To replicate the chemical space before 1869 and account for the role of atomic weights known in the 19th century, the researchers used the Reaxys chemistry database and, based on its extensive information, introduced an algorithm to adjust the chemical space to different sets of weights. Computational reconstruction of chemical space from atomic weights The systems they formulated were thus largely consistent with other periodic systems that would have been possible at the time, according to the computational analysis. Regarding the periodic systems of Lothar Meyer and Dmitri Mendeleev, both chemists could already rely on a mature chemical space and a quite stable set of atomic weights at that time. At the same time, the plethora of organic compounds obscured the identification of similarities between metals which are poorly represented in organic space." Wilmer Leal, doctoral student at the Max Planck Institute and the University of Leipzig, describes the essential role of organic chemistry in the formulation of the periodic system: "The rise of organic chemistry in the 1830s played a key role in facilitating the recognition of similarities between elements that are massively represented in chemical space, such as oxygen, hydrogen, carbon, nitrogen, and sulfur, and between metals often associated to organic compounds, such as sodium, potassium, palladium, platinum, barium, and calcium. Similarity among systems of chemical elements compared over time, with a strong stabilization of similarity evident after 1826. Between 18, the system continued to approach its basic structure, which was finally revealed in the 1860s. These discoveries persisted for years and provided consolidation of the chemical space and thus fairly stable periodic systems. In 1826, the discovery of elements slowed down, allowing chemists to further explore the properties of known substances and discover compounds that had new valences and thus new similarities among known chemical elements. The first quarter of the 19th century was characterized by a rapid discovery of chemical elements and their compounds, leading to an unstable period with a wide variety of periodic tables, only few of which stood the test of time. Their analysis of the knowledge of chemical space revealed, that the periodic table of chemical elements converged to a clearly visible basic structure as early as the 1840s, and was thus already encoded in space about two and a half decades before its formulation. So, we investigated in particular the chemical space between 18 to discover how well the periodic table corresponds to the chemical data at the time of its formulation," Guillermo Restrepo, Project leader at the Max Planck Institute for Mathematics in the Sciences describes the research team's objective.Įxpansion of the chemical space between 18 "We were attracted by the question of how the expansion of chemical space contributed to the formation of the first periodic systems. As knowledge of chemical substances grew throughout the history of science, so did potentially possible periodic systems, influenced by the state of the chemical space of the time. Order relationships were initially set up based on atomic weights and similarities in terms of commonality in chemical composition. The total combination of these two components forms the so-called chemical space. Periodic tables arose from the knowledge of the existing or potentially possible chemical elements and compounds known at that time. In a recently published article in the Proceedings of the National Academy of Sciences ( PNAS), the scientists look back to the beginnings of the periodic system, whose structure is characterized by similarity and order relationships among the elements.
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