 When learning
about Ionic Formulas and how one goes about constructing them, one must remember that ions
are are atoms or molecules that has gained or lost one or more electron (e-). This number
is key to understanding the concept of writing ionic formulas.There are many uses if
uses of ions in chemistry there are ionic bonds, ionic compounds, ionic radius, ionization
constant, ionization energy, all are useful terms and can be referred to by the
definitions column on the left hand column,
When one wants to
learn how to write an Ionic formulas one must carefully identify the elements that are
being done within the reaction, then we go about identifying what the oxidation number is
and if it is polyatomic.
Example:
Common table
salt, NaCl, is made from sodium, Na and Cl. They both have charges and are written as
follows:
Na+1 Cl -1
To confirm that
this formula is correct we observe its oxidation numbers (one positive and the other
negative) in this situation both oxidation numbers are equal, thus there is no
additional work to be done since they form to become a stable compound (neutral) and the
formula for table salt is agreed upon NaCl.
However when we
get into harder degrees of writing these ionic reactions we have to put together elements
that have different charges and in order to make the compound neutral we have to balance
the charges and change the subscripts.
When writing the
formula for a compound made up of aluminum ion and the sulfate ion we write;
Al +3 and SO4 -2
To
make the sum of the charges equal to zero, we must detect the least common multiple of 3
and 2. The least common multiple is 6. It is necessary to have two Al +3 and three in the compound to maintain neutrality. Writing two aluminum ions
in the formula is simple.
(Al)2
For
the sulfate , the entire polyatomic ion must be put in parenthesis and on the outside
include the three sulfate ions on the outside.
(SO4)
3
Thus,
the aluminum sulfate has the formula Al2(SO4)3 (Parenthesis are used in a formula only when you are expressing multiples of
a polyatomic ion. If you only one sulfate ion were needed in writing formula, parentheses
would not be used.
Hints and Tips:
Note that the numbers that are in red are the ions' charges.
2. When forming a compound the positive must ALWAYS
be placed before the negative NO EXCEPTIONS!!
3. When a compound is unbalanced it becomes unbalanced and unstable.
4. the
entire polyatomic ion must be placed in parenthesis to indicate that there are already a
number of ions required
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Last Modified February 07, 2008 |
