Writing formulae for ionic compounds
1
(ii) Simple ionic compounds
The charge on many ions can be worked out from the electron arrangements on page
the Data Booklet.
Group 1
Group 2
Group 3
1 +ve
2 +ve
3 +ve
Group 4
Group 5
Group 6
Group 7
3 -ve
2 -ve
1 -ve
of
In an ionic compound, the charge on all positive ions must balance the charge on all
negative ions.
Since the overall charge is neutral, the formula for an ionic compound can be worked out
by finding the relative number of each ion required to make the overall charge zero.
Example 1: sodium chloride
positive ion
negative ion
Na+
Na+ Cl-
formula
Clor
NaCl
Example 2: potassium oxide
positive ion
negative ion
K+
formula
O2(K+)2O2-
or
K2 O
By balancing the charge on the positive and negative ions, write the chemical formula for
each of the following compounds.
sodium chloride
Chemical Changes and Structure
potassium oxide
Ionic bonding 4
Writing formulae for ionic compounds
2
(ii) Simple ionic compounds
calcium sulphide
radium oxide
lithium iodide
magnesium bromide
rubidium oxide
strontium nitride
Chemical Changes and Structure
Ionic bonding 4