Mendeleevs Attempted System

FIGURE 3 Dmitrii Ivanovich Mendeleev (1834-1907). Photo and permission from Edgar Fahs Smith Collection. 

FIGURE 4 An attempted system of the elements based on their atomic weight and chemical analogies. A pamphlet with Mendeleev s first periodic system, distributed on February 17,1869. 

If Mendeleev was to convince the chemical community of the fimda-mental character of his system, he had to explain his line of thoughts in more detail. Indeed, his pamphlet did not contain any evidence that might persuade other chemists of the validity of his assertions (Brooks, 2002). Over the course of the next two years (1869-1871), Mendeleev 

Mendeleev thus began by investigating the atomic volumes of the elements as a possible periodic function of the atomic weight, hoping that his research would confirm the periodic law. His research on the atomic volumes of the elements illustrated that this physical property tended to rise in each short period, reaching a maximum value in the halogens and alkali 

Due to the recent discoveries of the rare-earth elements, most of their chemical and physical properties were not yet known in 1869, and Mendeleev had to manage with the limited information that was available at that time. As a consequence, Mendeleev did not succeed in correctly accommodating these elements when he constructed his Attempted System. This is not surprising given the fact that Mendeleev still adhered 

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On February 17, 1869 (according to the old Julian calendar), the Russian chemist Dmitrii Ivanovich Mendeleev (1834 1907, Figure 3) wrote a pamphlet entitled "An Attempted System of the Elements Based on... 

For example, lanthanum was allotted an atomic weight of 94 (AWi) in Mendeleev s Attempted System. The modem value for lanthanum s atomic weight is 138.9 AW and as all the rare-earth elements typically exhibit the +III oxidation state, its modern valency is 3 (1 2). With the aid of Eq. (7), the valency number Vi as used by Mendeleev in the beginning of 1869 can be established ... 

Mendeleev had been working on the optimization of fhe periodic law for quite some time now. He had always preferred the long form table (i.e., his Attempted System), but in November 1870, Mendeleev created a short form table, his Natural System of the Elements (Figure 5) (Mendeleev, 1871 Mendelejeff, 1870). In a long form of the periodic table, the d-block elements are separated from the main group elements, whereas this is... 

Mendeleev, D.I., 1869a. An Attempted System of the Elements Based on Their Atomic Weights and Chemical Analogies (flyer). 

The first attempt is not to be confused with the Attempted System. Whereas the Attempted System (Figs. 11.1 and 11.2) represents the end-product of the process of discovery, Mendeleev most probably wrote down the first attempt at the very beginning of his quest for a classification of the elements. 

The inclusion of this rather severe criticism might be viewed as an attempt by the editor of Chemical News to temper his initial enthusiasm for Mendeleev s system, which had led to the 17-part serialization. Why he would otherwise choose to follow the priority dispute with this note is difficult to rmderstand. 

In the context of writing his Principles of Chemistry textbook, Mendeleev formulated his first version of the periodic system of chemical elements in the first two months of 1869. He would spend the next two years elaborating upon this system, expanding the scope and utility of the system in a variety of ways classification of peroxides, the properties of rare earth metals, and, especially, the detailed prediction of properties of three yet-undiscovered chemical elements, which he named eka-aluminum, eka-boron, and eka-silicon. After the publication of these predictions in his most detailed article on the chemistry of the periodic system in 1871 [Mendelejew, 1871], Mendeleev attempted briefly to experimentally discover these elements himself, but quickly abandoned the project by the end of that calendar year. 

Mendeleev s system has often been considered important for teaching, and his attempts to write a textbook are often taken as the initial step in the chain of thoughts that led to the periodic system. I will therefore start by looking at how textbooks in chemistry in Sweden structured their material, before and after Mendeleev. Thereafter, I will shortly say something about the atheoretical attitude, before going into the system s effects on laboratory work. 

In this essay I examine how the periodic system or table was introduced in Denmark in the late nineteenth century, how it was used in chemical textbooks, and the way it was developed by a few of the country s scientists. Danish chemists had in the period an international orientation, which helped them in getting acquainted with Mendeleev s system and appreciating its strength. The main reason they felt the system to be attractive was its predictive force, especially its prediction of new elements and ability to accommodate new chemical knowledge. I pay particular attention to the work of Hans Peter Jorgen Julius Thomsen (1826-1909), which is an important example of neo-Proutean attempts to understand the periodic system in terms of internally structured atoms. Moreover, I direct attention to Mendeleev s connection to Danish science by way of his membership in the Royal Danish Academy of Sciences and Letters. 

To understand how the electron has been applied to explanations of the periodic table we must start with the discovery of the periodic system itself. The Russian chemist Dimitri Mendeleev announced in 1869 that the properties of elements arranged in order of increasing atomic weight appeared to repeat after certain definite intervals. Yet even as this discovery became increasingly well established, Mendeleev remained strongly opposed to any attempt to reduce or explain the periodicity in terms of atomic structure. He resisted the notion of any form of primary matter, which was actively discussed by his contemporaries, and opposed... 

Figure 2. Dimitri Mendeleev s discovery of the periodic system in 1869 was quickly followed by controversy over how it should be used, Mendeleev resisted reduction or explanation of the system in terms of atomic structure, and was specifically opposed to attempts to draw curves through points representing numerical data Lothar Meyer, who contributed to the discovery of the periodic system, was not so averse to reduction, however. One of his graphs, shown here in an 1870 publication, plotted atomic volume and was instrumental in the acceptance of the periodic system.

Arguably, however, Mendeleev s greatest achievement was not the periodic table so much as the recognition of the periodic system on which it was based. Of the nearly 1,000 variations that have been published since, all are attempts to represent the fundamental rule that after certain but varying intervals, the chemical elements show an approximate repetition in their properties. 

A similar activity is found in Mendeleevs first attempt at a periodic system as presented in a hand-written table. If one examines the calculations that he is carrying out one finds again an attempt to compute differences between the atomic weights of elements in the columns of his table. For example Mendeleev writes the number 27 in smaller writing below the symbols for potassium (Zn - K = 65 - 39 = 27) and again below rubidium (Cd-Rb = 112-85 = 27). 

New scientific methods (e.g. electrolysis) allowed the veteran elements to be joined stepwise by more and more unknown and unexpected substances that fulfilled the criteria for an element. In 1869, after many attempts to bring order into the growing chaos, Dimitri Mendeleev revealed a daring concept with his Periodic Table and its predictions. Each of the then known elements was assigned a place. The gaps represented elements that were not yet known. The discoveries of such elements proved that there was an order and system to the elements. This order explained much that was previously puzzling, for instance, the different atomic radii observed that same year by Julius Lothar Meyer, which seemed to follow a periodic trend. 

What is the best didactic and graphic way of representing the periodic system The representation dating back to Dmitri Mendeleev has successfully stood the test of time. Nevertheless there have always been and still are attempts to represent the relationships in different formats. This task always poses one particular challenge The occupation of the orbitals by electrons should be clearly recognizable. In most cases, however, the overview is lost. Some proposals are represented here. Some are quite new, which shows that the search has not yet ended. 

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