What makes isotopes of an element different from each other?

Isotopes of an element are defined by their differing numbers of neutrons. While the number of protons in an atom determines which element it is and gives it its identity, isotopes exist as variations of the same element that contain the same number of protons but have different numbers of neutrons. This variation in neutron count results in different atomic masses for the isotopes.

The chemical properties primarily depend on the number and arrangement of electrons, which is not changed between isotopes of the same element. Therefore, isotopes maintain the same chemical behavior despite differences in their neutron numbers. The distinctions that arise due to varying neutron counts can lead to differences in physical properties, such as stability and radioactive behavior, but fundamentally, the definition of isotopes centers on the number of neutrons.