Ionic Compounds Containing Transition Metals
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1
2Ionic Compounds Containing Transition Metals
The transition metals are the elements located in the middle of the periodic table (in groups 3-
12. Unlike the group 1A and 2A metal ions, the charges of transition metal ions are not easily
determined by their location on the periodic table. Many of them have more than one charge
(also known as an oxidation state). There are eight transition metals that you should highlight
on your periodic table:
Co, Cr, Cu, Fe, Mn, Hg, Sn, and Pb
Each of these elements form more than one ion and therefore must be labeled accordingly.
2+
3+
For example, iron forms two ions: Fe
and Fe
. We call these ions “iron (II) ion” and “iron (III)
ion” respectively. (See “Table of Transition Metal Ions”).
When naming any ion from the elements listed above, you MUST include a Roman numeral in
parentheses following the name of the ion. The this roman numeral is equal to the charge on
the ion. We don’t include the “+” because all metal ions are positive. Here are two more
examples:
4+
3+
Pb
= “lead (IV) ion”
Cr
= “chromium (III) ion
Similarly, when naming a compound containing one of these transition metals, you must
include the Roman numeral as well. “Iron Chloride” isn’t specific enough since the compound
could contain either iron (II) or iron (III) ion. You must specify the charge on the iron.
2+
-
Iron (II) chloride contains the Fe
ion. When combined with chloride, Cl
, we know the formula
must be FeCl
.
2
3+
Iron (III) chloride contains the Fe
ion. This time, three chlorides are required to form a neutral
compound. Therefore, the formula is FeCl
.
3
By looking at the formula of an ionic compound, we can determine the charge (oxidation
state) of the metal.
Example: Write the name of Co
O
2
3
1. Recognize that Co, cobalt, is a transition metal. This means that you must include a Roman
numeral after its name. So, the basic name will be Cobalt (__) Oxide.
2. To find the charge on cobalt, use oxide as a key. Oxide has a charge of –2 so three oxides
will have a charge of –6.
3. What balances a –6 charge? A +6 charge! So, the positive half of the compound must
equal +6.
4. Since there are two cobalt ions, the charge is split between them. So, each one has a +3
3+
charge. Therefore, we are using the Co
ion and the compound is called cobalt (III) oxide.
Remember that anions (negative ions) always have a definite charge. When dealing with
compounds containing transition metals, look to the anion first. Determine the charge of the
anion and then solve to figure out the charge of the cation.
When dealing with metals other than the transition metals, you don’t need Roman numerals. In
2+
other words, calcium ion, Ca
is always +2. Don’t call CaCl
“calcium (II) chloride.” Its name is
2
“calcium chloride.”
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