an artificial radioactive element of the actinide series; atomic number, 101. The element has no stable isotopes.
The first atoms of mendelevium were synthesized in 1955 by the American scientists A. Ghiorso, B. Harvey, G. Choppin, S. Thompson, and G. Seaborg, who irradiated nuclei of the einsteinium isotope 253Es with highly accelerated helium nuclei (Ʊ-particles). The nuclear reaction 253Es(a,n) 256Md occurred in this case. In 1962 and later, the scientists at the Joint Institute for Nuclear Research at Dubna obtained hundreds of Md atoms for chemical studies by the reaction 238U (22Ne,p 3n)256Md. In initial experiments, the American scientists produced only 17 atoms of the element. Nevertheless, it was possible to determine some of the chemical properties of the new element and to deter-mine the element’s position in the periodic table.
The element is named in honor of D. I. Mendeleev. Isotopes of Md with the mass numbers 252, 254, 255, 256, 257, and 258 are known. The most stable isotope is the a-radioactive 258Md with a half-life T1/2 of 54 days. Like other heavy actinides, Md is capable of exhibiting the oxidation state of + 3 in solution. Md may also be present in the oxidation state of + 2, and as deter-mined by Soviet scientists in 1962, in the oxidation state of + 1.