The Case of Elements 43 and

The Discovery of New Elements and the Boundary Between Physics and Chemistry in the 1920s and 1930s. The Case of Elements 43 and 75 

The search for new elements must undoubtedly have been an appealing enterprise for young chemists around the turn of the century. Eventually, successful research could lead to the most praised reward a Nobel Prize. After the acceptance of the periodic law and system of Dimitrii Mendeleev, the search for yet undiscovered elements became a more organized and rationally based investigation, but nevertheless the identification and manufacture of new elements was made possible only by a set of techniques and instruments developed in the realm of both physics and chemistry. 

After Niels Bohr s proposal of the atomic model and the reinterpretation of the periodic system by Moseley s rule, the search for the missing elements received a new impetus and numerous were the attempts to fill the last gaps in the periodic table. Several rare earths were isolated and, by 1924, only five elements were still to be discovered numbers 43, 61, 75, 85, and 87. Four of those elements are the natural radio-elements 43, 61, 85, and 87 and, for this reason, they escaped the searches led by chemists who were missing the right tool to isolate or even produce them in observable quantities. This was not the case with rhenium (element 75), the last stable element to be discovered and also one of the less abundant in the earth s crust. 

All this suggests that the comparative history of the discovery of elements 43 and 75 constitutes a suitable case study to investigate the boundaries of chemistry and 

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