Halide ions are negatively charged ions formed when halogens gain an electron. The most common halide ions are chloride (Cl⁻), bromide (Br⁻), and iodide (I⁻). These ions are derived from the halogens, which are found in Group 17 of the periodic table. Halide ions play essential roles in various chemical reactions and are often found in salts, such as sodium chloride (table salt). Halide ions are important in biological systems and industrial applications. For example, chloride ions are crucial for maintaining fluid balance in the body, while bromide ions are used in some medications. Iodide ions are vital for thyroid function, as they are necessary for the production of thyroid hormones.