An anion is an ion with a net negative charge, formed when an atom or group of atoms gains one or more electrons. Anions are attracted to the positive electrode (the anode) during electrolysis, and they pair with cations in ionic compounds. The chloride ion Cl⁻ is a common anion; it contrasts with a cation, which is positively charged.

阴离子是带净负电荷的离子,在原子或原子团得到一个或多个电子时形成。电解时阴离子被吸引到正极(阳极),并在离子化合物中与阳离子配对。氯离子 Cl⁻ 是常见的阴离子;它与带正电荷的阳离子相对。