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101 fermiummendeleviumnobelium


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
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
Notable 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 (chemical symbol Md (formerly Mv), atomic number 101), also known as unnilunium (symbol Unu), is a synthetic element in the periodic table. A metallic radioactive transuranic element[1] of the actinide series, mendelevium is synthesized by bombarding einsteinium with alpha particles. Only trace amounts of the element have been produced. The element is of interest mainly for research purposes, and practical applications have yet to be developed.


Mendelevium was named after Dmitri Mendeleev (surname also spelt as Mendeleyev, Mendeléef, or even Mendelejeff; first name sometimes spelt as Dmitry or Dmitriy). It 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.

Notable characteristics

Mendelevium is an inner transition metal of the actinide series, situated in period seven of the periodic table, between fermium and nobelium. 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. Currently, there are no practical uses of mendelevium, and only trace amounts of the element have been produced.


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 five minutes. This element also has one meta state, 258mMd (t½ 57 minutes). The isotopes of mendelevium range in atomic weight from 245.091 amu (245Md) to 260.104 amu (260Md).

See also


  1. "Transuranic elements" are the chemical elements with atomic numbers greater than that of uranium (atomic number 92).

ISBN links support NWE through referral fees

  • Emsley, John. Nature's Building Blocks: An A–Z Guide to the Elements. Oxford: Oxford Univ. Press, 2001. ISBN 0198503407
  • Greenwood, N.N., and A. Earnshaw. Chemistry of the Elements 2nd ed. Oxford, UK; Burlington, MA: Butterworth-Heinemann, 1998. ISBN 0750633654
  • Hampel, Clifford A. The Encyclopedia of the Chemical Elements. New York: Reinhold Book Corp, 1968. ISBN 0442155980
  • Morss, Lester R., Norman M. Edelstein, and Jean Fuger. The Chemistry of the Actinide and Transactinide Elements. 3rd ed. 5 vols. Joseph J. Katz, adapter. Dordrecht: Springer, 2006. ISBN 1402035551
  • Stwertka, Albert. Guide to the Elements. Rev. ed. Oxford: Oxford University Press, 1998. ISBN 0-19-508083-1

External links

All links retrieved November 8, 2022.


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