Radioelement, definition

Definition of radioelement solubility and sorption behaviour requires information concerning effective concentrations or thermodynamic activities of aqueous species a and not simply their concentrations (m,). In very dilute solutions, ai = nii, but as ionic strength increases, there is increasing departure from this ideal behaviour, so that an activity coefficient (7,) must be defined to determine a, ... 

Apart from historical articles, Norwegian journals mainly addressed the periodic system in articles on radioactivity, and only some decades after the system had been published by Mendeleev and Meyer. The discovery of more than thirty new radioactive elements evidently became a puzzle to chemists before the concept of isotopy was introduced by Frederick Soddy (1877-1956) in 1913, chemists were worried about how to fit all the new elements into the periodic system. An instructor at the technical school in Christiania, Haavard Martinsen (1879-1967), conveyed this challenge in an article in Pharmacia, several years before many of the radioelements were recognized as isotopes of known chemical elements. Martinsen, who had spent the previous summer working in William Ramsay s laboratory in London, acknowledged the advantages of Mendeelev s periodic system. However, faced with the evidence that radioelements such as radium emit helium, chemists were, in Martinsen s opinion, left with two options Either to maintain the old established definition of the concept of element and according to this perceive radium and similar substances as common chemical compounds, or to throw the old definition overboard and admit the divisibility of the elements. ... 

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