Writing Formulas for Ionic Compounds
General Rules
1.
Write each ion symbol with charge: simple ions from
front of periodic table; complex on back.
2.
Find lowest common denominator for the charges of
the 2 ions. For each ion, multiply the ion charge by a
number that will give the common denominator. The
following must apply:
Total positive charge = total negative charge.
Write in the correct subscripts after each ion symbol
– this will be the number of each ion that are needed
to have charges equal. Use lowest whole number
ratios.

Cations come first in the formula, anions come
second.
Naming Ionic Compounds
General Rules:
 Name each ion
o Cations are named first in the formula, anions
are named second.
Types of Ions and Ionic Compounds
There are 4 different types of ions that may be found in
Ionic compounds.
A. Monatomic Ions (Simple Ions)
 Single atoms that have lost or gained one or more
electrons
 Form Binary Ionic Compounds (2 simple ions)
 Eg. Na+
Cl-
B. Polyatomic Ions (Complex Ions)
 Cations or anions composed of a group of atoms with a
net positive or negative charge
Eg. NH4+
NO2NO3CO32-
Ammonium ion
Nitrite ion
Nitrate ion
Carbonate ion
C. Multivalent Ions
 certain transition metals can form more than one type of
ion, each with a different charge
 Eg. Fe3+
Fe2+
 The more commonly occurring ion is listed on top, thus
Fe3+ is more common than Fe2+
D. Hydrated Ionic Compounds
 Water molecules are loosely held within the ionic
compound
 Eg. ZnCl2 • 6H2O
CuSO4 • 5H2O
Monoatomic Ionic Formulas
Examples
silver chloride
aluminum oxide
barium fluoride
lithium sulfide
magnesium nitride
Monoatomic Ionic Compound Names
 NOTE:
When naming monotomic ionic compounds, the cation
retains metal name, and the anion name ends in "ide"
Examples
Ca3P2
AlCl3
BeI2
Al2S3
BaBr2
Writing Formulas for Polyatomic Ionic Compounds
The same general rules apply, however:

If more than one complex ion is present, place
brackets around it, then give its subscript.
Examples:
ammonium nitrate
NH4NO3
potassium carbonate
K2CO3
sodium thiosulfate
Na2S2O4
lithium hydrogen carbonate
LiHCO3
Naming Polyatomic Ionic Compounds
The same general rules apply, where cations are named first
in the formula, anions are named second, however:
 Note: Names of polyatomic ions are on the back of
the periodic table at the top
Examples:
Na3BO3
sodium borate
(NH4)2CO3
ammonium carbonate
Na2Cr2O7
sodium dichromate
KCrO4
potassium chromate
Writing Formulas for Multivalent Ionic Compounds
The same general rules apply, however:

The Roman numerals indicate the charge on the
multivalent ion.
Examples:
Roman Numerals
iron(II)sulfide
lead(IV)oxide
gold (IV) phosphide
uranium (VI) oxide
I = one
II = two
III = three
IV= four
V = five
VI = six
VII = seven
Naming Multivalent Ionic Compounds
The same general rules apply, however:

You must use Roman numerals in the name to
indicate charge of the particular multivalent ion
Examples:
FeO
V3N5
AuCl3
CrBr3
Writing Formulas for Hydrated Ionic Compounds
The same general rules apply, however:

Numbers and the formula “ · ___H2O” will be used
to indicate the number of water molecules are
given in the name of the hydrated ionic compound.
Numerical Prefixes
1 = mono 2 = di
3 = tri
6 = hexa 7 = hepta 8 = octa
4 = tetra 5 = penta
9 = nona 10 = deca
Examples:
zinc chloride hexahydrate
sodium chlorite heptahydrate
lithium nitrite pentahydrate
nickel (II) bromide decahydrate
Naming Hydrated Ionic Compounds
The same general rules apply, however:

Numerical prefixes and the word “______hydrate”
will be used to indicate the number of water
molecules given in the formula.
Examples:
Ba(OH)2 · 8H2O
Na2Cr2O7 . 5 H2O
AgNO3 . 4H2O
FeSO4 . 5H2O