The confusing feature of all these newly discovered elements was that in many instances some of them had very similar, and perhaps identical, chemical properties - even though they had different half-lives. These elements included “ionium,” “brevium,” “actinouranium,” “radiothorium,” “niton,” “actinon,” “thorium-X,” “uranium-X,” and dozens more. Rutherford’s finding led to the discoveries by other investigators of a plethora of new elements in other decay schemes during the first decade of 1900. For example, Rutherford observed that radium decays through a series of steps, giving a sequence Ra (radium) → Rn (radon) → Ra-A → Ra-B → Ra-C → Ra-E → Ra-F → Ra-G. However, a difficulty emerged - a glut of elements was appearing, each with a different half-life. The major technique in tracing these elements was simply following their radioactivity in various chemical fractions as analytical procedures were being developed. Marie Curie Pierre Curie Ernest Rutherford Frederick Soddy By the 1920s only elements 43, 61, 85, and 87 remained unknown (although several spurious claims had been made). All these elements seemed to fit in the periodic table, filling remaining gaps. The next year André Debierne (1874-1949) in the Curie research group discovered actinium in the same ore, and the following year in North America radon was discovered in 1900 by Ernest Rutherford (1871-1937) and Frederick Soddy (1877-1956) in Montreal, Canada.* Independently protactinium was discovered in 1917 by Otto Hahn (1879-1968) and Lise Meitner (1878-1968) in Berlin and by Frederick Soddy and John Cranston (1891-1972) in Aberdeen, Scotland. Joachimsthal, Bohemia (now Jáchymov, Czech Republic) and discovered radium and polonium in 1898. She and her husband Pierre Curie (1859-1906) took up a study of the uranium ore from St. The renowned Marie Curie (1867-1934) promptly made a study of all elements (that were known at that time) and determined that only two were radioactive - uranium and thorium. Although the radioactive elements uranium and thorium were discovered early in the history of the elements - 17, respectively, years before the advent of the periodic table - radioactivity itself was unknown until 1896 when Henri-Antoine Becquerel (1852-1908) in Paris found that uranium could expose photographic plates, even when protected by black opaque paper.
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