The six stages of the convergence of the periodic system to its final structure

The periodic system encodes order and similarity among chemical elements arising from known substances at a given time that constitute the chemical space. Although the system has incorporated new elements, the connection with the remaining space is still to be analysed, which leads to the question of how the exponentially growing space has affected the periodic system. Here we show, by analysing the space between 1800 and 2021, that the system has converged towards its current stable structure through six stages, respectively characterised by the finding of elements (1800-1826), the emergence of the core structure of the system (1826-1860), its organic chemistry bias (1860-1900) and its further stabilisation (1900-1948), World War 2 new chemistry (1948-1980) and the system final stabilisation (1980-). Given the self-reinforced low diversity of the space and the limited chemical possibilities of the elements to be synthesised, we hypothesise that the periodic system will remain largely untouched. The periodic system was formulated in the 1860s by analysing order and similarities among chemical elements, but it is unclear how the exponentially growing chemical space has affected the periodic system. Here, evolution of the chemical space between 1800 and 2021 is analyzed, and it is shown that the system converged towards its current stable structure through six historical stages.