Jalogeenejä

Jalogeenejä, often referred to as halogens, comprise a group of five highly reactive nonmetal elements found in Group 17 of the periodic table. These elements are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The name "halogen" itself is derived from Greek roots meaning "salt-former," reflecting their propensity to react with metals to produce salts.

In their elemental form, halogens exist as diatomic molecules, meaning they consist of two atoms bonded together (e.g., F2, Cl2). They exhibit a gradual change in physical properties down the group. Fluorine is a pale yellow gas, chlorine a greenish-yellow gas, bromine a reddish-brown liquid, and iodine a dark purple solid that sublimes readily into a violet vapor. Astatine is a rare and highly radioactive element, and its properties are less well-characterized.

Halogens are among the most electronegative elements, meaning they have a strong tendency to attract electrons. This high electronegativity contributes to their vigorous reactivity, particularly with metals. They readily form ionic compounds by accepting an electron from a metal atom. In reactions with nonmetals, they can form covalent compounds by sharing electrons.

Fluorine is the most reactive halogen and a powerful oxidizing agent. Chlorine is widely used as a disinfectant for water and in the production of plastics and solvents. Bromine finds applications in flame retardants and photographic chemicals. Iodine is essential for thyroid hormone production in humans and is used as an antiseptic. Astatine's radioactivity limits its practical applications, though it is studied for potential use in targeted cancer therapy.