anion

An anion is an ion with a negative electrical charge, meaning it has more electrons than protons in its nucleus. Anions are formed by the addition of one or more electrons to a stable neutral atom. In this way, the charge of the nucleus (the number of protons) is less than the number of electrons, resulting in an overall negative charge.

An example of an anion is chloride anion (Cl⁻). Neutral chlorine atoms have 17 electrons and 17 protons, making them electrically neutral. When one electron is added, a negatively charged Cl⁻ anion with 17 protons and 18 electrons is formed.

Anions play an important role in chemical reaction and interactions. Most chemical compounds are electrically neutral, so anions usually combine with cations (positively charged ions) to form an electrically neutral substance.