In 1817 Johann Dobereiner discovered that the atomic weight of strontium was midway between the calcium and barium, and these possessed similar chemical properties. In 1829, after discovering the halogen triad of chlorine, bromine, and iodine and the alkali metal triad of lithium, sodium and potassium, he proposed Law of Triads for which the middle element of three (ordered by the atomic weight) had properties which were the average of the other two.
In 1863, the French geologist, A. E. Béguyer de Chancourtois created a list of the elements arranged by increasing atomic weight. The list was wrapped around a cylinder so that several sets of similar elements lined up. In England, the analytical chemist John A. R. Newlands also wrapped elements and developed the octave rule, noting chemical groups repeated every eight elements, but his work was ignored for years.
Chemists Dmitrii I. Mendeleev (Russia), and Lothar Meyer (Germany) were working independently in 1868 and 1869 on similar table of elements grouped into seven columns according to chemical and physical properties.
In 1870 Meyer's table and periodic law was published, an accurate accounting of the then known facts about each element, which clearly indicated the existence of periodic chemical families, but focused on physical properties. A year earler in 1869, Mendeleev presented a bolder and scientifically more useful table, which focused on chemical properties. His paper, "On the Relation of the Properties to the Atomic Weights of the Elements," demonstrated the periodic relationship between chemical groups (elements with a similar stoichiometry of reaction) noting "...if all the elements be arranged in order of their atomic weights a periodic repetition of properties is obtained." It was further validified when gaps in the table accurately predicted undiscovered elements.
William Ramsay produced a more modern table that was similar to a later table by Meyer and arranged, as was Mendeleyev's, according to atomic weight, but with Group 0. This endeavor was stimulated in 1895 by Lord Rayleigh's discovery of the inert gaseous element argon, which did not fit into a known periodic group. In 1898, Ramsey suggested it be placed between chlorine and potassium in a family with helium. It was called the 0 group due to the zero valency. With this, Ramsey predicted the properties of neon.
In 1913, the table was reordered by Henry Mosely according to atomic numbers (nuclear charge) rather than by weight. The extension of the Periodic Law continued into the present with the creation of artificially produced, short lived elements of atom smashers and supercolliders of high energy physics. Harry D. Hubbard's (National Bureau of Standards) Periodic Chart of the Atoms, brought the table to date in 1924. In the 1930s Glenn Seaborg (working with Fermi) removed the heaviest elements from body of the table and named them the Actinide series. This permitted proper placement of the subsequently created Transactinide elements.
In 1994 Roy Alexander designed and patented the "Alexander Arrangement of the Elements", a three-dimensional periodic chart integrating the separate Lanthanide and Actinide series by using all three dimensions. This arrangement also permitted location of all the element data blocks in a continuous sequence according to atomic numbers while retaining property interrelationships.
This eased the use & understanding of the periodic chart.