Name ___________________________________ Date ______________________ Class ______________________
Chapter 9 – Chemical Names and Formulas
Naming Compounds
Naming Ions
For metal ion: use the element name with the word “ion” written after it. The word “ion” MUST be included to
distinguish the ion from the element
Examples:
Na+1 sodium ion
Ca+2 calcium ion
Al +3 aluminum ion
For nonmetal ions: the element name is given an –ide ending.
Examples:
C-4 carbide ion
F-1 fluoride ion
Ion Name
lithium ion
magnesium ion
sodium ion
carbon ion
boron ion
Ion Symbol
Ion Symbol
N-3
O-2
Au+1
C-4
I-1
Br-1
bromide ion
Ion Name
Naming Binary Ionic Compounds When Given the Chemical Formula
**For naming binary ionic compounds, write the name of the cation first, then write the name of the anion using the
–ide ending. The word “ion” is not used when writing compound names. Also, no reference is made to any numerical
subscripts that may be in the formula.
Examples:
NaCl sodium chloride
Na3N sodium nitride
CaCl2 calcium chloride
Formula
KF
BaS
Li2O
ZnCl2
Ba3N2
Compound Name
Formula
CaO
Al2O3
Mg3P2
Na2N
CaBr2
Compound Name
Writing Binary Ionic Formulas When Given the Compound Name
When writing formulas for binary ionic compounds, first write the ions with the correct charges. Then write the
element symbols without the charges, placing the metal first. Now balance the electrical charges. The net charge on
the compound must be zero. (Ask yourself: how many positive charges are needed to balance the negative charges?)
**For any ionic compound, the total number of positive charges MUST balance the total number of negative charges.
The net charge MUST be zero.
First, write the ion symbol over the name of each ion. (This will help you learn the names and correct formulas for each
of the ions!) Then write the correct formula.
Examples:
Na+1
Cl-1
Ba+2 F-1
K+1
O-2
Sodium chloride NaCl
Barium fluoride BaF2
Potassium oxide K2O
Compound Name
calcium phosphide
magnesium oxide
barium nitride
aluminum phosphide
Formula
Compound Name
potassium chloride
lithium fluoride
sodium sulfide
silver chloride
Formula
Most of the transition metals and some of the metals in groups 13, 14, 15 and 16 can form ions with more than one
charge. This variation in charge occurs because the transition metal atoms may use one or more of their d sublevel
electrons as a valence electron, or, in the case of metals in groups 13-16, sometimes only the p sublevel valence
electrons are lost.
The following are examples of metals that form ions having more than one charge. Only the more common charges
have been given here (some may form ions having other charges). You have a sheet with this information also.
Fe2+
Fe3+
Pb2+ lead (II) ion
Pb4+ lead (IV) ion
iron (II) ion
iron (III) ion
Mn2+
Mn3+
manganese (II) ion
manganese (III) ion
Naming Compounds Containing Ions That Have More Than One Charge
To name such compounds, simply follow the rule for naming binary ionic compounds: name the cation first,
then name the anion. The only difference is that you MUST include the Roman numeral for the charge of the cation.
Remember that the anions have fixed charges.
Example 1: In the formula MnO, the manganese ion has a +2 charge and the oxide has a -2 charge. The compound is
called manganese (II) oxide.
Example 2: In the formula CuS, the copper ion has a charge of +2 (there is only one copper ion and there is one sulfide
ion with a charge of -2, so the copper ion must have a charge of +2). The compound is named copper (II) sulfide.
Formula
MnO
PbO2
Fe2O3
Cu3P2
SnF2
Compound Name
Writing Formulas for Ions That Have More Than One Charge
To write the formula when given the name of a compound, write the symbol for each ion above its name first. Then
write a balanced formula.
Example:
Cu+2
S2Cu+1
S-2
Copper (II) sulfide CuS
Copper (I) sulfide Cu2S
Compound Name
copper (I) oxide
lead (II) chloride
Cobalt (II) chloride
mercury (II) bromide
mercury (I) oxide
Formula
Compound Name
iron (II) oxide
lead (IV) oxide
cobalt (III) chloride
mercury (I) bromide
mercury (II) oxide
Formula
As the name suggest, polyatomic ions contain many atoms. A polyatomic ion is an ion consisting of two or more atoms
chemically bonded together by covalent bonds and carrying a net electric charge. Remember the definition of an ion: an
atom or molecule that has gained or lost one or more valence electron and has become a charged particle. Polyatomic
ions are molecules that have become ions. Almost all polyatomic ions carry a negative charge. The original molecules
have gained electrons. The exception is the ammonium ion, NH41+. The ammonium ion is a polyatomic ion that carries a
positive charge. The ammonium ion is formed when an ammonia molecule, NH3, forms a coordinate covalent bond with
a hydrogen ion, H+1. The ammonia molecule doesn’t lose electrons but rather gains a positively charged particle: the
single proton of the hydrogen ion. It is this “additional” proton – or rather the additional positive charge – that gives the
ion its 1+ charge.
Writing Formulas Containing Polyatomic Ions
The polyatomic ion behaves as a SINGLE UNIT. Treat the formula of a polyatomic ion as you would an ion of a
single atom. Remember, the total number of positive charges must equal the total number of negative charges. There
is a zero net charge on the ionic compound. NEVER CHANGE THE FORMULA OF A POLYATOMIC ION: DO NOT OMIT OR
CHANGE ANY SUBSCRIPT IN THE FORMULA!!
Example 1: Na+1 + SO4-2 there is one positive charge and one negative charge; therefore, only one of each ion is
required: NaOH. Notice that the symbols of the ions involved are written with no space between them writing Na OH is
incorrect.
Example 2: Na+1 + SO4-2 there is one positive charge, but there are two negative charges; therefore, two positive ions
are needed to balance the negative charges: Na2SO4. Again, notice the placement of the symbols of the ions and
subscript. The formula is not written Na2 SO4. Be very careful when writing formulas of compounds.
So far so good; But in the examples above, only one polyatomic ion was involved. How do we write the formula
of a compound that requires MORE than one polyatomic ion? Figure out how many total positive and total negative
charges are needed, and how many of each ion are needed. Then use parentheses () around the entire polyatomic
formula and write the necessary subscript OUTSIDE the parentheses.
Example 1: Ca2+ + OH-1
required: Ca(OH)2.
Here we have two positive charges and only one negative charges. Two negative ions are
Example 2: Al3+ + OH-1
Al(OH)3.
Here we have three positive charges and one negative charge. Three positive ions are needed:
And what do we do if the positive ion is a polyatomic ion and the negative ion is also a polyatomic? NOTHING
DIFFERENT!! Use parentheses!! Just remember to treat the polyatomic ions as single units.
Example 1: NH4+1 + OH-1
only one of each ion is needed: NH4OH.
Example 2: NH41+ + CO32-
two ammonium ions are needed to balance the charge on the carbonate ion: (NH4)2CO3.
OH-1
Li+1
NH4+1
Pb+2
Fe+3
NO3-1
SO4-2
PO4-3
C2H3O2-1
Writing Names from Formulas Containing Polyatomic Ions
Now that you can write the formulas of compounds containing polyatomic ions, let’s try naming the compounds
from the formulas. And then we’ll write formulas from the names of compounds. Name each ion in the formula. Do
not include any reference to the subscripts either in the polyatomic ion formula or in the compound formula.
Examples:
NaOH is sodium hydroxide
(NH4)2S is ammonium sulfide
Formula
LiOH
FeSO4
NH4F
(NH4)3PO4
Co(OH)2
Pb(OH)4 is lead (IV) hydroxide
Compound Name
Compound Name
sodium sulfate
copper (I) phosphate
barium hydroxide
iron (II) phosphate
magnesium phosphate
Formula
Compound Name
potassium hydroxide
copper (II) phosphate
ammonium carbonate
iron (III) sulfate
ammonium phosphate
Formula
Writing Names and Formulas for Molecular Compounds:
Molecular compounds are composed of two or more nonmetals, and do NOT contain ions.
Examples:
sulfur dioxide, SO2
carbon dioxide, CO2
sulfur trioxide, SO3
dihydrogen monoxide, H2O
carbon monoxide, CO2
glucose, C6H12O6
As you can see, very often, Greek prefixes are used in the names of compounds having more than one atom of a given
element. The general rules for naming binary (having two elements) molecular compounds are:
1. If there is only one atom of the first element, no prefix is used:
Examples: CO, carbon monoxide
SO3, sulfur trioxide
ClO7, chlorine heptoxide
2. If there are two or more atoms of the first element, the appropriate prefix is used.
Examples: N2O, dinitrogen monoxide
P2O5, diphosphorus pentoxide
3. For the second element, a prefix is always used to indicate the number of atoms present; -ide ending is used for
the second element.
Examples: see examples given for rules 1 and 2.
Common prefixes and their meanings:
mono- (one)
di- (two)
tri- (three)
tetra- (four)
penta- (five)
hexa- (six)
hepta- (seven)
octa- (eight)
nona- (nine)
deca- (ten)
HINT: The final vowel in a prefix is often dropped before a vowel in a stem word: mono- and oxide become monoxide;
tetra- and oxide becomes tetroxide.
Formula
N 2O
N 2O 5
PCl5
N 2O 4
PCl3
Compound Name
dichlorine monoxide
chlorine trifluoride
sulfur hexafluoride
Compound Name
Formula
Compound Name
chlorine dioxide
chlorine heptoxide
dihydrogen monoxide
Formula
An acid is a compound that produces H+ ions in an aqueous (water) solution. A base is a compound that produces OHions in an aqueous solution.
Naming Acids
Acids not containing a polyatomic ion (or oxygen) are named by using hydro- plus the root of the anion plus –ic plus
acid. Acids containing oxygen are named by using the polyatomic root plus –ic if the original polyatomic name contained
–ate or plus –ous if the original root was –ite. If there is sulfur in the polyatomic –ur is added before the –ic or –ous. If
there is a phosphorus in the polyatomic –or is added before the –ic or –ous. These are summarized below.
1.
2.
3.
4.
5.
If no oxygen: hydro + anion root + ic + acid (example – HCl is hydrochloric acid).
If oxygen present: polyatomic root + ic (replacing –ate ending) + acid (example HClO3 – chloric acid).
If oxygen present: polyatomic root + ous (replacing –ite ending) + acid (example HClO2 – chlorous acid).
If sulfur present: polyatomic root + ur + ic/ous + acid (example H2SO4 – sulfuric acid).
If phosphorus present: polyatomic root +or + ic/ous + acid (example H3PO4 – phosphoric acid).
Formula
HBrO
H2CO3
HCl
H3PO3
HF
Compound Name
Writing Formulas for Acids
To write the formula for an acid look at the name. Reverse the process and change the endings to find out
which root anion or polyatomic ion you are dealing with. Next, balance the negative charges with hydrogen.
Example 1: periodic acid…root polyatomic would be periodate or IO41- so balance that with hydrogen to get HIO4.
Example 2: thiosulfuric acid…root polyatomic would bethiosulfate or S2O32- so balance that with hydrogen to get H2S2O3.
Compound Name
hydrosulfuric acid
nitric acid
bromous acid
sulfuric acid
thiosulfuric acid
Formula
Compound Name
chromic acid
hydroiodic acid
nitrous acid
perchloric acid
dichromic acid
Formula
Naming Bases
A base is composed of a metal and an OH- ion. You name the metal and then the OH- with hydroxide.
Ammonia, NH3 is a base. When ammonia is put into water it forms ammonium, NH4 and gives off OH- ions.
NH3 + H2O → NH4+ + OH-.
Examples:
NaOH is sodium hydroxide
Formula
KOH
Fe(OH)2
Al(OH)3
Mg(OH)2
LiOH
Fe(OH)3 is iron (III) hydroxide
Compound Name
Writing Formulas for Bases
To write the formula for bases simply write the formula like you would for an ionic compound. Write the
formula for the metal ion, using Roman numerals where needed, then the formula for hydroxide. Balance the formula
and you’re done.
Compound Name
zinc hydroxide
iron (III) hydroxide
chromium (II) hydroxide
beryllium hydroxide
calcium hydroxide
Formula
Compound Name
silver hydroxide
nickel (II) hydroxide
sodium hydroxide
aluminum hydroxide
copper (III) hydroxide
Formula
Name ___________________________________ Date ______________________ Class ______________________
Prefixes:
1 = mono
2 = di
3 = tri
4 = tetra
5 = penta
6 = hexa
7 = hepta
8 = octa
9 = nona
10 = deca
Roman numerals:
1 = I 6 = VI
2 = II 7 = VII
3 = III 8 = VIII
4 = IV 9 = IX
5 = V 10 = X
START HERE
Is the compound an
acid?
to write formulas
NO
YES
Work the ending
backward then balance
with hydrogen.
Does the compound
have prefixes?
NO
YES
The compound is ionic.
More information is
needed
The compound is
molecular .
1) Does the name have
Roman numerals?
2) Does the name have
polyatomic ions? (think
-ate or -ite endings)
3) No Roman numerals
or polyatomic ions
Roman numeral gives
charge on metal cation.
Use the polyatomic ion
chart for formula and
charge.
Use the periodic table
(of ions) for charges
Balance charges using
criss cross method
(using parenthesis if
needed)
Use the prefixes to
write the name.
- ide  hydro__ic acid
-ate  __ic acid
-ite  __ous acid
Prefixes:
1 = mono
2 = di
3 = tri
4 = tetra
5 = penta
6 = hexa
7 = hepta
8 = octa
9 = nona
10 = deca
Roman numerals:
1 = I 6 = VI
2 = II 7 = VII
3 = III 8 = VIII
4 = IV 9 = IX
5 = V 10 = X
START HERE
Is the first element
hydrogen (H)?
to write names
NO
YES
Are there more than
two elements?
NO
The compound contains a
polyatomic ion - usually
ends in -ate or -ite
Is the first element a
metal?
Does the cation need a
Roman numeral? (look for
split boxes on the periodic
table)
Find the anion name
and change the ending
- ide  hydro__ic acid
YES
Does the cation need a
Roman numeral? (look for
split boxes on the periodic
table)
NO
Use prefixes to name
YES
The compound is
binary - name ends in
-ide
NO
The compound is
binary covalent
The compound is an
acid
Name the ions - cation
first then anion.
YES
NO
Name the ions - cation
first then anion.
Name the ions using
Roman numerals for
the metal cation.
-ate  __ic acid
-ite  __ous acid
YES
Name the ions using
Roman numerals for
the metal cation.