/ ˈaɪsətəʊp; NAmE -toʊp/ noun
( physics , chemistry ) one of two or more forms of a chemical element which have the same number of protons but a different number of neutrons in their atoms. They have different physical properties (= characteristics) but the same chemical ones :
radioactive isotopes
the many isotopes of carbon
••
WORD ORIGIN
1913: coined by F. Soddy, from iso- equal + Greek topos place (because the isotopes occupy the same place in the periodic table of elements).