Halogeenin

Halogens are a group of nonmetal elements in the periodic table known as the halogen family. They occupy group 17 and include fluorine, chlorine, bromine, iodine, astatine, and the synthetic tennessine. Halogens are highly reactive and have high electronegativity, tending to gain electrons to form halide ions in compounds. They are typically diatomic in their elemental state (F2, Cl2, Br2, I2), while astatine and especially tennessine exist only in extremely limited, short-lived forms under laboratory conditions.

At room temperature the physical states of the halogens vary: fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid. Astatine is rare and radioactive, and tennessine is a synthetic element with no stable isotopes. Their reactivity generally decreases down the group, with fluorine the strongest oxidizer and astatine the most elusive in practice.

Chemically, halogens form hydrogen halides with hydrogen (HF, HCl, HBr, HI), which are typically strong acids in water, though HF is a relatively weak acid compared with the others. They form salts with alkali and alkaline earth metals (for example, NaCl, CaF2). Halogens also form interhalogen compounds (such as ClF, BrCl) and polyhalogen species (like I3−). In many compounds, halogens exhibit oxidation states from −1 up to +7.

Occurrence and uses: halogens occur in nature mainly as halide minerals, such as rock salt (NaCl) and fluorite (CaF2). They have wide applications, including chlorine for disinfection and chemical manufacturing, fluorinated polymers, bromine in flame retardants, and iodine in nutrition and medicine. Safety considerations are important, as elemental halogens and many halogen compounds are toxic or corrosive.