Despite the key role of the chemical space in shaping the order and similarity relationships constituting the periodic system, only until recently the role of this space was taken into account to assess its interplay in the emergence of the periodic system . The expansion of the chemical space between 1800 and the time of the formulation of the system led the arrangement of order and similarities of the periodic system to converge to a backbone structure, ultimately unveiled in the 1860s. Nevertheless, such a convergence was not smooth but rather guided by two main transitions triggered by the discovery of elements and compounds revealing new forms of combinations of the chemical elements . This interplay between the chemical space and the periodic system opens the question for the current status of the system, given the exponential growth of the chemical space. Furthermore, the periodic system, formulated by Meyer and Mendeleev, has been adjusted but little modified to include new elements. Does that seemingly stable system still exist? To what extent has the rise of organometallic chemistry, materials science, and other areas affected its shape? Is the icon of chemistry affected by social, epistemic and technological changes such as wars, theories and the development of new chemical techniques? Those are questions we address in the current paper by computationally analysing Reaxys ® , 1 one of the largest databases of chemical information from the dawn of the nineteenth century up to date. The periodic system as provided by the chemical space Building up the periodic system for a given time in the evolution of the chemical space requires extracting order and similarity relationships among the chemical elements, out of the cumulative number of substances constituting the chemical space by the time of study (Fig. ). Nineteenth century was pervaded by atomic debates leading to different competing sets of atomic weights, which by 1860 boiled down to Cannizzaro's sets of weights, setting the stage for a long-sought standard set of atomic weights . The effect of the pre-1860 atomic weights upon the periodic system was explored in , where a high correlation was found among all those different sets of weights, including the ones currently in use. This produced largely similar order relationships between the elements, even from an early stage in history . The recognition of the relationship between atomic weight and atomic number led to take the latter as the ultimate ordering criterion for the chemical elements. This establishes an even more stable order relation among elements, which now depended not on real-valued measurements, that is atomic weight, but only on an integer-valued invariant descriptor for each element, namely atomic number .