Mendelevium

Mendelevium is synthetic element first discovered in 1955 by bombardment of alpha particles on einsteinium. It has no uses outside basic scientific research.

History and Discovery

Mendelevium is a synthetic element and ninth transuranic element. It was synthesized by Stanley G. Thompson with his team members Albert Ghiorso, Bernard G. Harvey, Glenn T. Seaborg, Gregory Robert Choppin at University of California, Berkeley [1]. It was first synthesized in early 1955. It was produced in the 60 inch cyclotron at Berkeley Radiation Laboratory by bombarding einsteinium atoms with alpha particles, forming 17 atoms the first time. It is the first element which was synthesized one atom at a time. Mendelevium cannot be synthesized using the method of neutron capture which was used to synthesize preceding transuranic elements because, one, the beta decaying isotope of fermium that would be able to produce the next element was not known, secondly, the very short half-life to spontaneous fission of fermium isotope added to the impossibility of neutron capture process. It was named after Dmitri Mendeleev who formulated the Periodic Law and was also known as the father of the periodic table of chemical elements.

Mendelevium

Periodic Table Classification	Group n/a Period 7
State at 20C	Solid (predicted)
Color	n/a
Electron Configuration	[Rn] 5f13 7s2
Electron Number	101
Proton Number	101
Electron Shell	2, 8, 18, 32, 31, 8, 2
Density	10.30 g.cm-3 at 20°C (predicted)
Atomic number	101
Atomic Mass	258.00 g.mol -1
Electronegativity according to Pauling	1.30

Occurrence

Mendelevium is a synthetic element which is not found naturally [2]. Mendelevium isotopes are usually produced by bombarding bismuth targets with heavy argon ions or by the bombardment of lighter ions of carbon and nitrogen on plutonium and americium targets. All the isotopes of mendelevium are highly unstable and decay into einsteinium through alpha decay or it decays through spontaneous fission.

Physical Characteristics

Mendelevium has not yet been prepared in macroscopic quantity so not much is known about its physical characteristics. It is classified as metal and is solid at room temperature. Mendelevium melting point is predicted to be at 827 degree centigrade while it is expected to have a density of 10.3 g/cm³[3]. Mendelevium belongs to the actinide series and has an atomic number 101 while it is represented by symbol Md.

Chemical Characteristics

Mendelevium mostly exits in +3 oxidation state but oxidation state of +2 can also be seen making its chemistry similar to that of late actinides.

Significance and Uses

• Mendelevium has currently no known uses apart from its use in basic scientific research.

Health Effects

Not much data of toxicity of mendelevium is available because of it being a rare element. It does not occur naturally and also has relatively short half-life.

Isotopes of Mendelevium

Mendelevium has 16 known isotopes. The mass number of these isotopes ranges from 245 to 260. All the isotopes of mendelevium are radioactive with the most stable isotope mendelevium -258 having half-life of 51.5 days. The next stable isotope is mendelevium-260 which has a half-life of 31.8 days. All the remaining isotopes have half-life ranging from few hours to less than 5 minutes. Mendelevium-256 has a half-life of 1.17 hours and is the most commonly used isotope for experimentation because of its ease of production [4]. Mendelevium has five nuclear isomers with the longest lied isomer mendelevium-258m.

REFERENCES

[1]. Ghiorso, A.; Harvey, B.; Choppin, G.; Thompson, S.; Seaborg, Glenn T. (1955). “New Element Mendelevium, Atomic Number 101”. Physical Review. 98 (5): 1518–1519.

[2]. Fournier, Jean-Marc (1976). “Bonding and the electronic structure of the actinide metals”. Journal of Physics and Chemistry of Solids. 37 (2): 235–244.

[3]. Choppin, Gregory R. (2003). “Mendelevium”. Chemical and Engineering News. 81 (36).

[4]. Hofmann, Sigurd (2002). On beyond uranium: journey to the end of the periodic table. CRC Press. pp. 40–42.