Naming Ionic Compounds
Names of Ionic Compounds
1.
Identify the ions
2.
Name the cation
3.
Name the anion
The ions are named in the same order that they
are written in the formula. Name only one cation
and only one anion.
Identify the Ions
formula Na Cl Al2S3 Fe F3 Cu3(PO4)2 (NH4)2SO3
Each of our ionic compounds will
contain one kind of cation and one
kind of anion (underlined at left).
If the ionic compound has only
two elements, each is usually a
monatomic ion.
If the compound has more than
two elements, there is usually at
least one polyatomic ion.
Identifying Ions Examples
formula
Notice that
subscript numbers
are part of the
compound formula
(white numbers) or
are part of the
polyatomic ions (colored numbers)
cation
anion
NaCl
Na1+
Cl1-
Al2S3
Al3+
S2-
FeF3
Fe3+
F1-
Cu3(PO4)2
Cu2+
PO43-
(NH4)2SO3
NH41+
SO32-
Ion Names Examples
formula
cation
anion
NaCl
Na1+
sodium ion
Cl1-
Al2S3
Al3+
aluminum ion
FeF3
Fe3+
iron(III) ion
Cu3(PO4)2
Cu2+
copper(II) ion
(NH4)2SO3
NH41+ ammonium ion
formula
cation
chloride ion
NaCl
Na1+
sodium ion
Cl1-
chloride ion
S2-
sulfide ion
Al2S3
Al3+
aluminum ion
S2-
sulfide ion
F1-
fluoride ion
FeF3
Fe3+
iron(III) ion
F1-
fluoride ion
PO43-
phosphate ion
Cu3(PO4)2
Cu2+
copper(II) ion
PO43-
phosphate ion
SO32-
sulfite ion
(NH4)2SO3
NH41+ ammonium ion
SO32-
sulfite ion
Polyatomic Ions Examples
formula
cation
NaCl
Na1+
Monatomic Ion Examples
anion
sodium ion
Cl1-
chloride ion
Al2S3
Al3+
aluminum ion
S2-
sulfide ion
FeF3
Fe3+
iron(III) ion
F1-
fluoride ion
Cu3(PO4)2
Cu2+
copper(II) ion
PO43-
phosphate ion
(NH4)2SO3
NH41+ ammonium ion
SO32-
sulfite ion
anion
Compound Names are formed
by combining Ion Names
formula
cation anion
NaCl
Al2S3
FeF3
Cu3(PO4)2
(NH4)2SO3
name
cation
anion
sodium chloride
aluminum sulfide
iron(III) fluoride
copper(II) phosphate
ammonium sulfite
Monatomic Cation Names
The name of
each monatomic
cation is the
same as the
name of the
element. A
roman numeral
indicates the
cation’s charge,
when there is
more than one
possibility.
formula
cation anion
NaCl
Al2S3
FeF3
Cu3(PO4)2
(NH4)2SO3
name
cation
anion
sodium chloride
aluminum sulfide
iron(III) fluoride
copper(II) phosphate
NaCl
Al2S3
There is only
one polyatomic
cation common
in compound
naming. That is
ammonium ion.
FeF3
Cu3(PO4)2
(NH4)2SO3
The name of
each monatomic
anion is the
same as the
name of the
element but
with an -ide
suffix.
ammonium sulfite
Polyatomic Cation Names
formula
cation anion
Monatomic Anion Names
name
cation
anion
sodium chloride
aluminum sulfide
iron(III) fluoride
copper(II) phosphate
ammonium sulfite
formula
cation anion
NaCl
Al2S3
FeF3
Cu3(PO4)2
(NH4)2SO3
name
cation
anion
sodium chloride
aluminum sulfide
iron(III) fluoride
copper(II) phosphate
ammonium sulfite
Polyatomic Anion Names
There are a
numerous
polyatomic
anions. Most
have names
with -ate or -ite endings.
This always
indicates that
oxygen is part
of the ion.
formula
cation anion
NaCl
Al2S3
FeF3
Cu3(PO4)2
(NH4)2SO3
name
cation
anion
sodium chloride
aluminum sulfide
iron(III) fluoride
copper(II) phosphate
ammonium sulfite
Ion Charges and Naming
Ion charges must be used to write ionic formulas, but
naming compounds often does not require using their
charges.
Na1+
sodium ion
Cl1-
chloride ion
Al3+
aluminum ion
S2-
sulfide ion
Fe3+
iron(III) ion
F1-
fluoride ion
Cu2+
copper(II) ion
PO43-
phosphate ion
ammonium ion
SO32-
sulfite ion
NH4
1+
Specifying charge
formula
To name ionic
compounds
such as these,
we must
indicate the
charge of the
cation. Roman
numerals are
the simplest
way to do this.
name
FeF2
iron(II) fluoride
FeF3
iron(III) fluoride
Cu3PO4
copper(I) phosphate
Cu3(PO4)2
copper(II) phosphate
SnO
tin(II) oxide
SnO2
tin(IV) oxide
When to specify charge
Charge affects
the name when
the compound
contains a
cation which
has different
charges in
different
compounds.
formula
NaCl
Al2S3
FeF3
Cu3(PO4)2
(NH4)2SO3
name
sodium chloride
aluminum sulfide
iron(III) fluoride
copper(II) phosphate
ammonium sulfite
How do we know when to specify
the charge?
!
By learning which cations can have more than one
charge. The following ions will be used during this
course:
copper (1+, 2+); iron (2+, 3+); chromium (2+, 3+); tin (2+, 4+); and lead (2+, 4+).
How can we know the charge of
the cation in a particular
formula?
!
Remember when we write a neutral formula, the
total number of positives must equal the total
number of negatives. In formula writing the charges of the ions are used
to determine the number of ions that make positives
and negatives equal. Al3+
S2-
2(3+)=3(2-)
Al2S3
How can we know the charge?
!
In naming, the number of ions in the formula can be
used to determine the unknown charge. In the
example below, the formula tells us that there is
one Sn ion and there are two O ions. O is in group
6A and therefore oxide ion’s charge is 2-. So the
only unknown number is the charge of Sn. !
SnO2
1(?)=2(2-)
Examples for you to try.
How can we know the charge?
!
Since the total number of positives must equal the
total number of negatives, the charge of tin ion
must be 4+.
SnO2
1(?)=2(2-)
1(4+)=2(2-)
tin(IV) oxide
Remember: Number of cations(charge) = Number of anions(charge)
FeF3
CrSO4
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Cu3(PO4)2
Pb3N4
!
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! Check answers in the video.