Cations
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Cations

Charges and Names

First let's look at the metals, which lose electrons to become our cations.

All of the elements in Group I-A  become cations with a positive one charge. To name these simple, predictable ions we simply use the name of the element - lithium ion, sodium ion, potassium ion, and so on.

Elements in Group II-A lose two electrons and take on a positive two charge. These simple, predictable ions are called beryllium ion, magnesium ion, calcium ion and so on.

Left portion of periodic table showing charges on group 1a and 2a metal ions.

Now we need to deal with metals that do not form simple, predictable ions. We saw in lesson 7 that the transition metals and the metals to the right of them generally form more than one ion.  That means that when we use these metals we need to indicate which ion we are using.

Each different ion needs to have its own distinct name. The modern (and somewhat simpler) way to name these kinds of ions is to put the charge or oxidation state in parentheses using Roman numerals after the name of the element. For example chromium(II) ion and chromium(III) ion. This is called the Stock name.
Cr3+ chromium(III) ion
Cr2+ chromium(II) ion

 

An older method uses an "-ic" ending for the higher charge or oxidation state and an "-ous" ending for the lower charge or oxidation state. For example, chromous ion and chromic ion.  (I like to remember it as there's an "i" in "higher" and an "o" in "lower".)
Cr3+ chromic ion
Cr2+ chromous ion

 

When the ous/ic method of naming is used, the Latin name for the element is often used in place of the modern name. The ions of iron, for example, can be called ferrous ion and ferric ion.
Fe3+ ferric ion
Fe2+ ferrous ion

 

In lesson 7 you memorized the common ions for iron and copper. Now you also need to memorize their names.  Iron forms the iron(III) ion and the iron(II) ion. The old names for these are ferric ion and ferrous ion. Copper forms copper(II) ion and copper(I) ion. The old names for these are cupric ion and cuprous ion.
Cations to remember
Fe3+ ferric ion
iron(III) ion
Cu2+ cupric ion
copper(II) ion
Fe2+ ferrous ion
iron(II) ion
Cu+ cuprous ion
copper(I) ion

 

A few of the transition elements form only one ion or oxidation state. For example zinc ion, silver ion and scandium ion. Consequently these ions do not need a Roman numeral attached to them. 
Zn2+ zinc ion
Ag+ silver ion
Sc3+ scandium ion

 

To the right of the transition metals we have metals that act like transition metals in that they tend to form more than one type of ion. In that regard, gallium and the other metals below and to the right of it must be named like transition metals with a Roman numeral or the -ic/-ous endings. Portion of periodic table showing group 3a metals.

 

A reminder, when working with ions you should learn the names and charges of the copper ions and iron ions and the names and charges of any ions that can be predicted from the position of the element on the periodic table. Expect to look up the charges of other ions such as the transition elements and the metals to the right of them, and then be able to name them correctly.

 

Practice with Naming Cations

 

The common charges for ions of several of the elements are shown here (and listed in exercise 2 in your workbook). Take time now to name all of these ions using both the modern (Stock) and old names where appropriate. If the old names require using the Latin names for the elements, they are given in the exercise 2. Check your answers on the next page or with the instructor and then continue. Central portion of periodic table showing common charges for several transition metals.

 

Answers

Element Charge New name Old name
chromium +2 chromium(II) ion chromous ion
+3 chromium(III) ion chromic ion
cobalt +2 cobalt(II) ion cobaltous ion
+3 cobalt(III) ion cobaltic ion
copper +1 copper(I) ion cuprous ion
+2 copper(II) ion cupric ion
iron +2 iron(II) ion ferrous ion
+3 iron(III) ion ferric ion
lead +2 lead(II) ion plumbous ion
+4 lead(IV) ion plumbic ion
mercury +1 mercury(I) ion mercurous ion
+2 mercury(II) ion mercuric ion
nickel +2 nickel(II) ion nickelous ion
+3 nickel(III) ion nickelic ion
silver +1 silver ion silver ion
tin +2 tin(II) ion stannous ion
+4 tin(IV) ion stannic ion
zinc +2 zinc ion zinc ion

 

Practice with Naming Cations

To give you some practice determining the names of cations, work on these examples (also shown in exercise 3 in your workbook). As a review, also write the charge or charges of the ions.  Then check your answers on the next page or with the instructor.

Metal Ion
Formula(s)
Ion
Name(s)
Na    
Ba    
Fe    
Mg    
Al    
Cu    
Ag    

 

Answers

 

Metal Ion
Formula(s)
Ion
Name(s)
Na Na+ sodium ion
Ba Ba2+ barium ion
Fe Fe2+
Fe3+
iron(II) ion, ferrous ion
iron(III) ion, ferric ion
Mg Mg2+ magnesium ion
Al Al3+ aluminum ion
Cu Cu+
Cu2+
copper(I) ion, cuprous ion
copper(II) ion, cupric ion
Ag Ag+ silver ion

 

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