The Development of the Periodic Table

If you asked most people (including most chemists) who discovered the periodic table, they would answer Dmitri Mendeleev, but it is worth noting that Mendeleev was not working in a vacuum and that his “discovery” was really the culmination of the work of many others.

Early Steps

As early as the late 1780’s Lavoisier was classifying and sorting elements by their properties (he used the groups gases, non-metals, metals and earths).


In 1829, Döbereiner found several “triads” - groups of three similar elements (such as chlorine, bromine and iodine, or lithium, sodium and potassium) where the properties of the middle element could be predicted from the other two.

Finding Patterns 

The periodic nature of elemental properties (the regular, repeating properties) was first demonstrated by Alexandre Béguyer de Chancourtois who created the “Telluric Screw”. This was a list of the elements written diagonally around a cylinder, so that a complete turn represented an increase in atomic mass of 16 (the difference between O and S). When written this way, a vertical line would run through elements with similar properties. 

In 1865, John Newlands presented a paper with an arrangement of elements similar to the table that Mendeleev would create 4 years later. Newlands’ arrangement was based on the idea of octaves - patterns in properties that repeated every seven elements (at the time the noble gases were unknown). There were short-comings in his arrangement, however. He failed to leave gaps for undiscovered elements and had to “cram” several elements into the same place to make the pattern work. Because of these issues, his work was rejected and his accomplishments were only recognized later in his life.





The consequences of timing 

Julius Meyer created an organized periodic table as early as1864 containing the first 28 elements. He continued to work on his table, including the transition metals by 1868 and finally publishing it in 1870 - a year after Mendeleev published his. Because he published second, his is not the name generally associated with the creation of the table, but he is now commonly acknowledged as the first person to recognize the true periodic nature of the elemental properties.





Mendeleev and the modern periodic table 

Dmitri Mendeleev was set to teach Chemistry in St. Petersburg, but couldn’t find a textbook he considered adequate. In the process of writing his own, he decided that he needed a way to organize the elements. By laying out cards with the elements and their properties and then moving them around, he found that by arranging the elements in order of atomic mass that certain properties repeated in consistent and predictable patterns.

Going even further, Mendeleev reversed the order of several elements where he felt the properties justified the change despite the atomic masses. For example, iodine and tellurium are in the “wrong” order by mass, but iodine is clearly much more like chlorine and bromine than tellurium is.

Mendeleev also left gaps in his table for “missing” elements and over the course of the next 15 years three of those elements were found with properties that very closely matched those predicted by Mendeleev.