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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. |
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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 |
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| 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 |
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| 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. |
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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 |
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| Ba |
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| Fe |
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| Mg |
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| Al |
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| Cu |
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| Ag |
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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
©1998, 2002 Clackamas Community College, Hal Bender
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