Things are different from each other, and each can be reduced to very small parts of itself.|
- Ancient knowledge
"The chemical elements are composed of... indivisible particles of matter, called atoms... atoms of the same element are identical in all respects, particularly weight." - Dalton "...if all the elements be arranged in order of their atomic weights a periodic repetition of properties is obtained." - Mendeleyev Around 400BC it was noticed by Greek philosophers realized that they used the words "element', and `atom' to describe the smallest parts of matter and their differences. These ideas survived for 2000 years. Concepts of Earth, Wind, Fire and Water were learned and studied.
Much later, Boyle, a Greek scientist, lent important weight to the atomic theory of matter in the 1600s. It was Lavoisier who divided the few elements known in the 1700's into four classes, and then John Dalton made atoms even more convincing, suggesting that the mass of an atom was it's most important property. In the early 1800's Dobereiner noted that similar elements often had relative atomic masses, and DeChancourtois made a cylindrical table of elements to display the periodic reoccurrence of properties. Cannizaro determined atomic weights for the 60 or so elements known in the 1860s, then Newlands arranged a table with the elements giving a serial number in order of their atomic weights, beginning with Hydrogen. This made evident that "the eighth element, starting from a given one, is a kind of repetition of the first", which Newlands called the Law of Octaves. Both Meyer and Mendeleyev constructed periodic tables independently, Meyer more impressed by the periodicity of physical properties, while Mendeleyev was more interested in the chemical properties. Mendeleyev published his periodic table & law in 1869 and forecast the properties of missing elements, and chemists began to appreciate it when the discovery of elements predicted by the table took place. Periodic table has always been related to the way scientists thought about the shape and structure of the atom, and has changed accordingly. The 'modern' periodic table is very much like a later table by Meyer, arranged, as was Mendeleyev's, according to the size of the atomic weight, but with Group 0 added by Ramsay. Later, the table was reordered by Mosely according to atomic numbers (nuclear charge) rather than by weight. The Periodic Law revealed important analogies among the 94 naturally occurring elements, and stimulated renewed interest in Inorganic Chemistry in the nineteenth century which has carried into the present with the creation of artificially produced, short lived elements of "atom smashers" and supercolliders of high energy physics. Harry D. Hubbard, of the United States National Bureau of Standards, modernized Mendeleyev's periodic table, and his first work was published in 1924. This was known as the Periodic Chart of the Atoms. Into the 1930s the heaviest elements were being put up in the body of the periodic table. Glenn Seaborg "plucked those out" while working with Fermi in Chicago, naming them the Actinide series, which later permitted proper placement of subsequently "created" elements - the Transactinides, changing the periodic table, yet again. These elements were shown separate from the main body of the table.