Stable Isotope - Isotopes Per Element

Isotopes Per Element

Of the known chemical elements, 80 elements have at least one stable nuclide. These comprise the first 82 elements from hydrogen to lead, with the two exceptions, technetium (element 43) and promethium (element 61), that do not have any stable nuclides. As of December 2011, there were a total of 254 known "stable" nuclides. In this definition, "stable" means a nuclide that has either never been observed to decay against the natural background. Thus, these elements have half lives too long to be measured by any means, direct or indirect.

Stable isotopes:

• one element (tin) has ten stable isotopes
• one element (xenon) has eight stable isotopes
• four elements have seven stable isotopes apiece
• eight elements have six stable isotopes apiece
• ten elements have five stable isotopes apiece
• nine elements have four stable isotopes apiece
• five elements have three stable isotopes apiece
• 16 elements have two stable isotopes apiece
• 26 elements have one single stable isotope.

These last 26 are thus called monoisotopic elements. The mean number of stable isotopes for elements which have at least one stable isotope is 254/80 = 3.2.