Mendelevium Facts

Also Known as Element 101 or Md

Mendelevium is element atomic number 101
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Mendelevium is a radioactive synthetic element with atomic number 101 and element symbol Md. It is expected to be a solid metal at room temperature, but since it is the first element that can't be produced in large quantities by neutron bombardment, macroscopic samples of Md have not been produced and observed.

Facts About Mendelevium

  • Mendelevium is a synthetic element that has not been detected in nature. It was produced in 1955 by bombarding the element einsteinium (atomic number 99) with alpha particles to produce mendelevium-256. It was produced by Albert Ghiorso, Glenn T. Seaborg, Gregory Robert Choppin, Bernard G. Harvey, and Stanley G. Thompson at the University of California at Berkeley in 1955. Element 101 was the first element to be produced one atom at a time.
  • According to Glenn Seaborg, the naming of the element was somewhat controversial. He said, "We thought it fitting that there be an element named for the Russian chemist Dmitri Mendeleev, who had developed the periodic table. In nearly all our experiments discovering transuranium elements, we'd depended on his method of predicting chemical properties based on the element's position in the table. But in the middle of the Cold War, naming an element for a Russian was a somewhat bold gesture that did not sit well with some American critics." Mendelevium was the first of the second hundred chemical elements. Seaborg requested and received permission to name the new element for a Russian from the U.S. government. The proposed element symbol was Mv, but the IUPAC changed the symbol to Md at their assembly in Paris in 1957.
  • Mendelevium is produced by bombarding bismuth targets with argon ions, plutonium or americium targets with carbon or nitrogen ions, or einsteinium with alpha particles. Starting with einsteinium, femtogram samples of element 101 may be produced.
  • Mendelevium properties are largely based on predictions and on the activity of homologous elements on the periodic table because bulk preparation of the element isn't possible. The element forms trivalent (+3) and divalent (+2) ions. These oxidation states have been shown experimentally in solution. The +1 state has been reported, as well. The density, state of matter, crystal structure, and melting point have been estimated based on the behavior of nearby elements on the table. In chemical reactions, mendelevium behaves much like other radioactive transition metals and sometimes like an alkaline earth metal.
  • At least 16 isotopes of mendelevium are known, which have mass numbers ranging from 245 to 260. All of them are radioactive and unstable. The longest-lived isotope is Md-258, which has a half-life of 51.5 days. Five nuclear isotopes of the element are known. The most important isotope for research, Md-256, decays via electron capture about 90% of the time and alpha decay otherwise.
  • Because only small amounts of mendelevium can be produced and its isotopes have short half-lives, the only uses for element 101 are scientific research into the element's properties and for the synthesis of other heavy atomic nuclei.
  • Mendelevium serves no biological function in organisms. It's toxic because of its radioactivity.

Mendelevium Properties

  • Element Name: mendelevium
  • Element Symbol: Md
  • Atomic Number: 101
  • Atomic Weight: (258)
  • Discovery: Lawrence Berkeley National Laboratory - USA (1955)
  • Element Group: actinide, f-block
  • Element Period: period 7
  • Electron Configuration: [Rn] 5f13 7s2 (2, 8, 18, 32, 31, 8, 2)
  • Phase: predicted to be a solid at room temperature
  • Density: 10.3 g/cm3 (predicted near room temperature)
  • Melting Point: 1100 K ​(827 °C, ​1521 °F) (predicted)
  • Oxidation States: 2, 3
  • Electronegativity: 1.3 on the Pauling scale
  • Ionization Energy: 1st: 635 kJ/mol (estimated)
  • Crystal Structure: face-centered cubic (fcc) predicted


  • Ghiorso, A., et al. “New Element Mendelevium, Atomic Number 101.” Physical Review, vol. 98, no. 5, Jan. 1955, pp. 1518–1519.
  • Lide, David R. "Section 10: Atomic, Molecular, and Optical Physics; Ionization Potentials of Atoms and Atomic Ions." Crc Handbook of Chemistry and Physics, 2003-2004: A Ready-Reference Book of Chemical and Physical Data. Boca Raton, Fla: CRC Press, 2003.
  • Edelstein, Norman M. "Chapter 12. Chemistry of the Heaviest Actinides: Fermium, Mendelevium, Nobelium, and Lawrencium". Lanthanide and Actinide Chemistry and Spectroscopy. Washington, DC: American Chemical Soc, 1980.
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Helmenstine, Anne Marie, Ph.D. "Mendelevium Facts." ThoughtCo, Aug. 26, 2020, Helmenstine, Anne Marie, Ph.D. (2020, August 26). Mendelevium Facts. Retrieved from Helmenstine, Anne Marie, Ph.D. "Mendelevium Facts." ThoughtCo. (accessed June 7, 2023).