Here's why:

* Isotopes are atoms of the same element that have the same number of protons (atomic number) but a different number of neutrons. This difference in neutrons affects the atomic mass.

* Every element on the periodic table has at least two isotopes. Some elements have dozens of isotopes, though many of these are unstable and radioactive.

Example:

* Carbon has two common isotopes:

* Carbon-12 (6 protons, 6 neutrons)

* Carbon-14 (6 protons, 8 neutrons)

Important Note: While all elements have isotopes, not all isotopes are naturally occurring. Some are created in labs or through nuclear reactions.