Stable and Unstable Isotopes That's not to say that an element can't have more than one stable isotope. Ordinary hydrogen and deuterium are both stable; tin has ten stable isotopes, more than any other element. Conversely, there are some elements that don't have any stable isotopes at all. Elements 43 and 61, technetium (Tc) and promethium (Pm), were missing from Mendeleev's original periodic table for this reason. All the elements beyond bismuth (atomic number 83) are unstable as well.

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