Group 17

Group 17 is one of the columns (groups) of the periodic table of chemical elements. The elements in this group are commonly called halogens. They include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The extremely heavy synthetic element tennessine (Ts) is also placed in this group, but it is a synthetic element with extremely short-lived isotopes.

These elements behave similarly because of the electron configuration of their outer shells: each has seven electrons in its outermost (valence) level. For this reason they tend to gain one electron in order to reach a stable state, making this group highly reactive.

General properties

Moving down the group, atomic radius and density increase, while the ability to attract electrons (electronegativity) decreases. Fluorine is the most electronegative element known. The physical state at room temperature varies: fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid.

Reactivity and compounds

Halogens readily combine with metals, forming compounds called halides, such as sodium chloride (common salt). They also react with hydrogen to form gases like hydrogen chloride, which dissolves in water to form an acid. Molecules of these elements typically consist of two atoms (F₂, Cl₂, Br₂, I₂).

Applications

Chlorine is used for water purification and in chemical industries. Fluorine and its compounds are used in dental care and in some polymer materials. Iodine is necessary for thyroid health and is added to salt in many countries. Bromine has been used in flame-retardant substances.