User:Urayness/Oddo-Harkins rule

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Isotopic abundance

A plot of the isotopic compositions of the first 16 elements and their stable isotopes make up 99.9% of ordinary matter in the universe. Those isotopes with equal numbers of protons and neutrons [boxes] are particularly abundant.

The elemental basis of the Oddo-Harkins has direct roots in the isotopic compositions of the elements. While even atomic-numbered elements are more abundant than odd, the spirit of Oddo-Harkins extends to the most abundant isotopes as well. Isotopes containing an even number of protons (even atomic number) and an even number of neutrons are more abundant, including the most abundant isotope of iron, ⁵⁶Fe, with its 26 protons and 30 neutrons.  Isotopes having an equal number of protons and neutrons are the most abundant, however. These include ${\ce {^{4}_{2}He}}$, ${\ce {^{12}_{6}C}}$, ${\ce {^{14}_{7}N}}$, ${\ce {^{16}_{8}O}}$, ${\ce {^{20}_{10}Ne}}$, ${\ce {^{24}_{12}Mg}}$, ${\ce {^{28}_{14}Si}}$, and ${\ce {^{32}_{16}S}}$. Seven of the eight are alpha nuclides containing whole number multiples of He-4 nuclei (${\ce {^{14}_{7}N}}$ is the exception). Two of the eight ( ${\ce {^{4}_{2}He}}$ and ${\ce {^{16}_{8}O}}$) contain magic numbers of either protons or neutrons (2, 8, 20, 28, 50, 82, and 126) and are therefore predicted by the nuclear shell model to be unusually abundant. "That nuclei of this type are unusually abundant indicates that the excess stability must have played a part in the process of the creation of elements," stated Maria Goeppert Mayer in her acceptance lecture for the Nobel Prize in Physics in 1963 for discoveries concerning nuclear shell structure.