In this example, we’ll show you how to write the formula for an ionic compound with a multivalent metal.
Ionic Compounds
With Multivalent Metals
Example 1
A multivalent metal is a metal which can form more than one ion. Each ion it forms has a different positive charge.
Multivalent Metal - A metal which can form more than one ion, each with a different charge
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.
Multivalent Metals
In this example, we’re asked to write the formula for the compound copper (II) chloride.
+2 –2
CuCl2
Cl–
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.
The periodic table tells us that copper can form either a positive 2 ion or a positive 1 ion.
Cu2+ Cl–
+2 –2
CuCl2
Cl–
Write the formula for the compound copper(II) chloride.
How do we know what the charge will be on the ion??
Cu2+ Cl–
+2 –2
CuCl2
Cl–
Write the formula for the compound copper(II) chloride.
?
Names of compounds with multivalent metals always have a roman numeral in brackets right after the name of the metal.
Cu2+ Cl–
+2 –2
CuCl2
Cl–
Write the formula for the compound copper(II) chloride.
?roman numeral-means the charge on the ion
The roman numeral simply means the charge on the ion that is used in the compound.
Cu2+ Cl–
+2 –2
CuCl2
Cl–
Write the formula for the compound copper(II) chloride.
?roman numeral-means the charge on the ion
So a roman numeral of 2 tells us the copper ion that’s used has a charge of positive 2.
Cu2+ Cl–
+2 –2
CuCl2
Cl–
Write the formula for the compound copper(II) chloride.
?
So the copper ion in this compound is Cu 2 plus
Cu2+ Cl–
+2 –2
CuCl2
Cl–
Write the formula for the compound copper(II) chloride.
The chloride ion has only one possible charge, and that is negative 1.
Cu2+ Cl–
+2 –2
CuCl2
Cl–
Write the formula for the compound copper(II) chloride.
If we have one copper II ion and one chloride ion
Cu2+ Cl–
+2 –1
CuCl2
Cl–
Write the formula for the compound copper(II) chloride.
Total Positive Charge
Total Negative Charge
The positive and negative charges are NOT balanced. They don’t add up to zero
Cu2+ Cl–
+2 –1
CuCl2
Cl–
Write the formula for the compound copper(II) chloride.
Total Positive Charge
Total Negative Charge
These DO NOT add up to zero
To make the charges balance, we add another chloride ion (click)
Cu2+ Cl–
+2 –2
CuCl2
Cl–
Write the formula for the compound copper(II) chloride.
Total Positive Charge
The total negative charge is now negative 2.
Cu2+ Cl–
+2 –2
CuCl2
Cl–
Write the formula for the compound copper(II) chloride.
Total Positive Charge
Total Negative Charge
Now the positive and negative charges are balanced. They add up to zero
Cu2+ Cl–
+2 –2
CuCl2
Cl–
Write the formula for the compound copper(II) chloride.
Total Positive Charge
Total Negative Charge
NOW these add up to zero
There is one copper ion for every two chloride ions,
Cu2+ Cl–
+2 –2Cl–
Write the formula for the compound copper(II) chloride.
So the formula is CuCl2
Cu2+ Cl–
+2 –2
CuCl2
Cl–
Write the formula for the compound copper(II) chloride.
We have now answered the question. The formula for copper (II) chloride is CuCl2.
Cu2+ Cl–
+2 –2
CuCl2
Cl–
Write the formula for the compound copper(II) chloride.
Formula:
Top Related