Periodic table

The elements were organized by the professor of the University of St Petersburg, Dimitri Ivanovich Mendeleev, who wrote a book about the chemical elements, were about 63 elements, and Mendeleev organized them by function of the mass of their atoms establishing families and groups. The elements in the table are organized horizontally, in numerical sequence, according to their atomic numbers, and are organized through periods and families. There are seven periods in the table and the amount of electronic layers that the chemical elements present is indicated by the period number, they represent the horizontal rows of the table. 

References: Periodic table families. Link: http://www.tabelaperiodicacompleta.com/familias-da-tabela-periodica, 2017. Access on March 13, 2017.