What term describes atoms of the same element that have different masses due to varying numbers of neutrons?

Atoms of the same element that have different masses because they contain different numbers of neutrons are known as isotopes. Each isotope has the same number of protons (which defines the element) but varies in the number of neutrons, resulting in a difference in atomic mass. For example, carbon has several isotopes, including carbon-12 (with 6 neutrons) and carbon-14 (with 8 neutrons). This variation is important in various fields such as chemistry, biology, and geology, especially in applications like radiocarbon dating.

The other terms listed do not accurately describe this concept. Molecules refer to two or more atoms bonded together, compounds are substances formed when two or more different elements combine, and ions are charged particles that either have lost or gained electrons. Each of these terms pertains to different aspects of atomic structure and chemical behavior, making isotopes the correct choice for this question.