This bar chart shows the number of stable isotopes for each element. Some elements have many stable forms, while 21 elements have none at all.

Tin leads with 10 stable isotopes, owing to its "magic number" of 50 protons creating nuclear stability. Elements with even atomic numbers generally have more stable isotopes than odd-numbered neighbors - a consequence of nuclear pairing energy. Notably, technetium (Z=43) and promethium (Z=61) have no stable isotopes despite their relatively low atomic numbers.