Anion

Definition

An anion is a negatively charged ion formed when an atom gains one or more electrons. Anions are typically larger than their parent atoms due to the added electrons.

5 Must Know Facts For Your Next Test

1. Anions are formed by the gain of electrons.
2. Anions are attracted to the anode (positive electrode) in electrolysis.
3. Common examples of anions include Cl⁻, O²⁻, and SO₄²⁻.
4. Nonmetals tend to form anions because they have higher electronegativity.
5. The ionic radius of an anion is larger than its atomic radius.

Review Questions

• What happens to the size of an atom when it becomes an anion?
• Name two common elements that form anions.
• Why do nonmetals often form anions?

Related terms

Cation: A positively charged ion formed when an atom loses one or more electrons.

Ion: An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.

Electronegativity: A measure of the tendency of an atom to attract a bonding pair of electrons.