Isotopes of mendelevium

Mendelevium (Md) is a synthetic element, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was ²⁵⁶Md (which was also the first isotope of any element produced one atom at a time) in 1955. There are 16 known radioisotopes, ranging in atomic mass from ²⁴⁵Md to ²⁶⁰Md, and 5 isomers. The longest-lived isotope is ²⁵⁸Md with a half-life of 51.3 days, and the longest-lived isomer is ^258mMd with a half-life of 58.0 minutes.