Oddo-Harkins rule

The second rule is the so-called Oddo-Harkins rule, which states that nuclides of even atomic numbers are more abundant than those with odd numbers. As shown in Table 1.1, the most common of the four possible combinations is even-even and the least common is odd-odd. 

Figure 9.3 The relative abundance of the rare earth elements according to Goldschmidt and Thomassen (above) and Ida Noddack (below[57]). The Noddacks found a much higher abundance of neodymium than the Norwegian researchers, but their data were not generally accepted. Both diagrams illustrate the Oddo-Harkins rule very clearly.

Harkins s rule of the dissymmetry between even-odd nuclei is sometimes referred to as the Oddo-Harkins rule. In 1914 the Italian chemist Guiseppe Oddo suggested that elements with atomic weights a multiple of... 

It is also seen from Table 11.17 the crustal content of even-numbered elements is consistently higher than for odd-numbered elements. This observation is consistently higher than for the Oddo-Harkins rule according to which nuclei with equal numbers of protons and neutrons are inherently more stable than those which have an unpaired proton or neutron. 

The abundances are a consequence of how the elements were synthesized by atomic fusion in the cores of stars with heavy elements only made in supernovae. Synthesis of heavier nuclei requires higher temperature and pressures and so gets progressively harder as the atomic number increases. The odd/even alternation (often referred to as the Oddo-Harkins rule) is again general, and reflects the facts that elements with odd mass numbers have larger nuclear capture cross sections and are more likely to take up another neutron, so elements with odd atomic number (and hence odd mass number) are less common than those with even mass number. Even-atomic-number nuclei are more stable when formed. 

Figure 6 Solar system abundances by mass number. Atoms with even masses are more abundant than those with odd masses (Oddo-Harkins rule) (source Palme and Beer, 1993).

It is observed that the abundance decreases with increasing atomic number Z HREEs are much less abundant than LREEs. What s more, according to the Oddo-Harkins Rule, elements with an even atomic number are more abundant than elements with an odd atomic number. For instance, cerium (Z = 58) is more abundant than lanthanum (Z = 57) and praseodymium (Z = 59). Cerium is the dominating rare earth in the LREE, whereas Y is the dominant rare earth in the HREE (Binnemans et al. 2013). 

The Oddo—Harkins rule states that elements with an even atomic number (such as carbon) are more common than elements with an odd atomic number (such as nitrogen). Reference Wikipedia, https //en.wikipedia.org/wiki/Oddo-Harkins rule See also Oddo (1914) and Harkins (1917). 

Furthermore, the abundances of LREE and HREE are not similar. The LREEs are much more common. And within the lanthanide series, due to the Oddo-Harkins rule (see Chap. 3), the REEs with an even atomic number are more common than the REEs with an odd atomic number. In a chart of the abundance, this is clearly visible as a saw tooth pattern (Chap. 1, Fig. 1.3). 

The rare earth minerals always contain a variety of rare earth elements. The study of the elemental distribution of rare earths in minerals and roeks has been a subject of geochemistry and mineral chemistry for many years. Their distribution basically follows the Oddo-Harkins rule (Oddo 1914, Harkins 1917) i.e., a lanthanide with even atomic number is more abundant than the neighboring lanthanides with odd atomic number in natural minerals. From the view point of the distribution of rare... 

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