Atoms of the same element can differ in their number of neutrons. This difference creates isotopes.

Here's a breakdown:

* Element: Defined by the number of protons in the nucleus.

* Isotopes: Atoms of the same element with different numbers of neutrons. This means they have the same atomic number (number of protons) but different mass numbers (number of protons + neutrons).

Example: Carbon-12 and Carbon-14 are both isotopes of carbon. They both have 6 protons, but Carbon-12 has 6 neutrons, while Carbon-14 has 8 neutrons.

Let me know if you'd like more details on isotopes or anything else related to atomic structure!