Isotopes are identified by their mass. This property, also known as atomic mass, is the total number of protons and neutrons contained in the isotope.
Isotopes are atoms containing the same number of protons and electrons. Each element can have multiple isotopes, which are identified by the number of neucleons. For example, hydrogen has three isotopes: protium, deuterium and tritium. Each isotope has the same number of protons and electrons but different numbers of neutrons. Isotopes are also identified as stable or unstable. Unstable isotopes eventually decay and turn into another isotope or element. This process of decay is known as radiation.