Isotopes of naturally occurring

ISOTOPES OF NATURALLY OCCURRING ELEMENTS AND THEIR ABUNDANCES... 

What are the most common and least common isotopes of naturally occurring lead How many atoms of are there for every atom of... 

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

Atoms of many other elements contain nuclei that have different numbers of neutrons. For example, carbon (Z = 6) can have six neutrons (M = 6 + 6 = 12), seven neutrons (M = 13), or eight neutrons (M = 14). Atoms of the same atomic number but having different numbers of neutrons (and different atomic masses) are called isotopes. Thus, naturally occurring carbon has three isotopes, for which Z = P = 6 and N = 6 or 7 or 8. These are written. ... 

Table 21.1 summarizes a number of properties of these elements. The difficulties in attaining high purity has led to frequent revision of the estimates of several of these properties. Each element has a number of naturally occurring isotopes and, in the case of zirconium and hafnium, the least abundant of these is radioactive, though with a very long half-life ( Zr, 2.76%, 3.6 x 10 y Hf, 0.162%, 2.0 X 10 5 y). 

Table 27.1 lists some of the important atomic and physical properties of these three elements. The prevalence of naturally occurring isotopes in this triad limits the precision of their quoted atomic weights, though the value for Ni was improved by more than two orders of magnitude in 1989... 

Our discussion concentrates on the uranium-235 isotope. It makes up only about 0.7% of naturally occurring uranium. The more abundant isotope, uranium-238, does not undergo fission. The first process used to separate these isotopes, and until recently the only one available, was that of gaseous effusion (Chapter 5). The volatile compound uranium hexafluoride, UF6, which sublimes at 56°C, is used for this purpose. 

Rn. a radioactive isotope of radon, is a decay product of naturally occurring uranium-238. Because it is gaseous and chemically... 

The atomic weight increases regularly across the row except for the inversion at cobalt and nickel. We would expect the atomic weight of Ni to be higher than that of Co because there are more protons (28) in the Ni nucleus than in the Co nucleus (27). The reason for the inversion lies in the distribution of naturally occurring isotopes. Natural cobalt consists entirely of the isotope 2 Co natural nickel consists primarily of the isotopes Ni and Ni, the 58-isotope being about three times as abundant as the 60-isotope. 

E.35 A mass spectrum of Br2 has three peaks, with the mass numbers 158, 160, and 162. (a) Use this information to determine which isotopes of bromine occur in nature, (b) If the relative heights of the peaks, which depend on abundance, are 33.8, 33.3. and 32.9. respectively, which isotope is more abundant ... 

C22-0019. Calculate the isotopic abundances of naturally occurring uranium 10 years ago. 

Ans. Hydrogen occurs as diatomic molecules, and it would be easy to separate H , H H, and 2H , but not the individual atoms. But there would be relatively little "H, since in abundance the heavy isotope accounts for only 0.015% of naturally occurring hydrogen atoms. 

There are four such scries of naturally occurring isotopes. The series in which all mass numbers are evenly divisible by 4 is called the 4/i series. The scries with mass numbers 1 more than the corresponding 4/i series members is called the 4n + 1 series. Similarly, there are a 4n + 2 series and a "4/i + 3 series." Since the mass numbers change by 4 or 0, no member of any series can produce a product in a different scries. 

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