Valence Electrons

Key Questions

  • Answer:

    It is not the valence electrons themselves, but the number of valence electrons that determines the chemical properties of an element.


    Elements whose atoms have the same number of valence electrons are grouped together in the Periodic Table.

    Generally, elements in Groups 1, 2, and 13 to 17 tend to react to form a closed shell with a noble gas electron configuration ending in #ns^2 np^6#.


    The most reactive metals are those from Groups 1 and 2.

    They need to lose only one or two valence electrons to form positive ions with a noble gas configuration.


    Nonmetals tend to attract additional valence electrons to form either ionic or covalent bonds.

    The most reactive nonmetals are the halogens, e.g., #"F"# and #"Cl"#.

    They have one less electron configuration than a noble gas, so they require only one additional valence electron gain an octet.

    To form an ionic bond, a halogen atom can remove an electron from another atom in order to form an anion (e.g., #"F"^"-", "Cl"^"-"#, etc.).

    To form a covalent bond, one electron from the halogen and one electron from another atom form a shared pair.

    For example, in #"H–F"#, the dash represents a shared pair of valence electrons, one from #"H"# and one from #"F"#.

  • Valence electrons are the electrons present in the outermost shell of an atom.

    You can easily determine the number of valence electrons an atom can have by looking at its Group in the periodic table.

    For example, atoms in Groups 1 and 2 have 1 and 2 valence electrons, respectively.

    Atoms in Groups 13 and 18 have 3 and 8 valence electrons, respectively.

    Valence electrons are responsible for the reactivity of an element. They determine how "willing" the elements are to bond with each other to form new compounds. If the valence shell of an element is full, such as with a noble gas, then the element does not want to gain or lose an electron.

    For example, alkali metals, which all have a valency of 1, want to lose that one electron and are likely to form ionic bonds (such as in the case of NaCl, or table salt) with a Group 17 element, which has a valency of 7 and wants to gain that one electron from the alkali metal (Group 1 element) to form a stable valency of 8.

    For more on valence electrons and how they're related to the periodic table, I strongly recommend this video:

    Citations: Tyler Dewitt. (2012, December 18) Valence Electrons and the Periodic Table [Video File].