In this example, we’ll show you how to write the formula for an ionic compound
with a multivalent metal.
Multivalent Metal
- A metal which can form more
than one ion, each with a
different charge
A multivalent metal is a metal which can form more than one ion. Each ion it forms
has a different positive charge.
Multivalent Metals
On the periodic table you’re given, multivalent metals are the ones which have
more than one charge in the top right corner. They are shown in this diagram.
Multivalent Metals
Here, we’ve included the two horizontal rows at the bottom of the periodic table, as
many of these are multivalent.
Write the formula for the compound
copper(II) chloride.
+2
–
Cl
–2
CuCl2
In this example, we’re asked to write the formula for the compound copper (II)
chloride.
Write the formula for the compound copper(II)
chloride.
We find copper on the periodic table. It is a metal and it can form an ion with either
a positive 2 charge, or a positive 1 charge.
Write the formula for the compound copper(II)
chloride.
The element we use for chloride is chlorine. It’s ion, the chloride ion has a charge
of negative 1.
Write the formula for the compound copper(II)
chloride.
2+
Cu
+2
–
Cl
–
Cl
–2
CuCl2
The periodic table tells us that copper can form either a positive 2 ion or a positive
1 ion.
Write the formula for the compound copper(II)
chloride.
?
2+
Cu
+2
–
Cl
–
Cl
–2
CuCl2
How do we know what the charge will be on the ion??
Write the formula for the compound copper(II)
chloride.
?
2+
Cu
+2
–
Cl
roman numeral
-means the charge
on the ion
–
Cl
–2
CuCl2
Names of compounds with multivalent metals always have a roman numeral in
brackets right after the name of the metal.
Write the formula for the compound copper(II)
chloride.
?
2+
Cu
+2
–
Cl
roman numeral
-means the charge
on the ion
–
Cl
–2
CuCl2
The roman numeral simply means the charge on the ion that is used in the
compound.
Write the formula for the compound copper(II)
chloride.
?
2+
Cu
+2
–
Cl
–
Cl
–2
CuCl2
So a roman numeral of 2 tells us the copper ion that’s used has a charge of positive
2.
Write the formula for the compound copper(II)
chloride.
2+
Cu
+2
–
Cl
–
Cl
–2
CuCl2
So the copper ion in this compound is Cu 2 plus
Write the formula for the compound copper(II)
chloride.
2+
Cu
+2
–
Cl
–
Cl
–2
CuCl2
The chloride ion has only one possible charge, and that is negative 1.
Write the formula for the compound copper(II)
chloride.
2+
Cu
Total
Positive
Charge
+2
–
Cl
–
Cl
–1
CuCl2
If we have one copper II ion and one chloride ion
Total
Negative
Charge
Write the formula for the compound copper(II)
chloride.
2+
Cu
Total
Positive
Charge
+2
–
Cl
–
Cl
–1
Total
Negative
Charge
CuCl2
These DO NOT
add up to zero
The positive and negative charges are NOT balanced. They don’t add up to zero
Write the formula for the compound copper(II)
chloride.
2+
Cu
Total
Positive
Charge
+2
–
Cl
–
Cl
–2
CuCl2
To make the charges balance, we add another chloride ion (click)
Write the formula for the compound copper(II)
chloride.
2+
Cu
Total
Positive
Charge
+2
–
Cl
–
Cl
–2
CuCl2
The total negative charge is now negative 2.
Total
Negative
Charge
Write the formula for the compound copper(II)
chloride.
2+
Cu
Total
Positive
Charge
+2
–
Cl
–
Cl
–2
Total
Negative
Charge
CuCl2
NOW these add
up to zero
Now the positive and negative charges are balanced. They add up to zero
Write the formula for the compound copper(II)
chloride.
2+
Cu
+2
–
Cl
–
Cl
–2
There is one copper ion for every two chloride ions,
Write the formula for the compound copper(II)
chloride.
2+
Cu
+2
–
Cl
–
Cl
–2
CuCl2
So the formula is CuCl2
Write the formula for the compound copper(II)
chloride.
2+
Cu
+2
–
Cl
–
Cl
–2
Formula: CuCl2
We have now answered the question. The formula for copper (II) chloride is CuCl2.
Write the formula for the compound copper(II)
chloride.
2+
Cu
+2
–
Cl
–
Cl
–2
Formula: CuCl2
No
charges!
No roman
numerals!
Notice that the final formula has no charges and no roman numerals in it. In simple
ionic compounds, roman numerals are used only in names, not in formulas.