In addition, to explore the evolving qualitative features of periodic systems (Fig. ), families of similar elements were automatically detected using computer vision techniques (Methods 6.7). Figure : Computational approach to analyse the evolution of the periodic system. a, Chemical space expands at an exponential rate and its number and diversity of substances may affect the structure of the periodic system. This is here represented as possible periodic systems for different periods in history. b, Calculation of element similarity as based on molecular formulas of the chemical space from which templates R-X n are derived (Methods 6.2). The similarity of any two elements depends on their common number of templates (co-occurrence matrix). Self-similarity is defined as the number of templates of an element contributing to similarity with other elements. c, Calculation of similarities among periodic systems leading to explore the evolution of the periodic system as well as of its families of similar elements.