The Origin of Isotopic Patterns

3 Calculation of Isotopic Patterns 12.3.1 The Origin of Isotopic Patterns 

Most of the chemical elements occur naturally not as a single species, but rather as a mixture of isotopes. The existence of isotopes was predicted already by de Marignac and discovered by Soddy in 1910 and Todd in 1912, respectively. Thomson found that neon forms isotopes with a mass of 20 and 22, when analyzing channel rays. Isotopes can be readily seen by means of a mass spectrometer, which 

Sir Joseph John Thomson, bom Dec. 18, 1856, in Cheetham HaU, England, died Aug. 30, 1940, in Cambridge. 

The analysis and interpretation of the isotopic pattern is a valuable tool to identify the nature and structure of molecules, in the mass spectrometer of course converted into gaseous ions, in particular for organic compounds. 

The accurate masses of the ions can be measured by means of precision mass spectrometry. For a variety of applications, it is sufficient to deal with nominal mass numbers. These are the integers close to the accurate masses. The natural abundances of the isotopes of carbon and chlorine are shown in Table 12.4. The abundances of the isotopes are given in % by mole, not in % by weight. 

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