Mendelevium

What is Mendelevium?

Mendelevium is a highly radioactive, synthetic element in the actinide series. It is denoted by the symbol Md and atomic number 101. It can only be produced by bombarding lighter elements with charged molecules. American chemists Bernard G Harvey, Stanley G Thompson, Albert Ghiorso, Glenn T. Seaborg and Gregory R Choppin discovered the element in 1955 at University of California, Berkeley. They discovered it by bombarding alpha particles (helium ions) with a minute amount of einsteinium-253. The element is named after the father of the periodic table and Russian chemist Dmitry Mendeleev.

The chemistry of Mendelevium isotopes is distinctive for the late actinides, with a majority of the +3 oxidation state but also a nearby +2 oxidation state. The most stable isotope is Mendelevium-258. It has a half-life of around 51.5 days. Later it decays to einsteinium-254 by the process of alpha decay or spontaneous fission hence all the isotopes of mendelevium have a shorter life. 16 isotopes of Mendelevium are acknowledged, with mass numbers from Md 245 to Md 260. All isotopes are radioactive.

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Properties of Mendelevium

Physical Properties 

1. Atomic number 101

2. Atomic mass number- 258

3. Position in periodic table-Period 7, block- f, group- actinides

4. State at 200 C- Solid

5. Electron Configuration of gaseous state- [Rn] 5f¹³ 7s²

6. Stablest isotope- Mendelevium-258

7. Oxidation states- +2, +3

8. Melting Point - 1100 K or 15210 F or 8270 C

9. The gravity and boiling point are still unknown

10. The Chemical Abstract Service registry number (CAS) is 7440-11-1

11. Key isotopes- 258Md, 260Md  

12. Its colour is unknown but it is considered metallic or silvery white or grey.  

Chemical Properties

1. Till date, chemical reactions are carried out only in solutions with +2 or +3 oxidation states. Though the +1 state has been reported to be found out but not yet confirmed.

2. It is trivalent in aqueous solution.

3. It forms insoluble fluorides and hydroxides that are condensed with trivalent lanthanide salts.

4. The mendelevium elutes during carbon-exchange bonding.

5. It has a smaller ionic radius than that of the previous actinide (Fermium) in the periodic table.

6. Mendelevium(III) can be reduced to Mendelevium(II) easily. It acts stable in aqueous solution. 

7. It is neutral in water-ethanol solution and analogous or homologous to caesium.

8. It behaves like divalent elements when reduced.

9. On co crystallizing Mendelevium with chlorides, form mixed crystals with divalent elements.

10. It tends to decay.

11. It has 16 synthetic isotopes whose mass number lies between 245-260.

Production in Laboratories

• Mendelevium is still produced in the same way as it was produced the first time in an all-night experiment. The lightest isotopes 245Md to 247Md are produced through the bombardment of Bismuth with heavy Argon ions in a 60-inch cyclotron. 

• Slightly heavier isotopes are produced by bombardment Plutonium with Carbon ions and Americium with Nitrogen ions in the cyclotron. The most stable 258Md isotope is produced by bombarding einsteinium with alpha particles. 

• The recoil momentum of produced Md takes it apart from the einsteinium target. Then it is brought on to a thin metal foil in a vacuum. This process eliminates the need for immediate chemical separation. 

• Md atoms are separated from metal foil by using fission products. Then Md atoms are trapped in a gaseous atmosphere, the jet of gas carries it along. Using the capillary tubes having potassium chloride aerosols in helium gas, Md atoms are transported over a short distance. 

• An alternative technique to isolate Mendelevium incorporates the discrete elution properties of Md from those of einsteinium and fermium. 

• The preliminary steps are the same as above, and engages HDEHP for abstraction chromatography, but coprecipitates the mendelevium with terbium fluoride instead of lanthanum fluoride. Then Chromium is introduced to the Mendelevium to condense it in hydrochloric acid with Zinc or Mercury 

• The solvent extraction takes place, and even though the tetravalent lanthanides and trivalent and actinides stay on the column, It is again oxidized to the +3 state using hydrogen peroxide and then isolated by elution with hydrochloric acid (to eliminate impurities and chromium) and finally hydrochloric acid (to extract the mendelevium). 

• It is also advisable to use a column of zinc and cationic amalgam, using 1 M hydrochloric acid as an eluent, reducing Mendelevium(III) to Md(II) where it behaves like the alkaline metals. 

Isotopes of Md

• The most stable Isotope after Md-256 is Md-257 and Md 260. All rest have a life span less than an hour.

• The lifespan of Md isotopes shows growth after Md-245 but again decreases from Md-256.

Uses of Mendelevium

1. As it has a shorter life, it is produced in smaller quantities. It has no commercial use. It is mainly used for research purposes only.

2. The isotope 256Md is used to study the behaviour of mendelevium in aqueous solution.

3. It is used in the synthesis of other heavy atomic nuclei.