2007 Schools Wikipedia Selection. Related subjects: Chemical elements

101 fermiummendeleviumnobelium


Periodic Table - Extended Periodic Table
Name, Symbol, Number mendelevium, Md, 101
Chemical series actinides
Group, Period, Block n/a, 7, f
Appearance unknown, probably silvery
white or metallic gray
Atomic mass (258) g/mol
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
Electronegativity 1.3 (Pauling scale)
Ionization energies 1st: 635 kJ/mol
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

Mendelevium ( IPA: /ˌmɛndəˈlɛviəm/), also known as unnilunium ( IPA: /ˌjuːniˈluːniəm/, symbol Unu) is a synthetic element in the periodic table 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.


Mendelevium (for Dmitri Mendeleyev, surname commonly spelt as Mendeleev, 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. 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 synthesized one-atom-at-a-time). Element 101 was the ninth transuranic element synthesized.


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-lifes that are less than 97 minutes, and the majority of these have half-lifes 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 amu (245Md) to 260.104 amu (260Md).

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