DENSITY: Unknown
2+ , Md 3+

Mendelevium was discovered in 1955 by Albert Ghiorso, Bernard G. Harvey, Gregory R. Choppin, Stanley G. Thompson, and Glenn T. Seaborg via the bombardments of a minute quantity of a rare, radioactive isotope of einsteinium ( 253 Es) with α -particles in the 60-inch cyclotron of the University of California, Berkeley, which produced 256 Md. Only 17 atoms were detected. Md is the first element to be produced and chemically identified on a one-atom-at-a-time basis. Mendelevium-256 decayed by electron capture (with a 1.3-hour half-life) to the known daughter nuclide fermium-256 ( 256 Fm), which decayed primarily by spontaneous fission (with a half-life of 2.6 hours). The atoms recoiling from the target were caught in a thin gold catcher foil that was quickly dissolved, and the resulting solution was passed through a cation exchange resin column which sorbed the atoms of Md and its known daughter Fm. Es and Fm were then identified by the order of their elution from the column with alpha-hydroxyisobutyrate solution relative to the known elution positions of Es and Cf tracers.

Mendelevium is the heaviest element whose initial atomic number assignment was based on chemical separation. It was named after Dimitri Mendeleev, the great Russian chemist. Mendelevium isotopes of masses 245 through 260 have been reported. All are radioactive, decaying by α -particle emission, electron capture, and/or spontaneous fission, with half-lives ranging from 0.35 second for mass 245 to 31.8 days for mass 260, the heaviest isotope. The ground state electronic configuration of Md is believed to be [Rn]5f 13 7s 2 , by analogy to its lanthanide homologue thulium (element 69). Its most stable ion in aqueous solution is Md 3+ , although Md 2+ can be prepared with strong reducing agents . The metal is believed to be divalent because of its high volatility relative to that of other actinide metals, but this has not been experimentally verified.

SEE ALSO Actinium ; Berkelium ; Einsteinium ; Fermium ; Lawrencium ; Mendeleev, Dimitri ; Neptunium ; Nobelium ; Plutonium ; Protactinium ; Radioactivity ; Rutherfordium ; Seaborg, Glenn Theodore ; Thorium ; Transmutation ; Uranium .

Darleane C. Hoffman


Ghiorso, A.; Harvey, B. G.; Choppin, G. R.; Thompson, S. G.; Seaborg, G.T. (1955). "New Element Mendelevium, Atomic Number 101." Physical Review 98:1518–1519.

Hoffman, Darleane C.; Ghiorso, Albert; and Seaborg, Glenn T. (2000). The Transuranium People: The Inside Story. Singapore: World Scientific Publishing.

Hoffman, Darleane C., and Lee, Diana M. (1999). "Chemistry of the Heaviest Elements—One Atom at a Time." Journal of Chemical Education 76(3):331–347.

Seaborg, Glenn T., and Loveland, Walter D. (1990). The Elements beyond Uranium. New York: Wiley.

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