Mendelevium Md

Discovery

In 1955 Albert Ghiorso, Bernard Harvey, Gregory Choppin, Stanley Thompson and Glenn Seaborg at the University of California, Berkeley, went after element 101. The target material, einsteinium-253, was painfully scarce: irradiating plutonium in a reactor for about a year yielded only around a billion atoms. Calculations suggested each experiment would produce roughly one atom of the new element.

The team devised an ingenious workaround. When alpha particles struck the einsteinium, any newly formed atoms recoiled out of the target and were caught on a thin gold foil placed just in front of it. That meant the precious target could be reused, while the foil could be dissolved quickly for chemical separation. The new atoms were recognised through the spontaneous fission of the fermium they decayed into. Over a series of runs the team identified 17 atoms in all.

The first isotope, mendelevium-256, has a half-life of about 78 minutes. The experiment was the first synthesis and identification of an element atom by atom, a technique that became standard for all heavier elements.

Origin of the name

The name honours Dmitri Mendeleev, who organised the periodic table and predicted the properties of undiscovered elements. Naming an element after a Russian scientist at the height of the Cold War was a bold gesture, and Seaborg later recalled seeking the US government's permission. IUPAC approved the name in 1955 with the symbol Mv, then changed the symbol to Md in 1957.

Main uses

• Basic research: Only a few atoms up to a few million can be produced at a time, so mendelevium has no practical use. Chemical studies show that +3 is its most stable state in solution but that +2 is also fairly accessible, illustrating how the +2 state gains importance toward the end of the actinide series.
• Advances in technique: The recoil-catching and rapid ion-exchange methods refined for mendelevium became essential tools in the hunt for element 102 and beyond.

Isotopes

Mendelevium has no stable isotopes. The longest-lived is mendelevium-258, with a half-life of about 51.5 days. Mendelevium-256, the first isotope made, has a half-life of about 78 minutes and decays mostly by electron capture into fermium-256. Research typically relies on the easier-to-produce mendelevium-256 and the longer-lived mendelevium-258.

In everyday life

Mendelevium does not occur in nature and has no connection with daily life. It has never been gathered in weighable quantities, and the metal has never been isolated. Although it is radioactive, the amounts in existence are so tiny that any real exposure risk is confined to specialised laboratories.