Naming Compounds
My Goals for this Lesson:

Apply the rules of nomenclature to name a compound, when given its formula.

Write the formulas for ionic and covalent compounds from their names.
I’m preparing to understand and to be able to name compounds and write formulas for ionic and covalent
compounds.
Names and titles can be very important. When you have more than one friend
with the same first name, you need to use their last names or nicknames to
tell them apart.
In chemistry, some compounds have nicknames or common names such as baking soda, water,
laughing gas, and table salt. However, these common names do not tell you anything about the
chemical composition of the substance. It is important to use systematic names to help us
identify a chemical formula from a name or vice versa, in order to communicate in a chemistry
course or in a scientific setting.
Being familiar with how chemical compounds are named also allows you to be a more
knowledgeable consumer. You will soon be able to read, with more knowledge, the labels on food,
cleaning supplies, and other substances you encounter every day.
Chemical Formulas
Fill in the blanks using the lesson.
A chemical formula is used to show the
formula show the number of each
show the
of a compound. The subscripts in a molecular
of atom in a compound, while the subscripts in a formula unit
of cations to anions in an ionic crystal.
Fill in this table using the interactive section from the Lesson.
Compound
Elements in the compound
H=
O=
Al =
N=
O=
(The group NO2 is called what?)
Number of each element
H=
O=
Al =
N=
O=
Show the math of multiplying
subscripts for each atom and for
the group with NO2.
Binary Ionic Compounds
Fill in the blanks using the lesson.
As you have learned, a metal forms a positive ion (
The
and
) and a nonmetal forms a negative ion (
).
combine to form an ionic compound. This type of ionic compound is more
specifically referred to as a binary ionic compound.
To name a binary ionic compound, there is a standard process. As practice, let’s look at naming the
compound CaCl2. The steps are as follows:
1. Look at the first element in the formula. Ca is the symbol for Calcium. The names of the elements
are found on the periodic table. The first word in the binary ionic compound name is Calcium.
2. Take the name of the nonmetal. Cl would be the nonmetal because it is second in the chemical
formula. It is the symbol for the element Chlorine. Shorten Chlorine to its root word Chlor-.
3. Add –ide to the root word. In this case, Chlor- would add with –ide to form Chloride.
Examples
Fill in the table using the Examples in the lesson.
Compound Formula
Name of the metal
(cation)
ROOT name of
nonmetal (anion)
Name of Compound
NaCl
CaBr2
Al2O3
Polyatomic Ions
In order to name ionic compounds that contain polyatomic ions, you must know the names of the common
polyatomic ions. Use this copy of the polyatomic ion list from the course to help you learn the name and
charge of these ions.
Be careful, because some of the ions have similar names (sulfate and sulfite, nitrate and nitrite, etc.)!
The polyatomic ions have already been given specific endings for their names, so you do not need to
change their endings when naming ionic compounds that contain any of these ions. This means that if
the negative ion in the compound is a polyatomic ion, just name the polyatomic ion—do not change its
ending to -ide.
Fill in the table using the Examples in the Let’s Practice section of the lesson.
Compound Formula
Name of the cation
Name of the anion
Name of Compound
NaOH
(NH4)2S
Compound Name
Symbol of the cation
Symbol of the anion
Compound Formula
calcium sulfate
aluminum nitrate
Ions with Roman Numerals/Transition Metals
You know the charges of the ions formed from elements in groups 1–2 and 13–17, but what about the
elements that can form more than one possible charge? The transition metals in the d block, as well as
tin (Sn) and lead (Pb), can form more than one possible charge as positive ions. Two different systems
are used for naming such ions.
The system which we will use in this course uses Roman numerals to represent the charge of the
ion in the compound’s name.
Examples
Fill in the table using the Examples in the lesson.
Compound Name
One:
Write out
each element
with its ion
charge.
copper (I) oxide
Cu+ O2-
Two:
Move the superscripts to
the subscript of the
opposite element
(Remember that the
charges are dropped when
performing this action).
Three:
Reduce ratios
if possible.
Four:
Write the
formula name.
Subscript ratio
is reduced.
Cu2O
copper (II) oxide
lead (II) chloride
iron (II) oxide
Compound Formula
Fe2(SO4)3
Name of the cation
Iron
Possible charges of cation
2+ or 3+
Name of anion
(nonmetal or polyatomic ion)
Sulfate
Charge of the anion
2-
subscript of cation x charge (c) +
subscript of anion x charge = 0
2 x c + 3 x -2 = 0
2c + -6 = 0
2c = 6
c=3
Name of Compound
iron (III) sulfate
CrF3
PbSO4
Binary Covalent Compounds
Compounds between nonmetals are almost always molecular instead of ionic. Because nonmetals can often
combine in more than one ratio, the subscripts have to be represented in the name of each compound.
You have already seen this type of naming with two common compounds: carbon monoxide (CO) and
carbon dioxide (CO2). Notice that the name tells you how many oxygen atoms are in each of those
compounds. Prefixes are used to represent the subscript (not a charge, as with the Roman numerals in
ionic formulas) on each of the elements in the molecule. If there is only one atom of the first element in
the compound, no prefix is used. On the other hand, a prefix is always used for the second element, even
if there is only one atom like in carbon monoxide.
Naming Binary Covalent Compounds
1. Prefix to represent the number of atoms of the first element (ONLY
needed if there is more than one)
+
2. Name of the first element (the lesser electronegative of the two)
+
3. Prefix to represent the number of atoms of the second element
+
4. Root name of the second element
+
5. Ending changed to –ide
The -o or -a at the end of a prefix is often dropped before another vowel. Ex: monoxide and pentoxide
Practice
Use the interactive section from the lesson to complete this chart.
Compound
Formula
# of
atoms of
1st
element
CO2
1
N2O
SO3
NO
CF4
P2O5
N2O3
Prefix for
this #
Name of
1st
element
# of atoms
of 2nd
element
None needed
with only 1
Carbon
2
Prefix for
this #
Name of
2nd
element
with –ide
ending
Compound
name
di-
Oxide
Carbon
dioxide
Acids
When dissolved in water, certain molecules produce a solution containing free H+ ions. These molecules,
called acids, are a distinct class of chemical compounds that you will be learning more about throughout
this course. Acids are covalently bonded molecules that separate into positive hydrogen ions and
negative nonmetal ions or polyatomic ions in water. The rules for naming acids depend on whether the
acid contains any oxygen
Oxyacids
Oxyacids are acids that contain hydrogen, oxygen, and a third element. Many of the common polyatomic
ions are produced by the loss of the hydrogen ions from oxyacids. This is why the name of the
polyatomic ion is used in the name of the oxyacid as well.
1. If the polyatomic ion’s name ends in –ate, change the ending to –ic to name the oxyacid. Notice
that the prefix hydro- is not added to the beginning of the name. This is to differentiate
between binary acids and oxyacids, like hydrosulfuric acid (H2S) and sulfuric acid (H2SO4).
Steps:
I. Look at the formula. Oxyacids contain hydrogen, oxygen, and a third element
II. Refer to the polyatomic ion list
III. If a polyatomic ion ends in –ate, change the ending to –ic
IV. The name is then: polyatomic ion + –ic ending + acid
Examples
Fill in this table using the examples from the Lesson page.
Compound
Formula
HClO3
HNO3
H2CO3
H3PO4
List the elements
(need H, O and 3rd
element)
H, Cl and O
Name the
polyatomic ion
Change the –ate
to –ic
Add Acid to complete
the compound name
chlorate
chloric
chloric acid
2. If the polyatomic ion’s name ends in –ite, change the ending to –ous to name the oxyacid.
Steps:
I. Look at the formula. Oxyacids contain hydrogen, oxygen, and a third element
II. Refer to the polyatomic ion list
III. If a polyatomic ion ends in –ite, change the ending to –ous
IV. The name is then: polyatomic ion + –ous ending + acid
Examples
Fill in this table using the examples from the Lesson page.
Compound
Formula
HClO2
HNO2
H2SO3
List the elements
(need H, O and 3rd
element)
H, Cl and O
Name the
polyatomic ion
Change the –ite to
–ous
Add Acid to complete
the compound name
chlorite
chlorous
chlorous acid
Be sure to do the additional practice problems in the Review box at the bottom of the Lesson page
AND the 2 practices on the Activity page.
This flow chart for naming from the Review might help as well.
HONORS ONLY SECTION
What Is a Hydrate?
Answer the following questions using the Honors section of the lesson.
Define a hydrate as used in chemistry.
How do we indicate a compound is a hydrate in the formula for that compound?
How do hydrates appear?
What can happen to their appearance as the water is removed?
List all terms used to describe a hydrate compound that has had the water removed.
Naming Hydrates
The water is not part of the chemical substance, but it is contained within the crystal, so this is
reflected in the unique way the formula is written.
Example: CuSO4 · 5 H2O
This formula means that for every one mole of CuSO4 formula units in the crystal, there are five moles
of water molecules.
The dot is not a multiplication sign but shows that the two formulas are connected.
To name a hydrate:
1. Name the ionic compound using the rules that you have already learned. This includes using a
Roman numeral and/or polyatomic ion name where appropriate.
2. Name the chemically bound water molecules using a prefix (the same prefixes used for naming
covalent compounds) and the word hydrate.
The hydrate above, CuSO4 · 5 H2O, is named copper (II) sulfate pentahydrate. The prefix penta- means
five, and the word hydrate represents water. Explore the formula below to see how the name is created.
Be sure to do the extra practice on the Honors page of the lesson for this naming skill.