one of two or more atoms of the same element that have the same number of protons in their nucleus but different numbers of neutrons, nuclides having the same atomic number but different mass number, ühe ja sama keem. elemendi teisendid, mille aatomituumades on ühesugune arv prootoneid, kuid erisugune arv neutroneid. I-de füüsikalis-keem. omadused on peaaegu identsed, sest need omadused olemevad p