Isotope relative abundance

Element Isotope Relative Abundance (%) Mass (Da) Isotope Relative Abundance (%) Mass (Da)... 

Elements Isotope Relative Abundance Isotope Relative Abundance Isotope Relative Abundance... 

Isotope Relative abundance (%) Mass (u) Calculated Measured... 

Isotope Relative abundances Percent molar abundance... 

Isotope Relative abundances Principal sources of nuclides ... 

Fig. 2. Hyperfine structure of Nd and Nd at ca. 1% dilution in lanthanum ethylsulphate (Bleaney and Scovil 1950). Each isotope (relative abundances 12% and 8%) gives (2/ + l)= lines, demonstrating that for each the nuclear spin / = J. From the overall widths of the structures, the ratio of the hyperfine splittings = 1.6087(10), in good agreement with the ratio 1.60860(36) for the atom from atomic beam measurements (Spalding 1963, Smith and Unsworth 1965).

Isotope l-s3- top [is- + Gk topos place] (1913) n. In chemistry, one of two or more forms of an element ( nuclides ) having the same number of protons in the nucleus but differing in mass number because of different numbers of neutrons. Natural elements are usually mixtures of isotopes thus the observed atomic weights are average values weighted by isotopic relative abundance. Serway RA, Faugh JS, Bennett CV (2005) College physics. Thomas, New York. 

Stable isotopes, relative abundance Mass number 107 109... 

RELATIVE ABUNDANCES OF NATURALLY OCCURRING ISOTOPES Table 4.18 Relative Abundances of Naturally Occurring Isotopes... 

Natural Isotopic Abundances. The relative abundances of natural isotopes produce peaks one or more mass units larger than the parent ion (Table 7.75a). For a compound C H O N, a formula allows one to calculate the percent of the heavy isotope contributions from a monoisotopic peak, Pto the Pm + 1 peak ... 

Compounds that contain chlorine, bromine, sulfur, or silicon are usually apparent from prominent peaks at masses 2, 4, 6, and so on, units larger than the nominal mass of the parent or fragment ion. Eor example, when one chlorine atom is present, the P + 2 mass peak will be about one-third the intensity of the parent peak. When one bromine atom is present, the P + 2 mass peak will be about the same intensity as the parent peak. The abundance of heavy isotopes is treated in terms of the binomial expansion (a -I- h) , where a is the relative abundance of the light isotope, b is the relative abundance of the heavy isotope, and m is the number of atoms of the particular element present in the molecule. If two bromine atoms are present, the binomial expansion is... 

Since detailed chemical structure information is not usually required from isotope ratio measurements, it is possible to vaporize samples by simply pyrolyzing them. For this purpose, the sample can be placed on a tungsten, rhenium, or platinum wire and heated strongly in vacuum by passing an electric current through the wire. This is thermal or surface ionization (TI). Alternatively, a small electric furnace can be used when removal of solvent from a dilute solution is desirable before vaporization of residual solute. Again, a wide variety of mass analyzers can be used to measure m/z values of atomic ions and their relative abundances. 

For other elements that occur with major relative abundances of more than one isotope in the natural state, the isotope pattern becomes much more complex. For example, with chlorine and bromine, the presence of these elements is clearly apparent from the isotopes Cl and for chlorine and Br and Br for bromine. Figure 47.2a shows the molecular ion region for the compound chlorodecane. Now, there are new situations in that C, C, C1, and Cl isotopes all have probabilities of occurring together. Thus, there are molecular ion peaks for + Cl, C + Cl, + Cl, and so on. Even so, the isotopic ratio of 3 1 for Cl to Cl is very clear... 

Isotope ratios are commonly reported as relative abundance (R), and comparison of two ratios (R, R2) represent the a-value (known as a fractionation factor). 

Trace-element analysis of metals can give indications of the geographic provenance of the material. Both emission spectroscopy (84) and activation analysis (85) have been used for this purpose. Another tool in provenance studies is the measurement of relative abundances of the lead isotopes (86,87). This technique is not restricted to metals, but can be used on any material that contains lead. Finally, for an object cast around a ceramic core, a sample of the core material can be used for thermoluminescence dating. 

The relative abundance of the stable isotopes of the PGMs and their CAS Registry Numbers are shown in Table 1. 

There are four stable isotopes of sulfur and S, which have relative abundances of 95.1, 0.74, 4.2, and 0.016%, respectively. The relative... 

Isotope Natural abundance (%) Nuclear spin Electric quadrupole moment NMR frequency fora 23.5 kO field (MHz) Relative sensitivity... 

This book presents a unified treatment of the chemistry of the elements. At present 112 elements are known, though not all occur in nature of the 92 elements from hydrogen to uranium all except technetium and promethium are found on earth and technetium has been detected in some stars. To these elements a further 20 have been added by artificial nuclear syntheses in the laboratory. Why are there only 90 elements in nature Why do they have their observed abundances and why do their individual isotopes occur with the particular relative abundances observed Indeed, we must also ask to what extent these isotopic abundances commonly vary in nature, thus causing variability in atomic weights and possibly jeopardizing the classical means of determining chemical composition and structure by chemical analysis. 

The relative abundances of the various isotopes of the light elements Li, Be and B therefore depend to some extent on which detailed model of the big bang is adopted, and experimentally determined abundances may in time permit conclusions to be drawn as to the relative importance of these processes as compared to x-process spallation reactions. 

Accurate atomic weight values do not automatically follow from precise measurements of relative atomic masses, however, since the relative abundance of the various isotopes must also be determined. That this can be a limiting factor is readily seen from Table 1.3 the value for praseodymium (which has only 1 stable naturally occurring isotope) has two more significant figures than the value for the neighbouring element cerium which has 4 such isotopes. In the twelve years since the first edition of this book was published the atomic weight values of no fewer than 55 elements have been improved, sometimes spectacularly, e.g. Ni from 58.69( 1) to 58.6934(2). 

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