Yet, the periodic table is not as objective as that basic description may sound. And who deserves credit for its creation is also not straightforward. I am a theoretical chemist ; I apply chemical principles and mathematics to answer questions and solve problems in various areas of chemistry. Those interests coupled with my chemistry background have led me over the years to intersections of the political and the scientific in the emergence of the modern periodic table.
There are, for instance, nationalistic tilts to the periodic table. Two elements francium and gallium are named for France and one each for Japan nihonium , Germany germanium , and Poland polonium.
Scandinavia got scandium; the elements berkelium, darmstadtium, and moscovium give three cities each a spot on the table. One Swedish village—Ytterby—has claimed four elements: erbium, terbium, ytterbium and yttrium. A number of other places and people have also snagged their little rectangles on the table too, and that, in some cases, only after serious disputes. Among the elements named after people is element number , mendelevium Md , which honors Mendeleev.
Resisting other self-serving instincts, a group of Berkeley scientists who discovered the radioactive Md in decided to honor the Russian scientist Mendeleev for his contributions to formulating the periodic table. With the Cold War underway, however, they had to convince the Eisenhower administration to allow them to give up a spot on the table to a deceased Russian.
Mendeleev published in a paper that organized then-known elements in an authoritative, logical, and systematic way, and he boldly predicted new ones. That paper was followed by others in the early s that improved on the first and demonstrated the value of a deep appreciation for the periodicity in chemistry. He, his papers, and his table garnered a lot of attention and accelerated progress in our collective understanding of the elements and their relationships to each other. At the end of a chemical congress in Karlsruhe, Germany, in September , for instance, a decisive paper by Cannizzaro on the weights of the atoms of the elements was distributed to the attendees.
Lothar Meyer , reported that it felt to him as if the scales fell from his eyes as he gained a new understanding of the elements. Newlands had also predicted the existence of other elements. Predictably, a slowly festering dispute over priority eventually erupted between them. Does Mendeleev deserves credit for producing a superb table for his time, for advancing an understanding of how the properties of atoms are rhythmically linked, for underlining the power of that understanding and for brave predictions that pushed chemistry forward?
Although we have retained the format of rows and columns, which reflects a natural order, the rows of today's tables show elements in the order of Mendeleev's columns. In other words the elements of what we now call a ' period' were listed vertically by Mendeleev.
Chemical 'groups' are now shown vertically in contrast to their horizontal format in Mendeleev's table. It is also worthy to note that Mendeleev's arrangement was related to the atomic ratios in which elements formed oxides, binary compounds with oxygen whereas today's periodic tables are arranged by increasing atomic numbers, that is, the number of protons a particular element contains. Although we can imply the formulas for oxides from today's periodic table, it is not explicitly stated as it was in Mendeleev's table.
The oxides ratio column was not shown in earlier Mendeleev versions. Mendeleev rewrote each edition of Principles of Chemistry , including all new scientific data-particularly confirmations of the periodic law-and reanalyzing difficulties that had arisen to hinder its confirmation inert gases, radioactivity, radioactive and rare-earth elements ".
Connect with us Contact us today. He calculated differences between pairs of elements belonging to each of these groups in the hope of finding some significant pattern. But he appears to have been disappointed because the differences between the corresponding elements he considered show no regular pattern. Nevertheless, Mendeleevdid not quite dismiss the idea of following the alkali metals by the group containing zinc and cadmium because this is precisely what he did in a second classic document in which he now included many more known groups of elements in the first of two tables of elements which appear on the same sheet of paper figures 2 and 3.
Whereas the upper table shows the zinc and cadmium group directly above the alkali metals, the lower of the two tables shows a rearrangement in which Mendeleev has decided to place the typical alkaline earth metals next to the alkali metals by moving the alkali metals up the table as an entire block.
The net result is that the halogens are followed by the alkali metals, which in turn are followed by the alkali earths. The consequence of this move is that the sequence of atomic weights now appears more orderly than it did in the earlier upper table on the same page. As a result of this simple change Mendeleev appears to have realized that a successful periodic table requires not only a correct grouping of elements in adjacent rows but also a set of smoothly increasing sequences of atomic weights.
Here is where he first sees that the periodic table is a display of chemical periodicity that is itself a function of the variation of atomic weight. For example, note the atomic weight sequence of Cl Alternatively, consider the placement of K 39 which seems out of place next to Cu 63 in the upper table as compared to its proximity with elements of similar atomic weights in the lower table.
The essential point seems to be that Mendeleev began by considered groups of chemically similar elements and that the notion of ordering according to atomic weight came to him later. And this document appears to be precisely where he arrived at this conclusion. Interestingly, the current director of the Mendeleev Museum, Professor Igor Dimitriev, disagrees with this account of the development. He believes that the document sketched on the back of the invitation from the cheese co-operative figure 1 , did not precede the two-tables on a single sheet document Figures 2 and 3.
There is little doubt in my own mind that the notion of groups of chemically similar elements was well rather established and that it would have been natural for Mendeleev, who followed the above named authors, to begin with this notion. On the other hand the idea of using the sequence of increasing atomic weights to order the elements was nowhere near as well-established and it had only been a few years since the Karlsruhe conference of at which atomic weights had been unified and rationalized to produce a more or less definitive list of values that every chemist agreed with.
I think the answer to this question is both yes and no. I suspect that his custodianship of the St. Petersburg museum and archives may have led Dimitriev to concentrate upon the work of Mendeleev above that of all others. Finally, could it be that Dimitriev, who like Mendeleev is a Russian, may have allowed national pride to influenced his judgment of the issue and to perhaps downplay the contributions of foreign scientists.
What did he do after he had produced the lower table in figure 2? The aim of this well-known game is to arrange the cards in two senses. First of all the cards must be in separate suits and secondly they must be in order of decreasing values starting with king, queen, knave, ten and so on reading from left to right. The plot thickens further when one learns that Mendeleev kept almost everything as soon as he realized that he would become famous.
No such cards have ever been found, although it could just be that Mendeleev had not quite realized his impending fame at this stage. The game of chemical solitaire provides such a good analogy that it is more important to focus on that than trying to determine whether Mendeleev actually used this approach or not.
In the case of the periodic table, there is a beautiful analogy given that the elements are arranged in groups as opposed to suits, and along another direction they are arranged in order of increasing values of atomic weights, as opposed to decreasing values on cards. Although Mendeleev was a true genius for discovering the periodic table, there is a real sense in which the periodic system is inevitable and provided by Nature itself.
It was just a matter of uncovering this profound truth.
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