What defines isotopes of an element?

Isotopes of an element are defined by the presence of the same number of protons but a varying number of neutrons in their atomic nucleus. This difference in neutron count results in different atomic masses for the isotopes of that element, while the chemical properties remain largely the same due to the identical proton count.

For example, carbon has several isotopes, such as carbon-12 and carbon-14, both of which have six protons. The distinction comes from the number of neutrons — carbon-12 has six neutrons, while carbon-14 has eight. Thus, the key characteristic of isotopes is indeed the difference in the number of neutrons while maintaining the same number of protons, which is crucial for understanding the behavior and properties of elements in various contexts.

This understanding dismisses the notion that all isotopes are radioactive, or that they are defined by equal mass, as not all isotopes exhibit radioactivity, and isotopes generally possess distinct masses due to their varying neutron counts.