Composition of the Elements

The smallest particle of an element that retains the composition of the element is called an atom. Details of the nature of atoms are given in Chaps. 3 and 17. The symbol of an element is used to stand for one atom of the element as well as for the element itself. 

P. DeBievre and I.L. Barnes, Table of the isotopic composition of the elements as determined by mass spectrometry, Int. J. Mass Spectrom. Ion Processes, 65 (1985) 211-230. 

As a concluding remark of this section, the theoretical models of nucleosynthesis within stars show that the isotopic compositions of the elements are highly variable depending on star size, metallicity, companion s presence. From the isotopic data obtained in diverse solar system materials it turns out that most of this material was highly homogenized in the interstellar medium or by the formation of the solar system. The presence of isotopic anomalies preserved in some primitive materials are the last witnesses of the initial diversity of the materials constituting our planetary system. 

Because in nature the ground state of a stable nuclide is often attained by decay chains involving intermediate species decaying at different rates, it is worth evaluating the implications of the relative magnitudes of the various decay constants on the isotopic composition of the element. 

The isotopic composition of the elements (including the exact atomic mass and the abundance of the isotopes), the atomic weights of elements, definitions and abbreviations are summarized in Appendix II. 

Mass spectrometric measurements are based on measuring ion currents of separated ion beams of isotopes. With knowledge of the isotopic composition of the elements investigated (see Table of Isotopic Abundances in Appendix I5), a simple identification of chemical elements using singly... 

I he atomic wcighi varies because of natural variations in the isotopic composition of the element, caused by the various isotopes having different origins - I h is the end product of the thorium decay scries, while Ph and " Pb arise Irom uranium as end products of the actinium and radium series respectively. Lead-204 has no existing natural radioactive precursors. Electronic configuration l.v 2s lfc22/j"3v 3//,3i/l"4v- 4/, 4l/" 4/ IJ5v- 5/ "5t/l"bv />-. Ionic radius Pb I.IX A. Pb 1 0.7(1 A. Metallic radius 1.7502 A. Covalent radius (ip i 1.44 A. First ionization potential 7.415 cV second. 14.17 eV. Oxidation... 

Each term in parentheses, gr FL, is one element of F. Because each element of F is a set of elements of G, binary composition of these sets needs to be defined. Binary composition of the elements of F is defined by... 

Results indicate that the leachable elements are contained to some extent within a water soluble component in low and high fusion fly ashes. The leachable amounts of each element are in general related to the bulk composition of the elements in the coal from which the fly ash is produced and the size of the fly ash particles. 

Isotope Ratio Measurements The analysis of milk samples for the accurate determination of its constituent elements has also been done by isotope dilution analysis [34, 102, 103]. For that purpose, an enriched isotope of the element or elements to be determined is spiked to the sample, altering the natural isotopic composition of the element to be analyzed. By measuring the altered... 

If we assume that the isotopic composition of the elements was set by the original processes of nucleosynthesis, deviations from the primordial ratios can originate by ... 

Isotopic Compositions of the Elements 1989, Pure Appl. Chem. 63 (1991) 991-1002. 

The activity of naturally radioactive elements is a measure of their mass. Prerequisites of application of the correlation between mass and activity according to eq. (17.1) are that the isotopic composition of the element to be determined is constant and that interfering radioactive impurities are absent. If the daughter nuelides are also radioactive, radioactive equilibrium must be established or the daughter nuclides must be separated off quantitatively. Interference of radioactive impurities may be avoided by measuring the a or y spectrum of the radionuclide considered. 

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