Atoms with the same number of protons but different numbers of neutrons are called what?

Atoms with the same number of protons but different numbers of neutrons are defined as isotopes. This means that isotopes represent variations of the same chemical element, as they share the same atomic number (number of protons) but have different mass numbers due to the differing number of neutrons.

For example, carbon has isotopes such as carbon-12 and carbon-14. In both cases, the number of protons remains six, which identifies them as carbon, but carbon-12 has six neutrons while carbon-14 has eight neutrons. This variation in neutron count results in different atomic masses and can lead to differences in stability and radioactive properties.

Other options such as ions, elements, and molecules do not fit this definition. Ions are atoms that have gained or lost electrons, resulting in a charge, while elements are pure substances made of only one type of atom. Molecules are formed when two or more atoms bond together, which may consist of different elements or isotopes. Only isotopes specifically describe the scenario of identical protons with varying neutrons.