MENDELEVIUM

(Md), synthetic chemical element of the actinide series in Group IIIb of the periodic table, atomic number 101. It was the first element to be synthesized and discovered one atom at a time. Not occurring in nature, mendelevium (as the isotope mendelevium-256) was discovered (1955) by Albert Ghiorso, Bernard G. Harvey, Gregory R. Choppin, Stanley G. Thompson, and Glenn T. Seaborg at the University of California, Berkeley, as a product resulting from the helium-ion bombardment of a minute quantity (1,000,000,000 atoms) of einsteinium-253 (atomic number 99). In about a dozen repetitions of the experiment, the team of scientists produced 17 atoms of mendelevium, which were identified by the ion-exchange adsorptionelution method (mendelevium behaved like its rare-earth homologue thulium). Other isotopes of mendelevium, all radioactive, have been discovered. The stablest is mendelevium-258 (two-month half-life). Studied by means of radioactive tracer techniques, mendelevium exhibits a predominant +3 oxidation state, as would be expected by its position in the actinide series; a moderately stable +2 oxidation state is also known. atomic number 101 stablest isotope 258 valence 2,3 electronic config. 2-8-18-32-31-8-2 or (Rn)5f 137s2