What characterizes an anion?

An anion is characterized by an atom that has gained electrons, resulting in a net negative charge. Atoms normally have an equal number of protons and electrons, which balances their positive and negative charges. When an atom gains one or more electrons, it increases the number of negative charges compared to positive charges, thereby giving the atom an overall negative charge.

This definition aligns with the basic principles of atomic structure and ionic charge. For example, when a chlorine atom gains an electron, it becomes a chloride ion (Cl⁻), which is an anion. The increase in the number of electrons compared to protons is what leads to the anion's negative charge, distinguishing it from cations, which are positively charged ions formed when an atom loses electrons.