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6.12: Halogens

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  • You've probably seen halogen lights before. You may even have halogen lights in your home. If you do, you may have noticed that they get really hot and give off a lot of light for their size. A halogen light differs from a regular incandescent light bulb, as it has a small amount of halogen gas inside the bulb. The gas combines chemically with the metal in the filament, and this extends the life of the filament. It allows the lamp to get hotter and give off more light than a regular incandescent light without burning out quickly. What is halogen gas, and which elements are halogens? This section will cover the halogens.

    Meet the Halogens

    Halogens are highly reactive nonmetallic elements in group 17 of the periodic table. As you can see in the periodic table shown in the figure below, the halogens include the elements fluorine \(\left( \ce{F} \right)\), chlorine \(\left( \ce{Cl} \right)\), bromine \(\left( \ce{Cl} \right)\), iodine \(\left( \ce{I} \right)\), and astatine \(\left( \ce{At} \right)\). All of them are relatively common on Earth except for astatine. Astatine is radioactive and rapidly decays to other, more stable elements. As a result, it is one of the least common elements on Earth.

    Figure \(\PageIndex{1}\): Halogens reside in group 17 of the periodic table, in this case the green column on the right side of the table.

    Chemical Properties of Halogens

    The halogens are among the most reactive of all elements, although reactivity declines from the top to the bottom of the halogen group. Because all halogens have seven valence electrons, they are "eager" to gain one more electron. Doing so gives them a full outer energy level, which is the most stable arrangement of electrons. Halogens often combine with alkali metals in group 1 of the periodic table. Alkali metals have just one valence electron, which they are equally "eager" to donate. Reactions involving halogens, especially halogens near the top of the group, may be explosive.

    Physical Properties of Halogens

    The halogen group is quite diverse. It includes elements that occur in three different states of matter at room temperature. Fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids. Halogens also vary in color, as you can see in the figure below. Fluorine and chlorine are green, bromine is red, and iodine and astatine are nearly black. Like other nonmetals, halogens cannot conduct electricity or heat. Compared with most other elements, halogens have relatively low melting and boiling points.

    Figure \(\PageIndex{2}\): Elemental chlorine, bromine, and iodine.

    Uses of Halogens

    Most halogens have a variety of important uses. A few are described in the table below.


    • Halogens are highly reactive nonmetal elements in group 17 of the periodic table.
    • Halogens include solids, liquids, and gases at room temperature, and they vary in color.
    • Halogens are among the most reactive of all elements. They have seven valence electrons, so they are very "eager" to gain one electron to have a full outer energy level.
    • Halogens have a variety of important uses, such as preventing tooth decay and killing germs.

    Explore More

    The table below gives the melting and boiling points of halogens. Create a graph with the data, and then describe in words the trends that you see in your graph.

    Contributors and Attributions

    • CK-12 Foundation by Sharon Bewick, Richard Parsons, Therese Forsythe, Shonna Robinson, and Jean Dupon.

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