Isotopic masses, table

Use of exact isotopic masses (Table 3.2) gives the accepted value for the atomic mass of chlorine ... 

These isotope masses and their ratio of abundances are characteristic of carbon. Similarly, the isotopes of other elements that occur naturally have fixed ratios of isotopes, as given in Tables 47.1 and 47.2 at the end of the accompanying full text. 

First, the percentages must be converted to fractions by dividing by 100%. Then we multiply these fractional abundances by the Isotopic masses and add the results. A table helps in organizing these manipulations ... 

Making and Using Tables Data Table 3 shows the isotopic mass and relative abundance for the most common isotopes of copper and zinc. 

The amounts of exchange and addition were calculated from a hydrogen isotope mass balance of the coal products, donor solvent and gas phase hydrogen. The starting and product weights of the coal and hydrogen compositions of the coal and coal products are shown in Table IV. From the values in Table IV, the net amount of hydrogen added to the coal, H, is... 

Note The nucleus of each element may have more than one neutron/proton ratio (different isotopes) in the table are presented the most abundant stable isotopes of some elements and the number before their symbols represents very approximately the mass of that isotope (mass number, A). 

Mass spectrometry is based upon the separation of charged ionic species by their mass-to-charge ratio, m/z. Within the general chemical context however, we are not used to taking into concern the isotopes of the elemental species involved in a reaction. The molecular mass of tribromomethane, CHBrs, would therefore be calculated to 252.73 g mol using the relative atomic masses of the elements as listed in most periodic tables. In mass spectrometry we have to leave this custom behind. Because the mass spectrometer does not separate by elements but by isotopic mass, there is no signal at m/z 252.73 in the mass spectmm of tribromomethane. Instead, major peaks are present at m/z 250, 252, 254 and 256 accompanied by some minor others. 

The isotopic mass is the exact mass of an isotope. It is very close to but not equal to the nominal mass of the isotope (Table 3.1). The only exception is the carbon isotope which has an isotopic mass of 12.000000 u. The unified atomic mass... 

Table A. 1 comprises the stable elements from hydrogen to bismuth with the radioactive elements technetium and promethium omitted. Natural variations in isotopic composition of some elements such as carbon or lead do not allow for more accurate values, a fact also reflected in the accuracy of their relative atomic mass. However, exact masses of the isotopes are not affected by varying abundances. The isotopic masses listed may differ up to some 10 u in other publications.

Table A.l. Isotopic mass, isotopic composition, and relative atomic mass [u] of non-radioactive elements. lUPAC 2001.

Instead of using the integers 37 and 35 as atomic masses, take the more precise atomic weights of the isotopes from Table 3-3 ... 

Groundwater-inflow rates as calculated by the solute and isotope mass-balance methods for several northern Wisconsin lakes are listed in Table I. Dissolved calcium was used as the solute tracer because it is the constituent whose concentration differs the most between groundwater and precipitation, the two input components to be separated by the method. In addition, calcium is nearly conservative in the soft-water, moderately acidic to cir-cum-neutral lakes in northern Wisconsin. Results from the two methods agree relatively well, except for Crystal Lake, where groundwater-flow reversals are frequent. 

ACTINIUM- [CAS 7440-34-8]. Chemical element symbol Ac. at. no. 89. at. wt. 227 (mass number of the most stable isotope), periodic table group 3, classed in the periodic system as a higher homologue of lanthanum. The electronic configuration for actinium is... 

RADON. [CAS 10043-92-2]. Chemical element symbol Rn, at. no. 86, at. wt. 222 (mass number of the most stable isotope), periodic table group 18 (inert gases), mp —71°C, bp —61.8°C. First ionization potential, 10.745 eV. Density 9.72 g/l O C, 760 torr), 7.5 x more dense than air. The gas has been liquefied at —65°C and solidified at —110°C. Radon was first isolated by Ramsay and Gray in 1908. Prior to acceptance of the present designation, radon was called niton or radium emanation. See also Radioactivity. 

Because the mass of an atom s electrons is negligible compared with the mass of its protons and neutrons, defining 1 amu as 1/12 the mass of a atom means that protons and neutrons each have a mass of almost exactly 1 amu (Table 2.1). Thus, the mass of an atom in atomic mass units—called the atom s isotopic mass—is numerically close to the atom s mass number. A jH atom, for instance, has a mass of 1.007 825 amu a 292U atom has a mass of 235.043 924 amu and so forth. 

Naturally occurring boron consists of two isotopes 10B (19.9%) with an isotopic mass of 10.0129 amu and nB (80.1%) with an isotopic mass of 11.009 31 amu. What is the atomic mass of boron Check your answer by looking at a periodic table. 

Table 2.1 Isotopes of arsenic (Audi et al., 2003 Holden, 2007 Lindstrom, Blaauw and Fleming, 2003).15As is the only stable arsenic isotope. The possible decay modes include electron capture (EC), electron emission (P ), positron emission (P+), proton decay (p), internal transition (IT), and neutron emission (ne). Superscripts on some of the arsenic isotope mass numbers designate excited-state isomers. The first (lowest energy) excited state is designated with an m and a second excited state is designated with an n. ...

Isotopes are designated by their mass numbers. The isotopes in Table 14.1 are called H-l, H-2, and H-3. The various isotopes of any element are naturally occurring, although other isotopes can be produced synthetically. In hydrogen, more than 90 percent of the atoms are the H-l isotope. 

In section 5.1, you learned how to use isotopic abundances and isotopic masses to find the average atomic mass of an element. You can use the average atomic mass, found in the periodic table, to describe the average mass of an atom in a large sample. 

Most elements appear in nature as isotope mixtures. Thus, natural carbon is a mixture of 98.90 % of isotope 12C and 1.10 % of isotope 13C. Table 6.1 lists the abundances of a few elements that are important in organic chemistry. In Appendix 4, the masses and the isotopic abundances are given for all the isotopes except the rare earths. 

I Atomic mass and mass number are not the same. Atomic mass refers to the naturally occurring mixture of isotopes mass number refers to an individual isotope. Atomic mass is an average and is never an exact integer mass number is a sum (of the number of protons plus the number of neutrons) and is always an integer. Except for the artificial elements, mass numbers are not given in the periodic table. 

Chromium has the atomic number 24. Of the 13 known isotopes (mass numbers 45-57), four are stable, giving chrominm the relative atomic mass 51.9961 ( C = 12.0000). Table 1 lists the properties of some isotopes. Cr may be used for NMR spectroscopy however, its relative receptivity (8.62 x 10 , H= 1.00), quadmpole moment (4.1 x 10 ° m ), and low resonance frequency (16.956MHz, H = 300MHz) pose experimental difficulties. Radioactive Cr is used in medical tracer studies. 

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