alkuainehalogenit

Alkuainehalogenit, often simply called halogeenit, are a group of six chemical elements in the periodic table. These elements are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). They are all nonmetals and share similar chemical properties. The term "halogen" comes from Greek and means "salt-former," reflecting their tendency to form salts when they react with metals.

Halogens are highly reactive elements, especially fluorine, which is the most electronegative element. Their reactivity stems from having seven electrons in their outermost electron shell, meaning they need only one more electron to achieve a stable, filled outer shell. This makes them eager to gain an electron from other atoms, often leading to the formation of ionic bonds. In their elemental form, halogens exist as diatomic molecules, such as F₂, Cl₂, Br₂, and I₂. At room temperature, chlorine and fluorine are gases, bromine is a liquid, and iodine is a solid. Astatine is a rare, radioactive element, and tennessine is a synthetically produced, highly unstable element.

Halogen compounds have numerous applications. For instance, sodium chloride (table salt) is a fundamental compound. Chlorine is used in water purification and as a disinfectant. Fluorine compounds are found in toothpaste to prevent cavities and in refrigerants. Bromine is used in flame retardants and photographic chemicals. Iodine is essential for thyroid hormone production in humans and is used as an antiseptic.