5.3: Valence Electrons and the Periodic Table

CHEM 1020 Introductory Chemistry · LibreTexts

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    Interactive periodic table of the elements, in pictures and words

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    Learning Objectives
    • Define valence electrons.
    • Describe how the number of valence electrons are related the arrangement of the main group elements and its chemical behavior.

    Family Features: Outer Electron Configurations

    Valence Electrons

    The valence shell is the outermost shell of an atom in its uncombined state, which contains the electrons most likely to account for the nature of any reactions involving the atom and of the bonding interactions it has with other atoms. Valence electrons are the outer-shell electrons of an atom. These are electrons that can participate in the formation of a chemical bond. The presence of valence electrons can determine the element's chemical properties and whether it may bond with other elements.

    An atom with a closed shell of valence electrons tends to be chemically inert. An atom with one or two valence electrons more than a closed shell is highly reactive, because the extra valence electrons are easily removed to form a positive ion. An atom with one or two valence electrons fewer than a closed shell is also highly reactive, because of a tendency either to gain the missing valence electrons (thereby forming a negative ion), or to share valence electrons (thereby forming a covalent bond).

    The number of valence electrons of an element can be determined by the periodic table group (vertical column) in which the element is categorized (Table \(\PageIndex{1}\)). With the exception of groups 3–12 (the transition metals), the units digit of the group number identifies how many valence electrons are associated with a neutral atom of an element listed under that particular column.

    Table \(\PageIndex{1}\): Number of Valence Electrons for Main Periodic Table Groups.
    Periodic table group Valence electrons
    Group 1 (I) (alkali metals) 1
    Group 2 (II) (alkaline earth metals) 2
    Groups 3-12 (transition metals) 2*
    Group 13 (III) (boron group) 3
    Group 14 (IV) (carbon group) 4
    Group 15 (V) (pnictogens) 5
    Group 16 (VI) (chalcogens) 6
    Group 17 (VII) (halogens) 7
    Group 18 (VIII or 0) (noble gases) 8**

    * The general method for counting valence electrons is generally not useful for transition metals.

    ** Except for helium, which has only two valence electrons.

    Valence Electrons and the Periodic Table

    Video \(\PageIndex{1}\) Finding the valence electron for an element.

    Summary

    • Valence electrons are the outer-shell electrons of an atom. These are electrons that can participate in the formation of a chemical bond.

    References

    1. Petrucci, Ralph H., William S. Harwood, F. G. Herring, and Jeffrey D. Madura. General Chemistry: Principles and Modern Applications. 9th ed. Upper Saddle River: Pearson Education, Inc., 2007.
    2. Sisler, Harry H. Electronic structure, properties, and the periodic law. New york; Reinhold publishing corporation, 1963.
    3. Petrucci, Ralph H., Carey Bissonnette, F. G. Herring, and Jeffrey D. Madura. General Chemistry: Principles and Modern Applications. Custom Edition for CHEM 2. Pearson Learning Solutions, 2010.

    Contributors and Attributions

    5.3: Valence Electrons and the Periodic Table is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.