From the CRC handbook of Chemistry and Physics, CRC Press, Cleveland, 55th ed., 1974-75 "The Elements" by C.R. Hammond. page B-6
MENDELEVIUM (Dmitri Mendeleev), Md; at. wt. (256); at. no. 101; 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 Es(253) with helium ions in the Berkeley 60-inch cyclotron. The isotope produced was Md(256), which has a half-life of 77 minutes. This first identification was notable in that Md(256) was synthesized on a one-taom-at-a-time basis. Four isotopes are now recognized. Md(258) has a half-life of two months. This isotope has been produced by the bombardment of an isotope of einsteinium with ions of helium. It now appears possible that eventually enough Md(258) can be made so that some of its physical properties can be determined. Md(256) 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 dispositive (II) oxidation state in addition to the tripositive (III) oxidation state, which is characteristic of actinide elements.
