The next period in the evolution of the periodic system began at the turn of the 20 th century, when chemical synthesis became the driving force for expanding the chemical space, which contributed to regularise the production of new chemicals by self-reinforcing the well established chemistry of the elements, where a few new valencies were discovered. This contrasts with what occurred by 1826, where new compounds made evident new combination capacities for already known elements . 1900 marks the beginning of a period of production of new chemicals supported by a stable chemical alphabet and with well-known grammar rules, which led the periodic system to further strengthening similarity ties among organogenic elements. Such a trend was interrupted by WW2, which enlarged the chemical alphabet and brought new chemistry to old elements, for instance F and lanthanoids, as motivated by war research. This led to a refinement of similarities among organogenic elements, as a consequence of combinations with new partners such as lanthanoids, and to the appearance of new stable families such as some of transition metals, the lanthanoids and the noble gases. 1980 entered chemistry into a new regime of production of chemicals , where new materials and organometallic chemistry added diversity to the chemical space, which led to the current periodic system where actinoids became a family supported by several compounds and further transition metal families were found.