What defines isotopes?

Isotopes are defined as variants of a particular chemical element that have the same number of protons but different numbers of neutrons. This distinction is crucial because the number of protons in an atom defines the element itself—the atomic number. However, the differing number of neutrons results in varying atomic masses for these isotopes. For instance, carbon has isotopes like carbon-12 and carbon-14; they both have 6 protons, but carbon-12 has 6 neutrons, while carbon-14 has 8 neutrons.

This variation can influence the stability of the atom, leading to radioactivity in certain isotopes, but does not affect the chemical properties since those are primarily determined by the number of protons and the arrangement of electrons, which remain constant in isotopes of the same element.