neutral molecule and a polyatomic ion:
SO3 is a molecule; no charge
SO32- is a polyatomic ion; has -2 charge
Compound Names from Formulas with Polyatomic Ions:
How do you know there is a polyatomic ion by looking at the chemical formula?
There are more than 2 elements
1. Write cation name first  name of metal OR ammonium
You must still include Roman numerals, if necessary
2. If anion is a polyatomic ion, just write its name.
3. If the anion is a nonmetal  change name of nonmetal by adding –ide to root word
Compound Formulas from Names of Compounds with Polyatomic Ions:
How do you know there is a polyatomic ion by looking at the name?
Ammonium is the cation name OR
The anion name ends in –ite or –ate OR
The anion is hydroxide, peroxide or cyanide
Write ionic formulas as before, EXCEPT:
1. When writing ions, write the formula of the polyatomic ion EXACTLY as given on
the sheet; NEVER change the chemical formula of a polyatomic ion.
2. More than one of a polyatomic ion  surround the formula with parentheses and
write the subscript outside the parentheses.
3. If subscript of polyatomic ion is one, omit the parentheses.
Practice:
Na2SO4:
magnesium bisulfate:
Fe(NO3)2:
manganese(II) hydroxide:
K2Cr2O7:
ammonium chlorate:
Unit 6 – Naming Ionic Compounds with Polyatomic Ions
Polyatomic – more than one atom, a molecule
Ion – has an excess or lack of electrons giving an overall charge
Polyatomic Ion – a molecule that has a excess or lack of electrons; has an overall charge
Common polyatomic ions are given on the back of your periodic table.
Except for hydroxide, peroxide, and cyanide, polyatomics do NOT have the –ide ending.
Be careful to tell the difference between a neutral molecule and a polyatomic ion:
SO3 is a molecule; no charge
SO32- is a polyatomic ion; has -2 charge
Compound Names from Formulas with Polyatomic Ions:
How do you know there is a polyatomic ion by looking at the chemical formula?
There are more than 2 elements
4. Write cation name first  name of metal OR ammonium
You must still include Roman numerals, if necessary
5. If anion is a polyatomic ion, just write its name.
6. If the anion is a nonmetal  change name of nonmetal by adding –ide to root word
Compound Formulas from Names of Compounds with Polyatomic Ions:
How do you know there is a polyatomic ion by looking at the name?
Ammonium is the cation name OR
The anion name ends in –ite or –ate OR
The anion is hydroxide, peroxide or cyanide
Write ionic formulas as before, EXCEPT:
4. When writing ions, write the formula of the polyatomic ion EXACTLY as given on
the sheet; NEVER change the chemical formula of a polyatomic ion.
5. More than one of a polyatomic ion  surround the formula with parentheses and
write the subscript outside the parentheses.
6. If subscript of polyatomic ion is one, omit the parentheses.
Practice:
Na2SO4:
magnesium bisulfate:
Fe(NO3)2:
manganese(II) hydroxide:
K2Cr2O7:
ammonium chlorate: