Mendelevium Element Facts

The chemical element mendelevium is classed as actinide metal. It was discovered in 1955 by Albert Ghiorso, Bernard Harvey, Gregory Choppin, Stanley Thompson, and Glenn Seaborg.

60-inch cyclotron.
Mendelevium was first made in the 60 inch Berkeley cyclotron

Many transuranium elements including mendelevium were discovered using the 60-inch cyclotron at the University of California Lawrence Radiation Laboratory, Berkeley.


Data Zone

Classification: Mendelevium is an actinide metal
Atomic weight: (258), no stable isotopes
State: solid
Melting point: 827 oC, 1100 K
Boiling point:
Electrons: 101
Protons: 101
Neutrons in most abundant isotope: 157
Electron shells: 2,8,18,32,31,8,2
Electron configuration: [Rn] 5f12 7s2
Density @ 20oC:
Show more, including: Heats, Energies, Oxidation, Reactions, Compounds, Radii, Conductivities
Atomic volume:
Structure: close packed cubic
Specific heat capacity
Heat of fusion
Heat of atomization
Heat of vaporization
1st ionization energy 635 kJ mol-1
2nd ionization energy
3rd ionization energy
Electron affinity
Minimum oxidation number 0
Min. common oxidation no. 0
Maximum oxidation number 3
Max. common oxidation no. 3
Electronegativity (Pauling Scale) 1.3
Polarizability volume 18.2 Å3
Reaction with air
Reaction with 15 M HNO3
Reaction with 6 M HCl
Reaction with 6 M NaOH
Atomic radius
Ionic radius (1+ ion)
Ionic radius (2+ ion)
Ionic radius (3+ ion) 89.6 pm
Ionic radius (1- ion)
Ionic radius (2- ion)
Ionic radius (3- ion)
Thermal conductivity
Electrical conductivity
Freezing/Melting point: 827 oC, 1100 K

Mendelevium Radioactive

Mendelevium is Radioactive.

Discovery of Mendelevium

Dr. Doug Stewart

Mendelevium was the ninth synthetic transuranium element of the actinide series to be discovered.

It was first identified by Albert Ghiorso, Bernard Harvey, Gregory Choppin, Stanley Thompson, and Glenn Seaborg in 1955 at the Lawrence Berkeley National Laboratory, California.

Mendelevium-256 (half-life 78.1 minutes) was produced by bombarding einsteinium-253 with alpha particles in the Berkeley 60-inch cyclotron.

Only 17 atoms of mendelevium-256 were initially produced in an all night experiment predicted to produce just one or two atoms of product every three hours. Each nuclear reaction created mendelevium-256 and a neutron. (1), (2), (3)

Mendelevium was identified by chemical analysis in an ion exchange experiment. (1)

The element is named after the Russian chemist Dmitri Mendeleev who devised the first periodic table in modern form.

Transuranium elements discovery and experiments. 1963 chemistry educational documentary narrated by Glenn Seaborg, Stanley Thompson and Albert Ghiorso.

Appearance and Characteristics

Harmful effects:

Mendelevium is harmful due to its radioactivity.


Mendelevium is a synthetic, highly radioactive metal and has only been produced in miniscule amounts.

Mendelevium was the first element to be produced one atom at a time.

Mendelevium metal has not been prepared. (3a)

Uses of Mendelevium

Mendelevium is of scientific research interest only.

Abundance and Isotopes

Abundance earth’s crust: nil

Abundance solar system:

Cost, pure: $ per g

Cost, bulk: per 100g

Source: Mendelevium is a synthetic element and is not found naturally. Mendelevium is produced through charged-particle of lighter elements in particle accelerators.

Isotopes: Mendelevium has 16 isotopes whose half-lives are known, with mass numbers 245 to 260. Mendelevium has no naturally occurring isotopes. Its longest lived isotopes are 258Md with a half-life of 51.5 days, 260Md, with a half-life of 31.8 days and 259Md with a half-life of 96 minutes.


1. Glenn 1. Seaborg, The Transcalifornium Elements., Journal of Chemical Education, Vol 36.1 (1959) p39.
2. John Emsley, Nature’s building blocks: an A-Z guide to the elements., Oxford University Press, 2003., p458.
3. Robert J. Silva, The Chemistry of the Actinide and Transactinide Elements., Springer., Vol 3.13, p1630 – 1631.
3a. Robert J. Silva, The Chemistry of the Actinide and Transactinide Elements., Springer., Vol 3.13, p1634.

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