Isotopes Atoms having the same atomic number Z but different numbers of neutrons w are called isotopes of the element identified by Z and all elements have a number of Isotopes O.170.18O Specially, Hydrogen H, deuterium H, and tritium HIsotopes • Atoms having the same atomic number Z, but different numbers of neutrons N are called isotopes of the element identified by Z, and all elements have a number of isotopes. • 16O, 17O, 18O • Specially, Hydrogen 1H, deuterium 2H, and tritium 3H