Nuclide Masses

Nuclide masses are ordinarily tabulated using units of grams per mole. Therefore, to compute HE, it is useful to rewrite Equation with energy in units of kilojoules per mole and the change in mass in grams per mole ... 

This graph and Fig. 26-6 are almost the inverse of one another, with the maxima of one being the minima of the other. Actual nuclidic mass is often a number slightly less than the number of nucleons (mass number). This difference divided by the number of nucleons (packing fraction) is proportional to the negative of the mass defect per nucleon. 

Atomic number 87, atomic relative mass 223.019731 (nuclidic mass of the longest half life isotope). 

From the nuclidic mass Be (9.0154) and Li (6.01702), the energy released in MeVcalculated compared with the energy released in carbon cycle (30 MeV) and in solar-hydrogen cycle (26.6MeV). ( He = 4.0015 iH = 1.00728)... 

A unique molecular formula (or fragment formula) can often be derived from a sufficiently accurate mass measurement alone (high-resolution mass spectrometry). This is possible because the nuclide masses are not integers (see Table 2.2). For example, we can distinguish at a unit mass of 28 among CO, N2, CH2N, and C2H4. 

The ultra-high mass resolution capabilities of FTMS will also be used in the future for accurate determination of nuclide masses. It is possible that all the known stable nuclides will have their masses reexamined by FTMS. A recent example of this type of measurement is the determination of the difference in mass between 3He+ and 3H+ by FTMS (99), which may be used in conjunction with... 

The term atomic mass will be understood to mean average atomic mass nuclidic mass refers to one particular isotope of an element. Atomic masses are used in nearly all chemical calculations. 

Table 2-1. Some Nuclidic Masses in Atomic Mass Units...

Nuclidic mass = mass of a particular nuclide, relative to mass of 12C, exactly 12 u. Atomic masses, Ar, commonly... 

A mass spectrometer is an instrument that separates particles by mass and measures their individual relative masses. If a nuclidic mass of an unknown compound is known with great precision from mass spectrometry, the exact molecular formula can often be deduced directly from this information without resort to a quantitative chemical analysis. 

When these nuclidic masses are compared with the experimental value, 44.025 u, C2H40 is the only formula that fits the data within the claimed precision so this must be the formula of the compound. 

It has been found by mass spectrometric analysis that in nature the relative abundances of the various isotopic atoms of silicon are 92.23% 28Si, 4.67% 29Si, and 3.10% 30Si. Calculate the atomic mass of silicon from this information and from the nuclidic masses. 

The atomic mass is the average of the three nuclides, each weighted according to its own relative abundance. The nuclidic masses are given in Table 2-1. 

Naturally occurring boron consists of 80.22% nB (nuclidic mass = 11.009) and 19.78% of another isotope. To account for the atomic mass, 10.810, what must be the nuclidic mass of the other isotope ... 

The nuclidic mass of 90Sr had been determined on the old physical scale (160 = 16.0000) as 89.936. Calculate the mass of 90Sr to the atomic mass scale on which 160 is 15.9949. 

EXAMPLE 1 Consider the three gases CO, C2H4, and N2. Since 12C, 160,14N, and 111 dominate over all other isotopes, the mass spectrometer will reveal the presence of a particle of approximate mass 28 in all three cases. If the measurements are made with great precision, the three gases can easily be distinguished on the basis of their nuclidic masses, which are calculated below. 

Note The observed value for XH is 0.06 percent lower because of the reduced mass effect. In accordance with a refinement of the simple Bohr theory, R increases with increasing nuclidic mass toward a maximum of 109,737 cm-1. The predicted radii of the orbits are... 

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