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Chemistry LibreTexts

3.6: Ions of Some Common Elements

  • Page ID
    258846
  • Learning Objectives

    • Use the periodic table to predict ion charges.

    In many cases, elements that belong to the same group (vertical column) on the periodic table form ions with the same charge because they have the same number of valence electrons. Thus, the periodic table becomes a tool for remembering the charges on many ions. For example, all ions made from alkali metals, the first column on the periodic table, have a 1+ charge. Ions made from alkaline earth metals, the second group on the periodic table, have a 2+ charge. On the other side of the periodic table, the next-to-last column, the halogens, form ions having a 1− charge. Figure \(\PageIndex{1}\) shows how the charge on many ions can be predicted by the location of an element on the periodic table.

    Note: for a multiply-charged ion, the correct convention is to write the charge number first followed by the sign. For example, the barium cation is written Ba2+, not Ba+2.

    clipboard_e988884a4b98888686a6a6ca4d23ed94b.png

    Figure \(\PageIndex{1}\): Common ions formed by specific elements on the periodic table. The charge that a representative (main group element) acquires when it becomes an ion is related to the location on the periodic table. Note that some metal atoms, specifically the transition elements, commonly form ions with variable charges.

    Some elements, especially transition metals, can form ions with variable charges. Figure \(\PageIndex{1}\) shows the characteristic charges for some of these ions. Notice that there is no simple pattern for transition metal ions (or for the larger main group elements) as there is with the main group ions.

     

    Example \(\PageIndex{1}\)

    Which of these ions is not likely to form?

    1. Mg+
    2.  K+

    Solution

    (a) Mg is in Group 2A and has two valence electrons. It achieves octet by losing two electrons to form Mg2+ cation. Losing only one electron to form Mg+ does not make an octet, hence, Mg+ is not likely to form.

    Exercise \(\PageIndex{2}\)

    Which of these ions is not likely to form?

    1. S3
    2. N3
    Answer

    (a) S is in Group 6A and has six valence electrons. It achieves octet by gaining two electrons to form S2 anion. Gaining three electrons to form S3does not make it octet, hence, S3 is not likely to form.

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