What do we call elements whose atoms have the same number of protons but different numbers of neutrons?

Elements whose atoms have the same number of protons but different numbers of neutrons are referred to as isotopes. The defining characteristic of isotopes is that they are variations of the same element, which means they have the same atomic number (the number of protons) but differ in their mass number due to the varying number of neutrons. This difference in neutron count can lead to different physical properties while maintaining the same chemical properties as the element.

For instance, carbon has isotopes like Carbon-12 and Carbon-14, both of which have six protons but differ in the number of neutrons (six for Carbon-12 and eight for Carbon-14). This concept is crucial in various fields such as radiocarbon dating, nuclear medicine, and understanding elemental behaviors in different environments.