An anion is a negatively charged ion. It is formed when an atom or a group of atoms gains one or more electrons. Since electrons carry a negative charge, gaining them makes the atom’s total negative charge greater than its positive charge. This imbalance gives it an overall negative charge.
For example, non-metal atoms like chlorine, oxygen, or sulfur often form anions. When chlorine gains an extra electron, it becomes a chloride ion with a negative charge. Anions are commonly found in salts and other compounds, where they combine with positively charged ions (cations) to form stable structures.