Cations
Home Up Cations Anions Polyatomic Ions

 

Cations

Charges and Names

First let's look at the metals, which are more likely to lose electrons than gain them.

All of the elements in Group I-A have one electron in their outermost energy level. All of these elements can lose that one valence electron. These atoms become cations with a positive one charge. 

Elements in Group II-A have two electrons in their outermost energy level. So, when these elements lose electrons, they lose two electrons and take on a positive two charge. 

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

Now for some problems. The transition metals and the metals to the right of them generally form more than one ion. We call these elements multivalent. The charges on their ions are not always predictable, although some patterns do exist. Consequently, you won't be expected to predict these, although you will be expected to work with them.

Two of these transition elements are important enough and common enough that you should memorize the charges on their ions.  They are iron and copper. Iron forms the 2+ ion and the 3+ ion. Copper forms 2+ ion and 1+ ion. 
Cations to remember
Fe3+
iron(III) ion
Cu2+
copper(II) ion
Fe2+
iron(II) ion
Cu+
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. 
Zn2+ zinc ion
Ag+ silver ion
Sc3+ scandium ion

 

To the right of the transition metals we have group III-a. Boron is not a metal so we need not consider it now. Aluminum is a metal and has three valence electrons. It can lose those three valence electrons to form an ion with a positive three charge. It is called aluminum ion. So does gallium, usually. However, because of the influence of the d electrons, sometimes gallium will lose only one electron and form an ion with a positive one charge. In that regard, gallium and the other metals below and to the right of it can be treated somewhat like transition metals. Portion of periodic table showing group 3a metals.

 

A reminder, when working with ions you should learn the charges of the copper ions and iron ions and the 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, although sometimes that information might be provided to you or you might be able to figure it out.

 

Practice with "Predicting" Charges on Cations

To give you some practice determining the charges of cations, work on these examples (also shown in exercise 6 in your workbook). Then check your answers on the next page or with the instructor.

Metal Single-ion or
Multiple-ion
Ion
Formula(s)
Na    
Ba    
Fe    
Mg    
Al    
Cu    
Ag    

 

Answers

 

Metal Single-ion or
Multiple-ion
Ion
Formula(s)
Na S Na+
Ba S Ba2+
Fe M Fe2+
Fe3+
Mg S Mg2+
Al S Al3+
Cu M Cu+
Cu2+
Ag S Ag+

 

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E-mail instructor: Eden Francis

Clackamas Community College
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