Overview

Mendelevium was first made in 1955 at Berkeley by Albert Ghiorso, Glenn Seaborg and colleagues, in a remarkable experiment that identified the new element from just seventeen atoms produced one at a time by bombarding einsteinium with alpha particles. It was named after Dmitri Mendeleev, the Russian chemist who created the periodic table. Mendelevium is an intensely radioactive synthetic metal, studied only atom by atom. Its most stable isotope lasts up to about two months and it is made only a few atoms at a time, yet enough has been studied to show that, unusually, it favours a more stable low oxidation state than its neighbours, a small chemical surprise wrung from single atoms.

The target for that landmark 1955 experiment was a barely visible speck of einsteinium, itself newly available only because of the Ivy Mike fallout analysis, electroplated onto a thin gold foil and bombarded for hours; the seventeen resulting mendelevium atoms were identified individually as they decayed, a technique so sensitive it could register a single new atom of matter, a milestone that validated the entire chain of heavy-element production techniques Berkeley had built up over the preceding decade. That same recoil-and-detect method, refined further, became the standard approach used to identify every heavier element discovered since.