Mendelevium (Md)

Mendelevium is a radioactive chemical element with atomic number 101 in the periodic table. Since it’s a synthetically produced chemical, it does not occur naturally in Earth’s crust. As a member of the actinide series of the periodic table, this radioactive rare earth metal presumably has two and three valence electrons, which have been determined by the radioactive tracer technique. 

Chemical and Physical Properties of Mendelevium

Atomic number101
Atomic weight (mass)(258) g.mol-1
Group (number)Actinides
ColorPresumably silvery-white or grey with a metallic luster
Physical statePresumably solid metal at 20°C
Half-lifeFrom less than 0.90(25) milliseconds to
Electronegativity according to Pauling1.3
Melting point827°C, 1521°F, 1100 K
Boiling pointUnknown
Van der Waals radiusUnknown
Ionic radiusUnknown
Most characteristic isotope258Md, 260Md
Electronic shell[Rn] 5f12 6d1 7s2
The energy of the first ionization6.58 [eV]
The energy of the second ionization
Discovery dateIn 1955 by Albert Ghiorso and his team at UC Berkeley

The chemical properties of mendelevium are mainly based on predictions. With the periodic table symbol Md, this synthetic transuranium element of the actinide series is classified under the atomic number 101, with an assumed atomic mass of (258) g.mol-1, and determined electron configuration [Rn] 5f12 6d1 7s2

While the melting point of mendelevium is achieved at 827°C (1521°F, 1100 K), the boiling point of this highly radioactive substance has not yet been determined. In addition, mendelevium’s electronegativity according to Pauling is 1.3, while the atomic radius according to van der Waals is unknown.

How Was Mendelevium Discovered?

In 1955, a team of scientists led by Albert Ghiorso managed to produce the ninth synthetic transuranium element of the actinides family at the Lawrence Berkeley National Laboratory, California, United States. 

The team consisted of the American chemists Albert Ghiorso, Bernard G. Harvey, Gregory R. Choppin, Stanley G. Thompson, and Glenn T. Seaborg. These scientists attempted a helium-ion (alpha-particle) bombardment of a minute quantity of einsteinium-253 (a lighter element with atomic number 99) in a 60-inch cyclotron. 

By targeting about a billion einsteinium atoms in the particle accelerator, the team of chemists eventually succeeded in producing the first of the trans-fermium elements, i.e. the 256Md isotope of mendelevium with a half-life of 77 minutes. The other mendelevium isotopes produced in the repeated experiment were identified by the ion-exchange adsorption-elution method. Namely, this method provided scientific evidence of mendelevium behaving like its rare-earth homolog –  thulium (Tm). 

The team of scientists published their scientific findings on the newly discovered element in the 1955 June issue of Physical Review Letters, suggesting the name mendelevium for it. 

How Did Mendelevium Get Its Name?

By giving the name of the great Russian chemist to the new element they produced, the team of scientists led by Ghiorso paid tribute to Dmitri Mendeleev for his pioneering work in the field of chemistry as the first chemist to use the periodic table as a system to predict the chemical properties of undiscovered elements.

The Controversy around the Name of the Element

Mendelevium was discovered in the middle of the Cold War between the United States and the Soviet Union. Since the American team of scientists wanted to honor the Russian chemist Mendeleev by naming their newly discovered element after him, the idea didn’t sit well with the American public at the time.

Seaborg requested and received permission from the U.S. government to proceed with the team’s proposition regarding the name of the new element. The suggested symbol of the element was Mv. However, the IUPAC (International Union of Pure and Applied Chemistry) changed the element’s symbol to Md at the assembly held in Paris, in 1957.

Dmitri Mendeleev and the Invention of the Periodic Table of Elements 

Dmitry Ivanovich Mendeleyev (1834 – 1907) is a Russian chemist who pioneered the classification of elements by creating the periodic table – one of the most iconic symbols of modern chemistry. According to his observations, if all known chemical elements are arranged in order of the increasing atomic weight, they display a recurring pattern that gathers them in families of elements that share similar chemical and physical properties. 

In his first attempt to make a practical realization of his scientific vision, Mendeleev wrote the atomic numbers of the 65 chemical elements that were then known on separate cards. On the back of each card, the great chemist added the properties of the elements, after which he arranged them according to the increasing atomic weight of the substance.

At that point, he noticed that the atomic weight plays a key role in the periodicity of the table he envisioned. It seemed like the elements resemble the chemical and physical properties of the neighbouring  chemicals as their atomic number increased. 

In 1871, Mendeleev presented this periodicity of elements in the first version of the periodic table. There were gaps among the fields on the periodic table that were predicted to be filled with elements yet to be discovered. Mendeleev’s observation of elements was so accurate, that he even predicted the properties and atomic masses of several unknown elements. 

Mendeleev even had a solution for those elements whose properties didn’t match the prediction. The answer of the famed Russian chemist to this potential problem was quite logical: he presumed it quite likely that they had an incorrectly measured atomic weight.   

Where Can You Find Mendelevium?

Element 101 does not occur naturally in the Earth’s crust. Mendelevium is a synthetic element that is produced by bombarding bismuth targets with argon ions, plutonium or americium targets with carbon or nitrogen ions, and einsteinium with alpha particles.

Mendelevium in Everyday Life

Since its discovery, the chemical element mendelevium hasn’t been produced in larger quantities so that it can have a wider everyday application. The few existing atoms of mendelevium are used for scientific research of the element’s properties.

How Dangerous Is Mendelevium?

As a highly radioactive element, mendelevium may impose a severe health hazard if it exists in greater quantities. On the other hand, even if there were larger quantities of this chemical produced, the radioisotopes of mendelevium are too short-lived to be considered as potential triggers of adverse health effects. 

Environmental Effects of Mendelevium

Since only minuscule amounts of mendelevium have been produced so far, this chemical element cannot be regarded as an environmental hazard. 

Isotopes of Mendelevium

The elemental form of mendelevium is made up of the mendelevium-256 isotope. This chemical element counts 16 isotopes with mass numbers ranging from 245Md to 260Md. Among them, there are no stable isotopes, because all forms of this transuranium actinide element have been synthetically produced and are highly radioactive. 

With a half-life of 51.3 days, the mendelevium-258 isotope is the most stable radioisotope of mendelevium. This form of mendelevium decays into einsteinium-254 through alpha decay or via spontaneous fission.

The following is a tabular presentation of the mendelevium isotopes:



[n 1]

ZNIsotopic mass (Da)


[n 2][n 3]




[n 4]




Spin and



[n 5][n 6]

Excitation energy[n 6]
244Md[1]101143 0.4+0.4


−0.1 s[2]

245Md101144245.08081(33)#0.90(25) msSF(various)(1/2−)#
α (rare)241Es
246Md101145246.08171(28)#1.0(4) sα242Es 
β+ (rare)246Fm
247Md101146247.08152(22)#1.12(22) sSF(various)1/2−#
α (rare)243Es
248Md101147248.08282(26)#7(3) sβ+ (80%)248Fm 
α (20%)244Es
β+, SF (.05%)(various)
249Md101148249.08291(22)#24(4) sα (60%)245Es(7/2−)
β+ (40%)249Fm
250Md101149250.08442(32)#52(6) sβ+ (93%)250Fm 
α (7%)246Es
β+, SF (.02%)(various)
251Md101150251.084774(20)4.0(5) minβ+ (90%)251Fm7/2−#
α (10%)247Es
252Md101151252.08643(14)#2.3(8) minβ+ (50%)252Fm 
α (50%)248Es
253Md101152253.08714(3)#12(8) min


[6(+12−3) min]

254Md101153254.08959(11)#10(3) minβ+254Fm(0−)
α (rare)250Es
255Md101154255.091084(7)27(2) minβ+ (92%)255Fm(7/2−)
α (8%)251Es
SF (.15%)(various)
256Md101155256.09389(13)#77(2) minβ+ (89%)256Fm(1−)
α (11%)252Es
257Md101156257.0955424(29)5.52(5) hEC (84.8%)257Fm(7/2−)
α (15.2%)253Es
SF (1%)(various)
258Md101157258.098431(5)51.5(3) dα (99.99%)254Es(8−)#
β (.0015%)258No
β+ (.0015%)258Fm
259Md[n 7]101158259.10051(22)#1.60(6) hSF (98.7%)(various)7/2−#
α (1.3%)255Es
260Md101159260.10365(34)#27.8(8) dSF (85%)(various) 
α (5%)256Es
EC (5%)260Fm
β (3.5%)260No

Source: Wikipedia

Mendelevium Compounds 

Mendelevium is a synthetic and highly unstable element due to its radioactive properties. That’s why it does not participate in any compounds to date. Studies on this element conducted with the help of radioactive tracer techniques show that the assumed oxidation state of mendelevium would be +3, according to its position in the actinides series. The less stable +2 oxidation state has also been observed. 

5 Interesting Facts and Explanations

  1. Mendelevium was discovered as the ninth element in the line of the actinide series of the periodic table. 
  2. The 256Md isotope was not only the first mendelevium form to be synthesized, but also the first isotope of any chemical element that was produced one atom at a time, due to a technical obstacle.
  3. The alpha irradiation of the einsteinium target took place over three hours because the cyclotron was located in the University of California campus, while the Radiation Laboratory was in a more remote location. This inconvenience required a more complex approach to the performance of the experiment.
  4. This transuranium chemical is also the first element classified by its atomic number that cannot be synthesized in quantities visible to the naked eye via neutron bombardment of the lighter elements.
  5. All actinides can exist in both divalent and trivalent states.