<page_title> Isotopes of mendelevium </page_title> <section_title> List of isotopes </section_title> <table> <cell> 258Md <col_header> nuclide symbol </col_header> <col_header> excitation energy </col_header> </cell> <cell> 51.5(3) d <col_header> half-life </col_header> </cell> </table>
The longest-lived isotope is ²⁵⁸Md.