Chemists, Element Formation, and Stellar Energy

From about 1915, a new generation of scientists attempted to use the new physics to understand how elements were formed and why the stars shine. In this work, and especially with regard to the question of element formation, chemists played a role that for a period was as important as that played by physicists and astronomers. Several leading physical chemists, including Svante Arrhenius, Walther Nernst, Jean Perrin, and William Harkins, were interested in astronomy and cosmology and contributed to the new phase of astrochemistry. However, they worked individually and independently, and their research formed neither a recognized subdiscipline nor the nucleus of a scientific subcommunity. [21] 

In 1917 Harkins found that on the average elements of even atomic number (Z) are about 70 times as abundant in meteorites as those of odd Z he further noted that the first seven elements in the order of their abundance are all even-numbered and make up almost 99% of the material in meteorites. [28] Four years later he elaborated his assumption that the relative abundances of the atomic species of low atomic weight may be used as an index... of their relative stability. He now suggested several more rules, including that atoms with even A (mass number) and an odd number of electrons are extremely rare. [29] These rules were claimed to be valid for isotopes, and not merely elements. In 1931, after more data on the distribution of isotopes had been collected, he reported that even-A nuclei were much more frequent than odd-A nuclei. [30] 

Harkins s program of linking nuclear physics and geochemistry was not initially followed by other researchers, but it was not without impact and was often referred to in the 1920s. The program received support from Francis Aston s invention of the mass spectrometer, which was of great importance to geochemistry because it 

The group of chemists with an interest in astro- and geochemistry included also Gilbert Lewis, the famous American physical chemist. In an address of 1922 he discussed the cosmic origin of radioactive elements in a manner that, he admitted, may seem somewhat speculative in character. Like Nernst and Harkins, Lewis believed that not only had astronomy much to learn from chemistry, the latter science had also much to learn from astronomy. He argued as follows  

Weizsacker s theory shared with other theories of element formation the assumption of an equilibrium mechanism. It was the abandonment of this assumption in the 1940s that paved the way for the first successful big-bang model of the universe, proposed by George Gamow and his collaborators in 1948. That the equilibrium hypothesis might not be tenable had been suggested as early as 1931, when the two American chemists Harold Urey and Charles Bradley argued that the relative abundance of terrestrial elements could not be reconciled with the hypothesis, whatever the temperature of the equilibrium mixture. [45] 

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