A Level Chemistry OCR Practice Exam

An anion is defined as a negatively charged ion. This occurs when an atom gains one or more electrons, resulting in an excess of negative charge. This change in charge leads to a net negative electrical charge, which differentiates anions from cations, which are positively charged ions formed when an atom loses electrons. Understanding the characteristics of anions is crucial, especially in discussions surrounding ionic compounds, acid-base reactions, and electrochemical processes, where the behavior and interactions of charged species are fundamental.

In contrast, a positively charged ion, a neutral compound, and an uncharged particle do not meet the criteria for what defines an anion, as they either involve a loss of electrons, maintain no overall charge, or lack charge entirely. This makes the concept of anions essential for grasping the broader topics in chemistry regarding ion formation and reactivity.