SCIENCE: HISTORY OF PERIODIC TABLE

• By the middle of the 19th century, about 60 elements had been discovered
• 1862 - French geologist Alexandre-Emile Béguyer de Chancourtois plotted the atomic weights of elements on paper tape and wound them, spiral-like, around a cylinder. The design put similar elements onto corresponding points above and below one another. He called his model the telluric helix or screw.
• 1864 English chemist John Newlands noticed that, if the elements were arranged in order of atomic weight, there was a periodic similarity in every 7 elements. He proposed his 'law of octaves' similar to the octaves of music. Noble gases had yet to be discovered, which is why Newland's table had a periodicity of 7 rather than 8.
• 1868 Lothar Meyer compiled a periodic table of 56 elements based on a regular repeating pattern of physical properties such as molar volume. Once again, the elements were arranged in order of increasing atomic weights. (Meyer's work was not published until 1870.)
• 1869 Russian chemist Dmitri Mendeleev produced a periodic table based on atomic weights but arranged 'periodically'. Elements with similar properties appeared under each other Gaps were left for yet-to-be-discovered elements
• 1894 William Ramsay discovered the noble gases and realized that they represented a new group in the periodic table. The noble gases added further proof to the accuracy of Mendeleev's table.
• 1913 Henry Moseley determined the atomic number of each of the known elements. He realized that, if the elements were arranged in order of increasing atomic number rather than atomic weight, they gave a better fit within the 'periodic table
• 1928 Amateur French scientist Charles Janet uses mathematical patterns to investigate the electron configuration of elements He groups elements into blocks named after their atomic orbitals: s-block (sharp), p-block (principal), d-block (diffuse), and f-block (fundamental).
• 1944 Glenn Seaborg proposed an 'actinide hypothesis' and publis his version of the table in 1945. The lanthanide and actinide series form the two rows under the periodic table of elements