Our results also shed light on current discussions about the periodic system. For instance, the "correct" position some elements should have in the periodic system, as is the case of H . Our work demonstrates that such discussions must be framed in a historical context. Before mid 19 th century, H was akin to alkali elements, however, once organic chemistry took the lead of the chemical space, H became similar to the halogens. Other discussions spin around the right constitution of group 3, with possible but excluding options: {Sc, Y, La, Ac} or {Sc, Y, Lu, Lr}. Such group-3 question even led to the creation of an IUPAC group to analyse the case and to provide a recommendation . Our results indicate that there has been no moment in history depicting any of the options. Chemical space shows a rather stable family of similar elements gathering together Sc, Y and the lanthanoids, from La to Lu, which has been well-known as rare earths for more than a century . These results indicate the potential use of our methods to avoid lengthy discussions, which can be easily solved by analysing the current and historical status of the chemical space and its emergent periodic system. Furthermore, our results indicate that the evolution of the periodic system has been mainly affected by two sorts of perturbations, namely by changes in the number of elements and by diversification of the chemistry of the elements. The former occurred, for instance, between 1800 and 1826, when the rapid discovery of elements perturbed the few similarities existing among older elements. A similar situation came about with the discovery of actinoids during WW2. Chemistry diversification, in turn, corresponds to the exploration of new facets of the chemical behaviour of formerly known elements. This is exemplified by the transition of H from the alkali to the organogenic elements, which occurred due to the competing inorganic and organic chemistries of H that the rise of organic chemistry tilted towards its side, as a consequence of the large volume of diverse organic chemical compounds that surpassed the diversity of its inorganic counterparts. We assess diversity in terms of the number of chemical formulas. Hence, the surge of organic chemistry was accompanied by a surge of formulas, which often combined H, C, N and O in different proportions. Inorganic chemistry could not compete with such a diversity and H weakened its "inorganic" similarities. A further instance of perturbations through chemistry diversification is the case of F, whose vertiginous rise in number of diverse organic compounds around 1960 led to the splitting of the large family of organogenic elements, mainly by the strengthening of similarities among halogens.