The first period in the evolution of the periodic system -of setting up a basic chemical alphabet-spans the years before 1826, which covers the years of highest discovery rates ever of elements. In this period, the chemistry of the rather reactive halogens and of the recently discovered alkali and alkaline-earth metals kicks off leading to the recognition of the first similarities among chemical elements and to the emergence of the oldest families of the backbone of the periodic system. By 1826 the accelerated discovery of new elements by electrolysis and further reduction began to wind down , which constitutes the transition to the second phase in the evolution of the periodic system, where chemists enjoyed a rather stable set of elements that allowed for exploring their chemistries. This led to the recognition of some families of transition metals. Organic chemistry surged in this period, as facilitated by advances in analytical techniques . It is precisely the rise of organic chemistry what triggers the third phase in the evolution of the periodic system about 1860, when the semiotic capacity of the Berzelian notation -based on substance composition-saturated by the appearance of isomers . This prompted the emergence of molecular structural theory , which turned instrumental for a more controlled expansion of the organic chemistry side of the chemical space, supported by a growing synthetic activity, and by a well-established and professionalised chemistry practice with strong ties with the industry . The strong bias of the chemical space towards organic compounds challenged some of the similarities among elements previously supported by an important and diverse volume of inorganic compounds. This is especially evidenced in the appearance of a large family of organogenic compounds and, above all, in the relocation of H, which is not any more similar to alkali elements and becomes more similar to organogenic elements, a similarity it has kept ever since. The first decade of this period witnessed the formulation of the periodic system , a system whose essential features remained almost untouched until 1970 and that even today preserves about 80% of its similarities (Fig. ). To what extent this preservation, not observed for any previous periodic system (Fig. ) was important for the rise of the periodic system as the icon of chemistry?