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4.5.1: Ions - Differences in Electrons

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    Learning Objectives
    • Distinguish the difference between the two types of ions.
    • Describe ion formation using electron configurations.
    • Predict ionic charge.

    Ions

    As seen in prior sections, atoms contain a nucleus with neutrons and positively charged protons, surrounded by negatively charged electrons. In an atom, the total number of electrons, negative charge, equals the total number of protons, positive charge, and therefore, atoms are electrically neutral or uncharged. If an atom loses or gains electrons, it will become a positively or negatively charged particle, called an ion. The loss of one or more electrons results in more protons than electrons and an overall positively charged ion, called a cation. For example, a sodium atom with one less electron is a cation, Na+, with a +1 charge (Figure \(\PageIndex{1}\)).

    3.2.1.jpg
    Figure \(\PageIndex{1}\): On the left, a sodium atom has 11 electrons. On the right, the sodium ion only has 10 electrons and a 1+ charge.

    When an atom gains one or more electrons, it becomes a negatively charged anion, because there are more electrons than protons. When chlorine gains one electron it forms a chloride ion, Cl–, with a –1 charge (Figures \(\PageIndex{2}\))

    The names for positive and negative ions are pronounced CAT-eye-ons (cations) and ANN-eye-ons (anions), respectively.

    3.2.2.jpg
    Figure \(\PageIndex{2}\): The Formation of a Chlorine Ion. On the left, the chlorine atom has 17 electrons. On the right, the chloride ion has 18 electrons and has a 1− charge.

    Key Takeaways

    • Ions can be positively charged or negatively charged.
    • Ionic charge relates to valence electrons and valence shells.

    Exercises

    1. What are the two types of ions?

    2. When the following atoms become ions, what charges do they acquire?

    1. Li
    2. S
    3. Ca
    4. F

    4. Identify each as a cation, an anion, or neither.

    1. H+
    2. Cl−
    3. O2
    4. Ba2+
    5. CH4
    6. CS2

    5. Identify each as a cation, an anion, or neither.

    1. NH3
    2. Br−
    3. H−
    4. Hg2+
    5. CCl4
    6. SO3

    Answers

    1. Cations (positive charged) and anions (negative charged)

      1. 1+
      2. 2−
      3. 2+
      4. 1−

    4.

    1. cation
    2. anion
    3. neither
    4. cation
    5. neither
    6. neither
    5.
    1. neither
    2. anion
    3. anion
    4. cation
    5. neither
    6. neither

    Contributors

    • Lisa Sharpe Elles, University of Kansas

    4.5.1: Ions - Differences in Electrons is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by LibreTexts.