Isotopes are variants of a particular chemical element that have the same number of protons in their atomic nuclei, but different numbers of neutrons. This results in isotopes having the same atomic number, but different atomic masses. Isotopes are important in various fields of science, including chemistry, geology, biology, and archaeology, as they can be used for purposes such as dating rocks and fossils, tracing the movement of elements through the environment, and diagnosing and treating medical conditions. Isotopes are also used in nuclear power and radiation therapy.