mendelevium

Mendelevium’s chemical and physical properties are not well known because such smallamounts with short half-lives have been produced. Many of its isotopes are produced just oneatom at a time, making it difficult to weigh and measure samples. Its melting point is thoughtto be about 1,827°C, but its boiling point and density are unknown.

There are a total of 19 isotopes of mendelevium. All of them are extremelyradioactive and have half-lives ranging from 900 microseconds (for Md-245) to 51.5days (for Md-258). They are produced in very small amounts.

Named after and to honor the Russian chemist Dmitri Mendeleev who developed the periodic table of the chemical elements.

Only trace amounts of mendelevium have been artificially produced—much of it just oneatom at a time—and thus to date, only several million atoms have been artificially made. Therefore, there is not enough to measure by standard techniques. Other methods, such asion-exchange chromatography and spectroscopy, are employed to study its chemical andphysical properties.

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.

Mendelevium’s most stable isotope is Md-258, with a half-life of 51.5 days. It decays intoeinsteinium-254 through alpha (helium nuclei) decay, or it may decay through the process ofspontaneous fission to form other isotopes.

Due to the small production and dearth of knowledge about mendelevium, there are nouses for it beyond basic laboratory research.

Synthetic radioactive element produced in a cyclotron by bombarding einsteinium with alpha particles; atomic number 101, aw 256, 4 isotopes, valence = 3. Mendelevium decays by spontaneous fission with a half-life of 1.5 hr. The heaviest isotope, Md-258, has half-life of 60 days. Mendelevium is thought to have chemical properties similar to those of the rare earth thulium. It is made in research quantities only and no uses are reported.

A radioactive transuranic element of the actinoid series, not found naturally on Earth. Several short-lived isotopes have been synthesized. Symbol: Md; p.n. 101; most stable isotope ²⁵⁸Md (half-life 57 minutes).

mendelevium: Symbol Md. A radioactiv emetallic transuranic element belonging to the actinoids; a.n. 101;mass number of the first discovered nuclide 256 (half-life 1.3 hours). Several short-lived isotopes have now been synthesized. The element was first identified by Albert Ghiorso,Glenn Seaborg (1912–99), and associates in 1955.

Similar to all artificially produced radioisotopes that go through natural decay processor spontaneous fission, mendelevium is an extreme radiation hazard. There is so little of itin existence and produced annually that there is no risk of individual or public radiationpoisoning.