Naturally occurring isotopes, relative

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

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). 

Elements with radioactive nuclides amongst their naturally occurring isotopes have a built-in time variation of the relative concentration of their isotopes and hence a continually... 

The occurrence of isotopes of some elements allows the presence of these elements to be readily identified in a mass spectrum of a compound. For example, Br has two naturally occurring isotopes with masses 79mu and 81 mu, in the relative... 

The relative atomic mass or the atomic weight as it is also often imprecisely termed is calculated as the weighted average of the naturally occurring isotopes of an element. [3]The weighted average is calculated from... 

All of the heteroatoms possess at least one naturally occurring isotope with a magnetic moment (Table 15). The nuclei 14N, 170 and 33S also possess an electric quadrupole moment which interacts with the electric field gradient at the nucleus, providing a very efficient mechanism for relaxing the nuclear spin. The consequence of this facilitation of relaxation is a broadening of the NMR signals so that line widths may be 50-1000 Hz or even wider. To some extent this problem is offset by the more extensive chemical shifts that are observed. The low natural abundances and/or sensitivities have necessitated the use of accumulation techniques for all of these heteroatoms. The relative availability of 170 and 15N enriched... 

There are three naturally occurring isotopes, 39K through 41K, of which 40K is radioactive with a half-life of 1.3 109 years. Tn ordinary potassium, this isotope represents only 0.0119% of the content. There are four other known isotopes, all radioactive. 33 K and 42K through 44K, all with relatively short half-lives measured in minutes and hours. In terms of abundance, potassium ranks seventh among the elements occurring in the earth s crust. In terms of content in seawater, the element ranks eighth, with an estimated 1,800,000 tons of potassium per cubic mile (388,000 metric tons per cubic kilometer) of seawater, First ionization potential 4,339 eV ... 

Uranium hexafluoride, UF6, shown here, is a relatively volatile molecular compound that is used in the separation of the naturally occurring isotopes uranium-235 and uranium-236. There is only one naturally occurring isotope of fluorine, so any difference in the molar mass of the molecule is due to the uranium. 

The following table lists the atomic masses and relative percent concentrations of naturally occurring isotopes of importance in mass spectrometry.1"5... 

Ans. The atomic masses indicated on the Periodic Table of the Elements are averages, but they are calculated relative to the mass of 12C. The mass number for iodine s naturally occurring isotope is 127, which is a total of the number of protons and neutrons, not true masses. 

The relative abundance of gold is 0.004 part per million (ppm) in Earth s crust. Deposits of the metal are found in South Africa, Siberia, North America, and South America. Gold has one naturally occurring isotope (197Au) and forty-five synthetic isotopes. 

Boron exists as two naturally occurring isotopes 1°B (10.01 u) and 1 lB (11.01 u). Calculate the relative abundance of each isotope of boron. 

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