What are the Formulae of Ionic Compounds?
Why is the formula of sodium
oxide Na2O
and
not NaO or
NaO2?
The ionic solid must
have the same number
of plus and minus
charges.
If Na+ forms a compound with O2-,
then the formula will be Na2O.
Two sodium ions (each 1+) will be needed
to balance the charge on one
oxygen ion (2-).
Sodium has valency 1, oxygen has
valency 2.
Examples of formulae
of other ionic compounds
from the elements on the previous page are
LiF, LiCl, LiBr, LiI,
1+ with 1-
NaF,
NaCl,
NaBr,
NaI,
gives
KF,
KCl,
KBr,
KI,
1 to 1.
Li2O,
Na2O,
K2O,
1+
with 2-
Li2S,
Na2S,
K2S,
gives 2 to 1.
MgF2, MgCl2, MgBr2, MgI2,
2+
with 1-
CaF2, CaCl2, CaBr2, CaI2,
gives 1 to 2.
MgO, CaO, MgS, CaS, 2+ with 2- gives 1 to 1.
AlF3, AlCl3, AlBr3, AlI3, 3+ with 1- gives 1 to 3.
Al2O3, Al2S3, 3+ with 2- gives 2 to 3.
gcsescience.com Contents The Periodic Table Index Quizzes gcsescience.com
Copyright © 2012 Dr. Colin France. All Rights Reserved.