Mendelevium

2008/9 Schools Wikipedia Selection. Related subjects: Chemical elements

101 fermium ← mendelevium → nobelium Tm ↑ Md ↓ (Upu) Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	mendelevium, Md, 101
Chemical series	actinides
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
Physical properties
Phase	solid
Melting point	1100  K (827 ° C, 1521 ° F)
Atomic properties
Oxidation states	2, 3
Electronegativity	1.3 (Pauling scale)
Ionization energies	1st: 635 kJ/mol
Miscellaneous
Magnetic ordering	no data
CAS registry number	7440-11-1
Selected isotopes
Main article: Isotopes of mendelevium iso NA half-life DM DE ( MeV) DP 257Md syn 5.52 h ε 0.406 257Fm α 7.558 253Es SF - - 258Md syn 51.5 d ε 1.230 258Fm 260Md syn 31.8 d SF - - α 7.000 256Es ε - 260Fm β- 1.000 260No
References

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.

Notable characteristics

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.

History

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".

Isotopes

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 (t_½ 57 minutes). The isotopes of mendelevium range in atomic weight from 245.091 u (²⁴⁵Md) to 260.104 u (²⁶⁰Md).