What is the term for an atom or molecule that carries a charge due to the gain or loss of an electron?

An atom or molecule that carries a charge because it has either gained or lost one or more electrons is called an ion. This charged state arises from the imbalance between the number of protons and electrons in the species. When an atom loses an electron, it becomes positively charged and is known as a cation. Conversely, when an atom gains an electron, it acquires a negative charge and is referred to as an anion.

This concept is fundamental in chemistry as ions play critical roles in various chemical reactions, electrical conductivity in solutions, and the formation of ionic bonds. Understanding ions is essential for grasping many topics in chemistry, including solutions, acids and bases, and electrochemistry.

The other terms listed—molecule, compound, and element—do not specifically describe a charged species. A molecule refers to two or more atoms bonded together, a compound is a type of molecule that consists of different elements, and an element is a pure substance that cannot be broken down into simpler substances. None of these terms inherently involve the concept of charge related to electron gain or loss. Thus, recognizing the definition of an ion is crucial for understanding the broader picture of atomic interactions in chemistry.