NAMING IONS AND IONIC COMPOUNDS
(All ions have a charge and compounds do not.)
1. A monatomic ion is composed of only 1 element.
If it is a cation (positive ion), its name is unchanged.
EX: Ca+ 2 is called calcium ion
If it is an anion (negative ion), the ending of its name is changed to ide.
EX: S –2 is the sulfide ion not sulfur
Br - would be ___________
2. A polyatomic ion is composed of 2 or more elements and has a charge. You will
be given a list of polyatomic ion names and their charges.
Sulfate SO4-2
Superscripts indicate charge
Subscripts indicate number of
specific atoms in a molecule or
ion
3. A compound is composed of 2 or more elements and has no overall charge.
4. A binary compound is composed of only 2 elements. EX: CaBr2
5. To name ionic binary compounds, keep the name of the 1st element (positive ion)
and change the name of the 2nd element (negative ion) to its ion name.
EX: NaBr is Sodium bromide not sodium bromine
6. To name an ionic compound with 3 or more elements, the name of the positive ion
stays the same, the remaining elements usually comprise a polyatomic ion.
EX: NaOH is sodium hydroxide and CaCO3 is Calcium carbonate
There is an exception to this. Ammonium (NH4+ ) is a positive polyatomic ion,
and you will need to recognize it as such so that you will not make the mistake of
trying to use nitrogen in its name.
EX: NH4Br is ammonium bromide
7. Practice naming the following compounds:
a. CaCl2
b. BaS
c. KNO2
d. LiI
e. LiOH
f. BeSO4
g. AlPO4
h. NH4I
i. GaN
j MgO
WRITING FORMULAS FOR IONIC COMPOUNDS
To write the formulas for an ionic compound when you know the name:
1. First write the formula for each ion along with its charge.
2. Then crisscross the charges, writing them as subscripts instead of
superscripts. Do not include the + or - sign. “1’s” are omitted.
3. Sometimes a parenthesis will need to be added or subscripts will need to
be reduced. You will be shown examples of this.
Ex 1: Magnesium Bromide
Mg
Br
Mg1
Br2
2+
Mg2+ Br- Ex 2: Magnesium nitrate Mg2+ NO3-
-
-
Mg2+
NO3
Mg1
(NO3) 2
Mg(NO3)2
Mg Br2
Practice writing formulas for the following:
A. Calcium bromide
B. Potassium sulfide
C. Sodium Sulfate
D. Magnesium Nitrate
E. Barium Nitrate
F. Lithium Oxide
G. Ammonium oxide
H. Barium Nitride
Practice naming the following:
a. KCl
b. KBr c. SrO
d. MgCO3 e. Cs NO3
f. NH4SO4
Hydrates
Hydrates are solid compounds that contain water in a definite ratio.
To name hydrates you must know the following prefixes.
1 mono
6 hexa
2 di
7 hepta
3 tri
8 octa
4 tetra
9 nona
5 penta
10 deca
To write the formula for Calcium chloride trihydrate,
Namine Ionic Compounds that contain Cations Having Multiple
Charges
Some elements (usually transition metals) have more than one possible
charge. To name compounds with these elements you must indicate the
charge of the element with a roman numeral following its name.
Ex. CuBr is Copper I Bromide
and
CuBr2 is Copper II Bromide
How do you know which Roman numeral to use? First, determine the
total charge for the negative ion. The sum of the charges of the positive
ion must be equal to the charges for the negative ion. (Overall charge
must be zero.)
Ex:
Cu Br2
Cu ? Br2 -1 x 2 atoms
= -2
? + -2 = 0
must equal +2 for overall charge
of atom to be zero
Copper II Bromide
Ex.
Cu2 O
Cu2? O -2 x 1 atom = -2
? + -2 = 0
? equal + 2 but there are 2 atoms indicated in
the formula, so +2/2 atoms of Copper
= +1
Copper I Oxide
Some elements with more than one charge are
Copper
Manganese
Mercury
Cobalt
Tin
Iron
Zinc
Lead
Chromium
Practice naming these:
1. SnCl2
4. MnSO4
2. Zn3P
5. Hg2O
3. CrI2
6. Pb(SO4)2