What are isotopes?

Isotopes are defined as atoms of the same element that have the same number of protons but different numbers of neutrons. This results in different mass numbers for isotopes of the same element while keeping the chemical properties largely similar because the number of protons (which determines the element and its chemical behavior) remains constant. For instance, carbon has isotopes such as carbon-12, which has 6 neutrons, and carbon-14, which has 8 neutrons. This variation in neutrons leads to differences in their atomic mass but does not affect their status as carbon atoms.

Other definitions do not accurately capture the essence of isotopes. Atoms with different atomic numbers belong to different elements entirely, and those that have lost electrons refer to ions, which is a different concept altogether. Finally, atoms with the same number of neutrons would not be sufficient to define isotopes either, since it is the variation in neutrons while maintaining an identical proton number that characterizes isotopes.