The periodic table organizes chemical elements by atomic number, with vertical columns (groups) containing elements that share similar chemical properties due to their outer electron configuration. Group 17, located to the left of the noble gases, is a distinct family of nonmetallic elements known as halogens. This name, meaning “salt-forming,” reflects their tendency to react with metals to create salt compounds.
The Halogen Elements
Group 17 encompasses six elements: Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At), and Tennessine (Ts). Fluorine is a pale yellow gas. Chlorine is a light green gas known for its reactivity. Bromine is a reddish-brown liquid with a strong, disagreeable odor. Iodine is a dark grey solid that sublimes into a violet gas when heated.
Astatine (At) is a radioactive element with short-lived isotopes, chemically similar to iodine. Tennessine (Ts) is a synthetic element produced in laboratories. Both are highly unstable, radioactive, and have very limited practical applications due to their extremely short half-lives.
Defining Characteristics
The elements in Group 17 share distinct chemical and physical properties. Their high reactivity stems from having seven valence electrons, making them one electron short of a stable noble gas configuration. This leads them to readily gain an electron in chemical reactions and makes them highly electronegative; fluorine is the most electronegative element.
Their reactivity allows them to form salts with metals, which is the basis for their “halogen” name. Physical properties show a regular gradation down the group. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid. This progression reflects increasing atomic size and intermolecular forces.
Everyday Applications
Halogen elements are widely used in various everyday applications due to their unique properties. Fluorine finds use in dental health products, where it helps prevent tooth decay. It is also used in the production of refrigerants and non-stick coatings. Chlorine is extensively employed as a disinfectant for water treatment in swimming pools and municipal water supplies. It is also a key component in manufacturing polyvinyl chloride (PVC), a versatile plastic.
Bromine has applications as a flame retardant in various materials, helping to reduce flammability. It has also been historically used in photography. Iodine is recognized for its antiseptic properties and is commonly found in first-aid solutions for wound disinfection. It is also important for human health, as it is a necessary nutrient for proper thyroid function. Due to their extreme instability and radioactivity, astatine and tennessine have few, if any, practical everyday applications beyond scientific research.