Elements discovered by atomic bombardment

Edited, with a chapter on Elements Discovered by Atomic Bombardment,... 

It is a pleasure to acknowledge the kind assistance given by Dr. E. H. S. Bailey and Dr. Selma Gottlieb Kallis, who read portions of the manuscript, by Dr. F. B. Dains, who made many helpful suggestions as to sources of material and furnished most of the illustrations, by Dr. Max Speter, who read the proof for the fourth edition, and by Dr. Henry M. Leicester, who read the manuscript of the sixth edition and wrote the chapter on Elements Discovered by Atomic Bombardment. ... 

Discovery of the Elements, M. E. Weeks, edited, with a chapter on elements discovered by atomic bombardment, by H. M. Leicester, 6 ed.. Journal of Chemical Education, Easton, PA (1956). 

The discovery that a transmutation had happened started a flood of research. Soon after Harkins and Blackett had observed a nitrogen atom forming oxygen, other transmutation reactions were discovered by bombarding various elements with alpha particles. As a result, chemists have synthesized, or created, more elements than the 93 that occur naturally. These are synthetic elements. All of the transuranium elements, or those with more than 92 protons in their nuclei, are synthetic elements. To make them, one must use special equipment, called particle accelerators, described below. 

When Fermi s group analyzed the products of the neutron bombardment, it appeared to them that radium had been produced, especially since they had no reason to even suspect that barium could be a product. Since radium is the daughter element formed by two successive alpha decays of a uranium atom, they decided their quest for a transuranium element was unsuccessful. Subsequently, Otto Hahn (1879-1968), Fritz Strassmann (1902-80), and Lise Meitner (1878-1968), all from Germany, reinterpreted the results to show that it was not radium atoms that had been formed, but barium atoms instead from the nuclear fission of uranium. Thus, Fermi and his group just missed discovering fission. 

Mendelevium — (Dmitri Mendeleev [1834-1907]), Md at. wt. (258) at. no. 101 m.p. 827°C valence +2, +3. Mendelevium, the ninth transuranium element of the actinide series to be discovered, was first identified by Ghiorso, Harvey, Choppin, Thompson, and Seaborg early in 1955 as a result of the bombardment of the isotope Es with helium ions in the Berkeley 60-inch cyclotron. The isotope produced was Md, which has a half-life of 78 min. This first identification was notable in that Md was synthesized on a one-atom-at-a-time basis. Nineteen isotopes and isomers are now recognized. Md has a half-life of 51.5 days. This isotope has been produced by the bombardment of an isotope of einsteinium with ions of helium. It now appears possible that eventually enough Md can be made so that some of its physical properties can be determined. Md has been used to elucidate some of the chemical properties of mendelevium in aqueous solution. Experiments seem to show that the element possesses a moderately stable dipositive (II) oxidation state in addition to the tripositive (III) oxidation state, which is characteristic of actinide elements. 

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