-
Johann Dobereiner proposes the Law of Triads
The middle element in the triad has atomic weight that is the average of the other two members. -
Alexandre Beguyer de Chancourtois publishes a list of all the known elements
The list was constructed as a helical graph wrapped around a cylinder-elements with similar properties occupied positions on the same vertical line of cylinder (the list also included some ions and compounds). -
John Newlands writes a paper proposing The Law of Octaves
Elements exhibit similar behavior to the eighth element following it in the table. -
Dimitri Mendeleev proposes arranging elements by atomic weights and properties
Mendeleev's periodic table contained 17 columns with two partial periods of seven elements each followed by two nearly complete periods. -
Henry Moseley derives the relationship between x-ray frequency and the number of protons in elements
Through this he arranged the elements according to increasing atomic numbers and not atomic masses and subsequently some of the inconsistencies associated with Mendeleev's table were eliminated. -
Glenn Seaborg discovers the transuranium elements and reconfingures the periodic table
He did so placing the lanthanide/actinide series at the bottom of the table.
