The first person to try to organize the chemical elements into patterns was Johann Dobereiner. He grouped families of elements into triads in order of atomic mass in 1828. Elements were grouped into families because of the similarities in reaction types and in the formulas of compounds. The atomic mass of the middle member of the triad was close to the average of the atomic masses of the other two members. John Newlands arranged the elements into octaves in order of their atomic masses in 1863. He saw that every eighth element had similar chemical properties.
Dmitri Mendeleev created the first periodic table of the elements in 1868 by sorting cards depicting the individual elements known at that time. Mendeleev recognized that the properties of the elements were a periodic function of the atomic masses. He also recognized that the periods varied in length; he used periods of seven and seventeen elements. He also hypothesized that there were elements to be discovered to complete families so he created six blank spaces. Mendeleev put similar elements into columns; he placed Dobereiner’s triads into columns.
Over 700 versions of the periodic table of the elements have been proposed since Mendeleev’s first columnar table. A modern version of his periodic table updated by Glenn Seaborg in 1969 called the called the Extended Periodic Table appears in chemistry textbooks today. The Extended Periodic Table includes the man made elements. Seaborg also left spaces in his Extended Periodic Table for undiscovered elements. Another columnar form of the periodic table was proposed in 1928 by Charles Janet is the Left Step Periodic Table; it was updated to the ADOMAH Periodic Tablein 2006. The ADOMAH table is stacked to make it easier to write electron configurations.
Theodor Benfey proposed a two dimensional spiral table enfolding two islands in 1960. There is even a hexagonal spiral periodic table. John Clark proposed a spiral with oval outline in 1949 which inspired Philip Stewart to propose a three dimensional Chemical Galaxy periodic table in 2004. Pawel Najderek proposed a square-triangular periodic arrangement. Mohammed Abukar’s circular periodic table has been widely circulated. These geometrical forms of the periodic table still keep the elements in rows and families, but show the connectedness between both sides of the columnar periodic table now in current texts.
Timothy Stowe and Paul Giguere produced three dimensional periodic tables with axes based on the electron orbitals being filled. Their periodic tables of the elements are favored by physicists.
