2008/9 Schools Wikipedia Selection. Related subjects: Chemical elements
|Name, Symbol, Number||mendelevium, Md, 101|
|Group, Period, Block||n/a, 7, f|
|Appearance||unknown, probably silvery
white or metallic gray
|Standard atomic weight||(258) g·mol−1|
|Electron configuration||[Rn] 5f13 7s2|
|Electrons per shell||2, 8, 18, 32, 31, 8, 2|
|Melting point||1100 K
(827 ° C, 1521 ° F)
|Oxidation states||2, 3|
|Electronegativity||1.3 (Pauling scale)|
|Ionization energies||1st: 635 kJ/mol|
|Magnetic ordering||no data|
|CAS registry number||7440-11-1|
Mendelevium (pronounced /ˌmɛndəˈlɛviəm/)) is a synthetic element with the symbol Md (formerly Mv) and the atomic number 101. A metallic radioactive transuranic element of the actinides, mendelevium is synthesized by bombarding einsteinium with alpha particles and was named after Dmitri Mendeleev.
Researchers have shown that mendelevium has a moderately stable dipositive (II) oxidation state in addition to the more characteristic (for actinide elements) tripositive (III) oxidation state. 256Md has been used to find out some of the chemical properties of this element while in an aqueous solution. There are no other uses of mendelevium and only trace amounts of the element have ever been produced.
Mendelevium (for Dmitri Mendeleev, surname commonly spelt as Mendeleev, Mendeleyev, Mendeléef, or even Mendelejeff, and first name sometimes spelt as Dmitry or Dmitriy) was first synthesized by Albert Ghiorso (team leader), Glenn T. Seaborg, Bernard Harvey, Greg Choppin, and Stanley G. Thompson in early 1955 at the University of California, Berkeley. The team produced 256Md ( half-life of 76 minutes) when they bombarded an 253Es target with alpha particles (helium nuclei) in the Berkeley Radiation Laboratory's 60-inch cyclotron (256Md was the first element to be synthesized one-atom-at-a-time). Element 101 was the ninth transuranic element synthesized. Contrary to some descriptions, it was never known as "unnilunium".
15 radioisotopes of mendelevium have been characterized, with the most stable being 258Md with a half-life of 51.5 days, 260Md with a half-life of 31.8 days, and 257Md with a half-life of 5.52 hours. All of the remaining radioactive isotopes have half-lives that are less than 97 minutes, and the majority of these have half-lives that are less than 5 minutes. This element also has 1 meta state, 258mMd (t½ 57 minutes). The isotopes of mendelevium range in atomic weight from 245.091 u (245Md) to 260.104 u (260Md).