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Alexandre-Emile Béguyer de Chancourtois
In 1862, Chancourtois invented the telluric screw, which was a three-dimensional arrangement of the elements, creating an early form of the periodic classification. The telluric screw plotted the atomic weights of the elements on the outside of a cylinder, so that one complete turnaround the cylinder corresponded to an atomic weight increase of 16. -
John Newlands
In 1865, Newlands noticed that there were similarities between elements with atomic weights that differed by seven. He called this ‘The Law of Octaves’, comparing them to the octaves in music. He did not leave any gaps for undiscovered elements in his table, and sometimes had to cram two elements into one box in order to keep the pattern. Because of this, the Chemical Society refused to publish his paper. -
Dmitri Mendeleev
In 1869, Mendeleev discovered and designed a periodic table based on atomic weights but arranged ‘periodically’, so when he put them in order of increasing atomic weight, certain types of elements regularly occurred. Elements with similar properties appeared underneath each other. He also left gaps for yet to be discovered elements. Mendeleev also predicted the properties of five undiscovered elements, and over the next decade when they were discovered, his predictions were proven to be correct. -
Julius Lothar Meyer
Meyer produced several Periodic Tables between 1864-1870. His first table contained just 28 elements, organised by their valency. In 1868 he incorporated the transition metals in a much more developed table which listed the elements in order of atomic weight, with elements with the same valency arranged in vertical lines. This table wasn’t published until 1870. He was also the first person to recognise trends in the properties of elements. -
William Ramsey
In 1894, William Ramsay discovered the noble gases and realised that they represented a new group in the periodic table. -
Henry Moseley
In 1914, Henry Moseley determined the atomic number of each of the known elements by using an x-ray gun to measure the wavelengths of x-rays given when fired at elements. He used the gun to calculate the frequency and realised if the elements were arranged in order of increasing atomic number rather than atomic weight, they gave a better fit within the periodic table. -
Glenn Seaborg
In 1940, Glenn Seaborg artificially produced heavy mass elements. These new elements were part of a new block of the periodic table that was called ‘actinides’.