Final answer:
An ion is an atom that has gained or lost electrons, resulting in a net charge. Positively charged ions are called cations, while negatively charged ions are called anions.
Step-by-step explanation:
An ion is an atom that has gained or lost electrons, resulting in an unequal number of protons and electrons, giving it a net charge. When an atom gains electrons, it becomes a negatively charged anion.
For example, chlorine gains one electron to become a chloride ion with a -1 charge. Conversely, when an atom loses electrons, it becomes a positively charged cation. An example is a sodium atom that loses one electron to form a sodium cation with a 1+ charge.