The term given to different forms of any element that only vary in their number of neutrons is called "isotopes." Isotopes are atoms of the same element that have the same number of protons in their nucleus but different numbers of neutrons. These variations in the number of neutrons give isotopes slightly different atomic masses. To identify the term "isotopes" for such variations, you can consult scientific literature, textbooks, or online resources that specialize in chemistry.
