Multivalent Metals and Ionic Compounds
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The transition elements are generally multivalent. This means they can form more than one kind of
ion. Iron is an example of a multivalent metal. It can form an ion with a +2 charge (Fe2+) or an ion
with a +3 charge (Fe3+). When naming compounds containing a multivalent metal, Roman numerals
are used to identify the charge.
For example, nickel (III) has a charge of +3.
When nickel (III) phosphide forms, the nickel atom loses 3 electrons and the phosphorus atom gains
3 electrons. Only one of each ion is needed as the charges add up to zero. The formula is
NiP. Notice that when writing the formula, the Roman numeral is not included. It is included in the
name of the compound.
Complete the following table. The first one is done for you.
Metal
Nonmetal
Iron (III)
Iron (II)
Manganese (II)
Manganese (II)
Lead (II)
Lead (II)
Copper (I)
Copper (II)
Chromium (II)
Chromium (III)
Chromium (II)
Chromium (III)
Chromium (II)
Chromium (III)
oxygen
oxygen
chlorine
sulfur
oxygen
iodine
oxygen
chlorine
phosphorus
phosphorus
fluorine
fluorine
sulfur
sulfur
Cation
Charge
Fe3+
Anion Formula of the
Charge Compound
O2Fe2O3
Name of the Compound
Iron (III) oxide
Some ions are made of more than one atom bonded together. They are called polyatomic ions. The
formula for a polyatomic ion looks much like the formula for a compound with one important
difference. While compounds are always neutral, polyatomic ions have a charge.
For example: CO2 is the compound carbon dioxide
CO32- is the polyatomic ion carbonate. It is made of 4 atoms bonded together with 2
more electrons in total than protons.
Oppositely charged ions are attracted to each other. The metal calcium and polyatomic ion
carbonate form the ionic compound calcium carbonate. Do not change the ending of the polyatomic
ion when naming a compound containing a polyatomic ion.
Ca2+
+
CO32-  calcium carbonate
If a compound contains more than one polyatomic ion, parentheses are used. The formula for the
polyatomic ion goes inside the parentheses. The number of the polyatomic ions needed goes outside
the parenthesis.
Ca2+
+ NO2- 
Ca(NO2)2
NO2 is the nitrite ion. Two nitrite ions are needed to balance
the charge of the calcium ion.
The name of the compound is calcium nitrite.
Al3+
+ SO42- 
Al2(SO4)3
Three sulfate ions balance two aluminum ions.
The name of the ion is aluminum sulfate.
Use the table of ion to find the charge and name of the polyatomic ions. You do not need to
memorize this table!
Fill in the following table. The first one is done for you.
Cation
Al3+
Al3+
Na+
Li+
Mg2+
Mg2+
Li
Ca2+
Na
Anion name and
formula
CO32NO3CO32OHOHPO43PO43NO3NO3-
Chemical Formula
Al2(CO3)3
Name of the
Compound
Aluminum carbonate