Isotopic Classification of the Elements

An element is specified by the number of protons in its nucleus. This equals the atomic number Z of the respective element and determines its place within the periodic table of the elements. The atomic number is given as a subscript preceding the elemental symbol, e.g., gC in case of carbon. Atoms with nuclei of the same atomic number differing in the number of neutrons are termed isotopes. One isotope differs from another isotope of the same element in that it possesses a differ- 

Mass Spectrometry, 2nd ed., DOI 10.1007/978-3-642-10711-5 3, Springer-Verlag Berlin Heidelberg 2011 

Note The mass number must not be confused with the atomic number of an element. For the heavier atoms there can be isotopes of the same mass number belonging to different elements, e.g., the most abundant isotopes of both igAr and 2oCa have mass number 40. 

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R. W. FairbriiXjE, Encyclopedia of Geochemistry and Environmental Sciences, Van Nostrand, New York, 1972.. See sections on Geochemical Classification of the Elements Sulfates Sulfate Reduction-Microbial Sulfides Sulfosalts Sulfur Sulfur Cycle Sulfur Isotope Fractionation in Biological Processes, etc., pp. 1123 - 58. 

Isotopic abundances are listed either as their sum being 100 % or with the abundance of the most abundant isotope normalized to 100 %. The latter is used throughout this book because this is consistent with the custom of reporting mass spectra normalized to the base peak (Chap. 1). The isotopic classifications and isotopic compositions of some common elements are listed below (Table 3.1). A full table of the elements is included in the Appendix. 

Following the classification of the analytical methods given by ISO 32 [3] two major type of calibration materials can be certified. For relative methods such as all spectrometric ones, pure substances are necessary. They can be certified for the stoichiometry and degree of purity but also for isotopic composition. The latter case is a prerequisite for measurements of radioactive materials and for stable isotope mass spectrometry (isotope dilution TIMS or ICP-MS). For comparative methods, pure substances and mixtures of substances are necessary, as well as matrix materials for which the element to be determined is perfectly known and also the major compounds that produce a matrix influence on the signal (e.g. alloys, gases). 

The chemistry, and hence hazards, of hot, or radioactive, elements parallels that of their cold isotopes. However, the radiation poses additional toxicity hazards. A qualitative classification of selected isotopes in terms of their toxicity is given in Table 10.2. The biological effects of ionizing radiation stem mainly from damage to individual cells following ionization of the water content. Oxidizing species, e.g. hydrogen peroxide. 

SNIF-NMR and/or IRMS techniques were often combined with trace element analyses (ICP-MS, ICP-OES, FAAS, ETAAS, GFFA) and chemometrics for the geographical characterization of wines. In a relatively old paper, Day et ah (1995) analyzed 165 grape samples collected in 1990 in four different production areas of France (Alsace, Beaujolais, Burgundy, and the Loire Valley). The combined use of isotopic and trace element data allowed an excellent classification of wine samples corresponding to... 

Until vciy recently only ninety-two elements were recognized and the periodic classification ended with the element uranium. In 1940 McMii.i.an and Abelson showed that bombardment of uranium witli neutrons led to the production of an isotope of a new clement, neptunium, of atomic number 93. Diis isotope whu h has a half life period of 2 3 days,... 

Discussion of processes for industrial separation of uranium isotopes cannot be as complete as the discussion of deuterium separation in Chap. 13. The detailed technology of the most economical and most promising processes is subject to security classification and to proprietary restrictions. Nevertheless, processes for enriching uranium can be described in sufficient detail to make their principles clear and to illustrate the similarities and differences between them and processes for separating isotopes of light elements. 

Now it is clear that radioelements are just isotopes of natural radioactive elements. The three emanations are the isotopes of the radioactive element radon, the number 86 in the periodic system. The radioactive families consist of the isotopes of uranium, thorium, polonium, and actinium. Later many stable elements were found to have isotopes. An interesting observation may be made here. When a stable element was discovered this meant simultaneous discovery of all its isotopes. But in the cases of natural radioactive elements individual isotopes were discovered first. The discovery of radioelements was the discovery of isotopes. This was a significant difference between stable and radioactive elements in connection with the search for them in nature. No wonder that the periodic system was badly strained when accommodation had to be found for the multitude of radioelements,—it was a classification of elements, after all, not isotopes. The discovery of the displacement law and isotopy greatly clarified the situation and paved the way for future advances. 

The discovery of isotopy initially presented certain dangers for the periodic system. The large number of new isotopes that were discovered suggested that there were many more atoms, in the sense of smallest possible particles, of any particular element than had previously been recognized. Some chemists even suggested that the periodic table would have to be abandoned in favor of a classification system that included a separate place for every single isotope. Luckily, this idea was resisted since, as it turned out, isotopes of the same element showed identical chemical properties. ... 

A complete list of these radio-elements, including their eventual classification as isotopes of existing elements, can be found in the appendices of A.J. Hide, The Development of Modern Chemistry, Dover Pubheations, New York, 1984. 

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