Mendelevium discovery

These elements have all been named for famous scientists or for the places of their creation. For example, americium, berkelium, and californium were named after obvious geographical locations. Nobelium was named for the Nobel Institute, although later study proved it was not really created there. Curium was named for Marie Curie, the discoverer of radium. Einsteinium was named for the famous physicist, Albert Einstein. Fermium and lawrencium were named for Enrico Fermi and Ernest O. Lawrence, who made important discoveries in the field of radioactivity. Mendelevium was named for the discoverer of the periodic chart. 

The years after World War II led to the discovery of elements 97-103 and the completion of the actinide series. While the story of the discovery of each of these elements is fascinating, we shall, in the interests of brevity, refer the reader elsewhere (see References) for detailed accounts of most of these discoveries. As an example of the techniques involved, we shall discuss the discovery of element 101 (mendelevium). 

Figure 15.8 Original elution data corresponding to the discovery of mendelevium, February 18, 1955. The curves for einsteinium-253 (given the old symbol E253) and californium-246 are for a-particle emission. (Dowex 50 ion exchange resin was used, and the eluting agent was ammonium a-hydroxyisobutyrate.)...

The discovery of mendelevium, element 101, demanded some fancy footwork on the part of the chemists involved because mendelevium has a half-life of only about half an hour. It was distinctly a matter of chemistry-on-the-run. 

After the discovery of uranium radioactivity by Henri Becquerel in 1896, uranium ores were used primarily as a source of radioactive decay products such as Ra. With the discovery of nuclear fission by Otto Hahn and Fritz Strassman in 1938, uranium became extremely important as a source of nuclear energy. Hahn and Strassman made the experimental discovery Lise Meitner and Otto Frisch provided the theoretical explanation. Enrichment of the spontaneous fissioning isotope U in uranium targets led to the development of the atomic bomb, and subsequently to the production of nuclear-generated electrical power. There are considerable amounts of uranium in nuclear waste throughout the world, see also Actinium Berkelium Einsteinium Fermium Lawrencium Mendelevium Neptunium Nobelium Plutonium Protactinium Rutherfordium Thorium. 

Then there are the people who find their eternal memorial in the kingdom. Lecoq, as we have seen, has had his little joke with gallium. Most people don t presume to give their own names to elements, and the other personal names have all been bestowed by committee in the nominee s honor. It is appropriate that the southern shoreline, including the southern strip of the Southern Island, should commemorate forever—or for as long as we exist— the contributions of Albert Einstein (einsteinium), Enrico Fermi (fermium), Dmitri Mendeleev (mendelevium), Alfred Nobel (nobelium, for stimulation to discovery, maybe, rather than discovery itself), and Ernest Lawrence... 

As the number of new elements grew, so it seemed did the number of researchers involved with each discovery. But there were reasons for this elements were becoming increasingly unstable and shorter lived as they became heavier, and millisecond as well as milligram procedures became important. Mendelevium (number 101) was produced literally one atom at a time, and because of its short half-life, it had to be raced from bombardment to analytical laboratory. Seaborg recounted... 

The history of syntheses saw its periods of breakthroughs and slack periods. The first breakthrough period was from 1940 to 1945 when four transuranium elements were synthesized, namely, neptunium (Z = 93), plutonium (Z = 94), americium (Z = 95), and curium (Z = 96). The period till 1949 was a slack time and no new elements were discovered. In the next breakthrough period from 1949 to 1952 four more transuranium elements were added to the periodic system, namely berklium (Z = 97), californium (Z = 98), einsteinium (Z = 99), and fermium (Z = 100). In 1955, fifteen years after the synthesis of the first transuranium element, one more element, mendelevium (Z = 101), was synthesized. The next 25 years saw much less syntheses and only six new elements appeared in the periodic system. Here scientists encountered an entirely new situation and many former criteria for evaluating discoveries of elements proved inapplicable. 

The new discoveries gave Seaborg and his colleague new targets for bombardment Einsteinium was reacted with hehum ions. The new element Md, mendelevium, was formed, in 1955 at the University of California. 

Hot-fusion reactions were employed in the discoveries of the elements beyond mendelevium as far as element 106, producing the first three members of the domain of superheavy elements. Higher transactinides have also been synthesized in these reactions. As before, the general trends with increasing atomic number were shorter half-lives and smaller production cross sections, a consequence of decreased survival probability in the evaporation process [132, 133]. The probability of decay from the nuclear ground state by spontaneous fission became significant in these elements. The techniques used in the experiments still included radiochemistry and off-line radiation counting [134]. As half-lives dropped below minutes into seconds it became more common to use direct techniques like transportation in gas jets to mechanisms like wheels and tapes (see Sect. 3.3 and Experimental Techniques ). Detection of new nuclides resulted from the detailed... 

The discovery and identification of element 101 (mendelevium, Md) was a landmark experiment in many ways [ 1 ]. It was the first new transuranium element to be produced and identified on the basis of one-atom-at-a-time chemistry and it is also the heaviest element (to date) to be chemically identified by direct chemical separation of the element itself. All of the higher Z elements have been first identified by physical/nuclear techniques prior to study of their chemical properties. In fact, one of the criteria for chemical studies is that an isotope with known properties be used for positive identification of the element being studied. Due to relativistic effects [1] chemical properties cannot be reliably predicted and a meaningful study of chemical properties cannot be conducted with both unknown chemistry and unknown, non-specific nuclear decay properties ... 

The discovery experiments on mendelevium were the first in which the recoil momentum imparted to a product atom during its formation by the bombarding... 

Before its discovery, the trivalent state was predicted to be the most stable in aqueous solution and, therefore, Md was expected to exhibit a chemical behavior similar to the other 3 + actinides and lanthanides [43]. The elution of Md just prior to Fm in the elution sequence of trivalent actinides from a cation-exchange column observed in the discovery experiments appeared to confirm this prediction. Mendelevium forms insoluble hydroxides and fluorides that are... 

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