Mendelevium (Md)

• Element Symbol: Md
• Atomic Number: 101
• Atomic Mass: 258
• Group # in Periodic Table: n/a
• Group Name: Actinides
• Period in Periodic Table: 7
• Block of Periodic Table: f-block
• Discovered by: Stanley G. Thompson, Glenn T. Seaborg, Bernard G. Harvey, Gregory R. Choppin, Albert Ghiorso (1955)

Mendelevium is a synthetic element, which means that it does not exist in nature and can only be made artificially in a lab. So far, twenty synthetic elements—atomic numbers 99 through 118—have been generated. All are unstable and have half-lives ranging from a few hundred microseconds to a year. Mendelevium’s chemical symbol is Md, and its atomic number is 101. It is a metallic, radioactive, transuranic element in the actinide series. These three terms mean that this element looks like a metal, its electrons are unstable, its atomic number is greater than uranium’s, and it is grouped with elements 89 to 103. Mendelevium is the second-to-last actinide and the ninth transuranic element. This element was the first to be produced one atom at a time and therefore has not been produced in large quantities. Another consequence of its production method is that no actual mendelevium metal has ever been created.

In 1955 seventeen atoms of mendelevium were produced during an all-night experiment using the cyclotron at the University of California, Berkeley. This experiment was conducted by Albert Ghiorso, Bernard Harvey, Gregory Chopin, Stanley Thompson, and Glenn Seaborg. In this experiment a sample of einsteinium-253 was bombarded with alpha particles, which are helium nuclei. During the experiment mendelevium-256 was detected. This isotope of mendelevium had a half-life of approximately seventy-eight minutes, which is on the low end of the half-life spectrum for actinides. The group of scientists, however, did not give up. They kept trying and conducted additional experiments that yielded several thousand atoms of mendelevium. Today, it is possible to produce millions of atoms of this element. Interestingly, the longest-lived isotope of the element is mendelevium-260, with a half-life of twenty-eight days. Mendelevium is named after the Russian chemist Dmitri Mendeleev, who developed the first periodic table in a modern arrangement.

Physical Properties

Mendelevium looks like a metal, and its electrons are unstable, making it highly radioactive. The element’s atomic number is greater than uranium’s, and with an atomic number of 101, mendelevium is grouped with elements 89 to 103. Therefore, it is the second-to-last actinide and the ninth transuranic element. In the periodic table mendelevium can be found in the same general neighborhood as the other actinides. The element’s nearest neighbors are fermium to the right and nobelium to the left.

Due to the fact that it is produced one atom at a time, mendelevium metal has never been made, and large-scale production is currently impossible. Yet a couple of predictions have been made regarding its physical properties. First, mendelevium’s predicted standard state at 298 kelvins (K) is solid. Second, its predicted melting point is 827 degrees Celsius (°C). Third, its thermal conductivity is 10 watts per meter-kelvin (W/m·K). These predictions are based on the properties of similar synthetic actinides, such as nobelium. As for its boiling point, density, specific heat, and electrical conductivity, these values are currently unknown. This element has an electron configuration of [Rn] 5f¹³7s².

Chemical Properties

Although many of mendelevium’s physical properties are currently unknown, much is known about its chemical properties. These chemical properties were discovered once the element was put in solution with water. Mendelevium has two confirmed oxidation states (+3 and +2) and one unconfirmed oxidation state (+1). This means that the element is trivalent or extremely electropositive. In other words mendelevium can easily donate electrons to another element that needs them. This is significant because it means that the element can be easily combined with other elements to form compounds. Specifically, after mendelevium was synthesized, Seaborg and Joseph J. Katz in 1955 discovered that the element can and does form insoluble hydroxides (OH⁻) and fluorides (F⁻) that do not dissolve in water. Mendelevium can also chemically react with acetic acid (vinegar).

This element has sixteen known isotopes with mass numbers from 245 to 260. All are unstable and are therefore radioactive. Of these sixteen the longest lived is mendelevium-258, which has a half-life of 51.5 days. The second-most stable isotope is mendelevium-260 (31.8 days), followed by mendelevium-257 (5.82 hours), mendelevium-259 (1.60 hours), and menedelevium-256 (1.27 hours). All of the remaining isotopes have half-lives of less than one hour, with the majority of them having half-lives of less than five minutes. Interestingly, it is mendelevium-256 that is most frequently used in chemical experiments. Despite its relative short half-life, this isotope is used so often because it can be produced in larger quantities than mendelevium-258.

Applications

Because only small quantities of mendelevium have ever been produced, it has no commercial or biological uses, so it its applications are confined to scientific research. Mendelevium-256 has helped scientists understand some of the chemical properties of this element in solution with water.

Mendelevium-258 lives for only about fifty-one days and has absolutely no uses whatsoever. Ironically, although Dmitri Mendeleev, the man who conceived the periodic table in the first place, has been immortalized for his achievement, the element that was named for him is far less important and useful than he was.

Bibliography

Cottrell, T. L. The Strengths of Chemical Bonds. New York: Academic, 1954. Print.

Coursey, J. S., et al. Atomic Weights and Isotopic Compositions with Relative Atomic Masses. NIST Physical Measurement Laboratory. Natl. Inst. of Standards and Technology, 30 Sept. 2015. Web. 13 Nov. 2015.

"Element Mendelevium—Md." EnvironmentalChemistry.com. Barbalace, 1995–2015. Web. 22 Sept. 2015.

Ghiorso, Albert, et al. "New Element Mendelevium, Atomic Number 101." Physical Review 98.5 (1955): 1518–19. Web. 25 Sept. 2015.

Haynes, William M., ed. CRC Handbook of Chemistry and Physics. 95th ed. Boca Raton: CRC, 2014. Print.

Kaye & Laby Tables of Physical & Chemical Constants. Natl. Physical Laboratory, 2015. Web. 25 Sept 2015.

"Technical Data for Mendelevium." The Photographic Periodic Table of the Elements. Element Collection, n.d. Web. 22 Sept. 2015.