Given the relationship between the chemical space and the periodic system, changes and regularities in the former affect the evolution of the latter. Thus, the periodic system is influenced by patterns in the way chemists practice their science over history, which involves the surge of trendy research topics that are in turn influenced by groundbreaking theories, techniques, and even by sociopolitical events such as World Wars (WWs). Instances of these influences include the early 19 th century use of electrolysis to discover elements and the shifting from inorganic to organic chemistry ; the incorporation of molecular structural theory by mid 19 th century ; the professionalisation of chemistry and the strong academic-industrial relationship initiated in the same century ; the preponderance of synthesis over extraction to expand the chemical space at the turn of the 20 th century ; the advent of big science by WW2 times , with the discovery of most of the actinoids, the rise of the chemistry of some elements such as Si and the rediscovery of others such as F and lanthanoids; and in more recent times the emphasis on organometallic chemistry and material sciences . Several of these events have actually demarcated the evolution of the periodic system as observed in the six periods we found for the historical unfolding of the periodic system. These periods result from patterns in the degree of preservation of periodic systems of the past into their respective futures. We quantified such a preservation by determining the historical duration of families of similar elements across time.