De Chancourtois's Helical Periodic Table
06th Mar 2020 @ 3 min read
The De Chancourtois periodic table was the first periodic table in which elements were arranged in the increasing order of atomic weights. Unlike others, it is a three-dimensional cylinder. The ordering of the elements starts from the top with zero atomic weights. The first element in the table is hydrogen, the lightest of all, which is followed by lithium, beryllium, boron, carbon, nitrogen, oxygen, and so on. From the top to bottom, the atomic weights of elements increases.
The figure below shows the unrolled De Chancourtois periodic table on the left and rolled, a cylinder, on the right.
De Chancourtois divided the circumference of the cylinder into 16 units. Consequently, the helical curve completes its first circle (or revolution) at 16 units, which is the atomic weight of the oxygen. The second circle completes at 32 units, the atomic weight of sulfur, and the third at 48 units, which is titanium. In the above table, the elements are limited up to calcium; so, any elements after 40 including titanium is not in it. The uncut table is mentioned at the end of this article.
Note: In the above table, atomic weights are expressed in integers, which is not true.
Periodicity
The notion of periodicity was first seen in the de Chancourtois table. The helical curve repeats itself at a multiple of 16. Thus, every 17th element is positioned directly below the 1st. For example, lithium, sodium, and potassium are vertically aligned. They share similar chemical properties. He observed that the properties of elements are repeated at a regular interval of atomic weights. In other words, the properties of elements are the periodic function of their atomic weights.
History
Alexandre-Emile Beguyer de Chancourtois was a French geologist and mineralogist. He proposed his periodic system in 1862, three years before Newlands' law of octaves, and published his work in Comptes rendus, a French scientific journal. Unfortunately, his work did not get much attention. The main reason was the diagram, which clearly shows the periodicity of elements, was omitted from his publication. Though the diagram showed up later in his geology article, it remained unnoticeable by chemists. His contribution was recognized in scientific communities after a lecture by Dmitri Mendeleev in 1869.
De Chancourtois called his diagram as vis tellurique. It means a telluric spiral. Telluric because tellurium comes in the middle of the cylinder (see the table below).
Entire Table
The complete table of de Chancourtois is presented below.
The previous table does not concur with the modern periodic table. The atomic weights are several elements are highly inaccurate. Also, there are many missing entries that suggest the existence of undiscovered elements at that time. The original table of de Chancourtois can be downloaded from here.
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