Chemical Fact Sheet


Chemical Abstract Number (CAS #) 7440-11-1
Analytical Methods 200.8 - 6020

Synopsis from the CRC Handbook of Chemistry and Physics 92nd Edition 2011-2013

Mendelevium (Dmitri Mendeleev [18341907]), Md; at. wt. (258); at. no. 101; m.p. 827 C; valence +2, +3. Mendelevium, the ninth transuranium element of the actinide series to be discovered, was first identified by Ghiorso, Harvey, Choppin, Thompson, and Seaborg early in 1955 as a result of the bombardment of the isotope 253Es with helium ions in the Berkeley 60-inch cyclotron. The isotope produced was 256Md, which has a half-life of 78 min. This first identification was notable in that 256Md was synthesized on a one-atom-at-a-time basis. Nineteen isotopes and isomers are now recognized. 258Md has a half-life of 51.5 days. This isotope has been produced by the bombardment of an isotope of einsteinium with ions of helium. It now appears possible that eventually enough 258Md can be made so that some of its physical properties can be determined. 256Md has been used to elucidate some of the chemical properties of mendelevium in aqueous solution. Experiments seem to show that the element possesses a moderately stable dipositive (II) oxidation state in addition to the tripositive (III) oxidation state, which is characteristic of actinide elements.

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