Ionic and Covalent Compounds (Combining and Naming)
I hope this helps our understanding of ionic and covalent compounds. Again,
these notes are a tool that you must learn to use. We will do many examples in
class, but it is still your responsibly to study. As always I am here for additional
assistance.
Using your periodic table of Ions we can see that most of elements (with the
exception of some transition metals and all the noble gases) have at least one
ionic form. Many in this table have two common forms shown.
Two examples are shown below:
The box on the right shows only one ionic form for Nitrogen (The nitride
ion)
The box on the left shows the two common ionic forms of element Iron
(Iron II and Iron III)
3+
3- Fe
N 2+
Fe
You have also been given a slightly abbreviated version of the complex ions table
that appears at the top of the Periodic Table of Ions. It is both shorter and easier
to read. You will be allowed to use this on the test. Again, it is a tool and you must
understand its use.
A) Combining Ions to form compounds – a step-by-step process to gain
understanding
For this example we will use the compound Cobalt III oxide, but these steps
will apply in all cases as we take a compound name and write the CORRECT
formula.
1) First identify the positive ion (it is ALWAYS LISTED FIRST). So In the
example above Cobalt III is what we are looking for.
2) Use the periodic table of ions; you will discover Cobalt has two ionic
forms. However, we have identified the ion we desire in the name. The
Cobalt III ion has a +3 charge (All elements with multiple forms will be
identified by the + charge that each holds – examples Iron II (+2),
Manganese IV (+4), Nickel III (+3) etc.
3) Write down the ion!
3+
Co
4) We must now identify and locate the negative ion. In this case it is oxide.
a. It is found in group VIA and looks like this:
2-
O
5) Write it down next to the previous ion (Cobalt III)
3+ 2-
Co O
6) Knowing that compounds cannot have an net charge (be -/+) we must
combine in a ratio that creates the same number of +’s as –‘s.
7) The simplest way to accomplish this is to do the following: Take the
exponent from the Cobalt III ion and use it as the subscript for oxide,
and take the exponent for Oxide ion and use it for the subscript for
Cobalt.
3+ 2-
Co O
Which results in this:
Co2O3
This is the correct compound Cobalt III oxide
These steps can be followed in all cases that we will be dealing with. One note
subscripts should be reduced to least common factor when necessary. Example:
Iron II oxide Iron II (Fe2+), oxide (O2-)
2+ 2-
Fe O
Fe2O2 FeO
This is the correct compound Iron II oxide
These steps work for complex ions as well!
Example: Ammonium Chromate
#1 & # 2 (Ammonium from our list = NH4+)
+
# 3 NH4
#4 (Chromate from our list Cr2O72-)
+ 2-
#5 & #6 NH4 Cr2O7
+ 2- 4 2 7
#7 NH4 Cr2O7 (NH )2Cr O
You notice that when complex ions have a subscript they MUST have parenthesize
to identify the ion correctly!
From a compound to a name we just reverse the process!
Practice, Practice, Practice and you will see just now easy this can be!