DEVELOPING THE PERIODIC TABLE

The history of the Periodic Table only goes back to the early 1800’s.The development of the Periodic Table of the Elements fundamentally changed the process of discovering new elements.   It’s “invention” allowed scientists a new way to predict new elements and to develop a pattern or periodic reoccurrence of their properties.  This “periodic reoccurrence” is why the table is referred to as the “Periodic Table.” 

By 1815 there were 45 elements that were identified.  Chemists were just beginning to realize that there may be a pattern to finding more elements.   Johann Dobereiner (1780-1849), a German chemist in 1817 started to see groupings of 3.  He claimed that calcium, strontium and barium had similar properties as did chlorine, bromine, and iodine.  He proposed a Law of Triads in 1829 which states that the atomic weight of the second element would fall half of the first and second element.   A pattern was emerging, but not enough elements were discovered with these properties to “see” a periodically repeating pattern of elements with similar characteristics.  Other scientists were also working on discovering relationships between the elements, but accurate values of what was referred to as the atomic weight prevented them from seeing an overall relationship.

A. Béguyer de Chancourtois. Reproduced courtesy of Annales des mines, Paris.

The first attempt of a table is attributed to a French geologist Alexandre Beguyer de Chancourtois (1820-1886). He proposed a chart that used atomic weight to order the elements. In the 1800’s scientists were just getting to understand that the Earth is made of elements.    He started looking for a relationship of the known elements and developed a mathematical relationship of properties of the known to discover the unknown elements.    He created a continuous spiral that was divided into 16 parts, so all elements could be compared to oxygen whose atomic weight was considered 16.  This became the standard of which other elements were measured. However, this did not work as he included also ions and compounds in his chart, but he developed the idea that increasing atomic weight of elements could predict properties.