We’ll go over the method of naming ionic compounds that have one or more
polyatomic ions.
Any time a formula has more than
two elements in it, or more than
two capital letters,
Any time a formula has more than two elements in it, or more than two capital letters,
Any time a formula has more than
two elements in it, or more than
two capital letters, it must contain at least
one polyatomic ion.
it must contain at least one polyatomic ion.
MgSO4
Al(NO3)3
Lets consider the formula MgSO4,
NH4ClO3
MgSO4
3 Elements
Al(NO3)3
NH4ClO3
It has 3 elements in it: magnesium, sulphur, and oxygen, so it must contain a polyatomic ion.
Formulas and Charges of Common Ions
The polyatomic ions that we’ll be using in this course are shaded on this table. If we are given a formula
with more than 2 elements in it, we look on this table for any polyatomic ions that are in the formula.
Formulas and Charges of Common Ions
MgSO4
The formula we’re working with is MgSO4,
Formulas and Charges of Common Ions
MgSO4
SO4 in the formula (click) is from the polyatomic ion sulphate, SO4 2
minus
Formulas and Charges of Common Ions
MgSO4
Mg in the formula is from (click) the single metal ion Mg 2+
MgSO4
Polyatomic
Al(NO3)3
Ion
So MgSO4 contains the polyatomic ion sulphate, SO4.
NH4ClO3
Al(NO3)3
MgSO4
Now we’ll consider the formula Al, NO3 in brackets, 3
NH4ClO3
Al(NO3)3
MgSO4
3 Elements
NH4ClO3
This formula also contains 3 elements, (click) aluminum, nitrogen, and oxygen. So it must have a
polyatomic ion in it.
Formulas and Charges of Common Ions
Al(NO3)3
The formula we’re working with is Al(NO3)3
Formulas and Charges of Common Ions
Al(NO3)3
We see that NO3 in the formula (click) is from the polyatomic ion nitrate,
NO3 minus.
Formulas and Charges of Common Ions
Al(NO3)3
And The Al in the formula
Formulas and Charges of Common Ions
Al(NO3)3
Is from the single metal ion Al 3plus
Al(NO3)3
Polyatomic
MgSO4
Ion
So Al(NO3)3 contains the polyatomic ion nitrate NO3
NH4ClO3
NH4ClO3
MgSO4
4 Elements
We see that this formula contains 4 elements: (click) Nitrogen, hydrogen, chlorine, and oxygen
Formulas and Charges of Common Ions
NH4ClO3
The formula we’re working with is NH4ClO3.
Formulas and Charges of Common Ions
NH4ClO3
Looking on the table, we see that NH4 in the formula,
Formulas and Charges of Common Ions
NH4ClO3
Comes from the positive polyatomic ion ammonium, NH4 plus
Formulas and Charges of Common Ions
NH4ClO3
And ClO3 in the formula
Formulas and Charges of Common Ions
NH4ClO3
Comes from the negative polyatomic ion chlorate, ClO3 minus
NH4ClO3
2 Polyatomic
MgSO4
Ions
So the formula NH4ClO3 contains 2 polyatomic ions, (click) NH4 or ammonium, and ClO3, or
chlorate.
Rules for Naming Compounds
with Polyatomic Ions
Now that we’ve shown you how to find polyatomic ions in formulas, lets
look at the rules for naming compounds with polyatomic ions.
Rules for Naming Compounds
with Polyatomic Ions
1. The name of a polyatomic ion does not
change when it is used in a compound name.
2. Single elements follow the same naming
rules as they do in other compounds.
The first rule is, the name of a polyatomic ion does not change in any way when it is used in a
compound name. Its name is the same in a compound as it is on an ion table.
Rules for Naming Compounds
with Polyatomic Ions
1. The name of a polyatomic ion does not
change when it is used in a compound name.
2. Single elements follow the same naming
rules as they do in other compounds.
The second rule is, single elements that are not in polyatomic ions, follow
the same rules as they do in other compounds.
Name the compound with the formula NH4Br
The best way to learn how to name compounds with polyatomic ions, is to see
several examples. Here, we’re asked to name the compound NH4Br
Name the compound with the formula NH4Br
NH4Br
3 Elements
We see that NH4Br has 3 elements (click) nitrogen, hydrogen, and bromine.
Therefore, it must contain a polyatomic ion.
Name the compound with the formula NH4Br
NH4Br
Looking on the table, we see that NH4 in the formula,
Name the compound with the formula NH4Br
NH4Br
Is from the polyatomic ion ammonium, NH4 plus.
Name the compound with the formula NH4Br
NH4Br
ammonium bromide
Names of polyatomic ions don’t change when they are part of a compound name, so
the first part of the name (click), is ammonium.
Name the compound with the formula NH4Br
NH4Br
ine
ammonium bromide
The formula ends with the single element Br
Name the compound with the formula NH4Br
NH4Br
ine
ammonium bromide
Which the periodic table tells us is bromine.
Name the compound with the formula NH4Br
NH4Br
ine
ammonium bromide
So we’ll note down bromine here.
Name the compound with the formula NH4Br
NH4Br
For a non-metal at
the end of a
formula, the name
ends in “ide”
ine
ammonium bromide
But for a non-metal element at the end of a formula, the name must be changed to
end in –ide.
Name the compound with the formula NH4Br
NH4Br
ine
ammonium bromide
ide
So we replace the “ine” with “ide”
Name the compound with the formula NH4Br
NH4Br
ide
ammonium bromide
And we’re left with the name bromide.
Name the compound with the formula NH4Br
On the
ion table
NH4Br
ide
ammonium bromide
Alternately, we can find Br minus on the ion table, and we see that it’s name is bromide,
so if a non-metal ion is on our ion table, we can just copy the name directly from there.
Name the compound with the formula NH4Br
NH4Br
ide
ammonium bromide
So the final answer is (click) the name of this compound is ammonium bromide