Dmitri Mendeleev

Dmitri Ivanovich Mendeleev (1834–1907) was a Russian chemist, who is often considered the principal discoverer of the Periodic Table of the Elements—perhaps the single most-important, unifying idea in the field of chemistry, as well as one of the most recognizable icons in all of science.

Mendeleev (in older literature, the name is usually transliterated as “Mendeleyev”) was born in Verkhnie Aremzyani, a village near Tobolsk, in Siberia. His father was a schoolmaster and sometime secondary school philosophy professor. His grandfather was a Russian Orthodox priest. He was the youngest of 14 brothers and sisters who survived early infancy.

The young Mendeleev attended gymnasium at Tobolsk, then traveled to Saint Petersburg, where he matriculated at the Imperial University—his father’s alma mater—in 1850, at the age of 16. After a stint teaching in a Gymnasium in Crimea–where he had gone to recuperate from a bout of tuberculosis—he worked as a technical assistant to Robert Bunsen (1811–1899) at the Heidelberg Universityin Germany between 1859 and 1861. While in Germany, he studied capillary action and spectroscopy.

In 1861, back home in Russia, Mendeleev published a prize-winning textbook on organic chemistry. The following year, he got married and took a job at the Nikolaev Engineering Institute in Saint Petersburg. After relatively brief stints of teaching at the Saint Petersburg State Institute of Technology and Saint Petersburg State University, in 1865 he published a doctoral dissertation titled “On Compounds of Alcohol with Water,” earning him the Doctor of Science degree. In 1867 he was appointed to a tenured chair in general chemistry at the Imperial University of Saint Petersburg, where, under his leadership, the chemistry department became a research center that came to enjoy a considerable international reputation.

Mendeleev published two major papers on the periodic law, or system, and its representation in tabular form, in 1869 and 1871 (see below). He continued refining and attempting to extend his version of the periodic system throughout the rest of his life. In 1880 he entered into a priority dispute with Lothar Meyer (1830–1895). Although Mendeleev’s version of the periodic table carried the day, becoming generally accepted by around 1885, he spent much of his effort in his later years in a vain attempt to account for several stubborn anomalies which still remained and whose ultimate solution would have to await the advent of the quantum theory during the early decades of the twentieth century.

How did Dmitri Mendeleev contribute to the periodic table?

The history of the development of the periodic table of the elements is complex and, in part, contentious. The following is a brief summary of this complicated story, based as much as possible on consensus among historians of science.

The idea that specific chemical affinities exist among the various elements is lost in the mists of empirical practices such as alchemy and metallurgy. In the seventeenth century, Robert Boyle (1627–1691) and others began to put this traditional body of knowledge onto a firmer experimental foundation, while during the eighteenth-century, in what came to be known as the “Chemical Revolution,” experimentalists and theoreticians such as Joseph Priestley (1733–1804), Antoine Lavoisier (1743–1794), Humphrey Davy (1778–1829), and others began to vastly expand the boundaries of knowledge of chemical affinities among the chemical elements and their compounds.

Around the turn of the nineteenth century, John Dalton (1766–184) proposed the first modern, scientifically based theory that all matter is composed of tiny, indivisible, fundamental particles. Dalton called his hypothetical particles “atoms” after the ancient Greek school of Democritus (c. 460–c. 370 BC). Around the same time, Dalton, Jöns Jacob Berzelius (1779–1848), and others set about methodically investigating the atomic weights of the known elements. It was hoped that better values for these magnitudes would help to advance understanding of chemical affinities. Working from these improved estimates, in 1815 William Prout (1785–1850) advanced the hypothesis that now bears his name: the atomic weights of all elements are approximately integer multiples of the weight of hydrogen.

These three advances—the improved determination of atomic weights; Dalton’s atomic hypothesis; and Prout’s hypothesis that all the elements are essentially composed of hydrogen atoms—set the stage for the race to establish a new system of numerical relationships among the known elements. This is the essential background against which the development of the periodic table of the elements must be seen. Initial efforts to make sense of the overall system of chemical affinities may be divided into several stages. In the first stage, Johann Wolfgang Döbereiner (1780–1849), Leopold Gmelin (1788–1853), and others attempted to arrange the known elements into various series based on increasing atomic weights. Notably, they drew attention to what they termed “triads”—groups of three consecutive elements, the middle term of which has an atomic weight that is approximately the arithmetic mean of the weights of the two adjacent elements.

In a second stage, a number of chemists tried to create a synthetic system encompassing all of the known elements. Among the most important of these, one may name Max Joseph von Pettenkofer (1818–1901), who was the first to identify larger repeating series, or “periodicities” (of 5, 8, and 16 elements) and to suggest using the known relationships in order to discover new elements. Another important contributor at this stage was Alexandre-Émile Béguyer de Chancourtois (1820–1886), who was the first to create a two-dimensional table of rows and columns representing quantitative numerical periodicities and shared qualitative chemical properties, respectively. Still another important investigator active at the same time is John Newlands (1837–1898), who created a table based on a periodicity of 8, which he called the “law of octaves.” This representation of the elements was one of the most accurate prior to the tables to be discussed in the next section.

Finally, the first clear breakthrough to a roughly modern understanding of the periodic law saw the light of day in 1864 in a textbook written by Lothar Meyer (already mentioned above). In this work, Meyer included three alternative versions of a tentative periodic table, which together were superior in several different ways to anything published before. First, he made use of greatly improved values of atomic weights, which had been reported by Stanislao Cannizzaro (1826–1910) at a scientific conference held in Berlin in 1860. In addition, Meyer made novel use of certain physical properties of the various elements, such as volume and density, that he had calculated himself. Finally, he offered his three proposals as possible forms of a single unified system of all the elements, unambiguously based on the principle of increasing atomic weights. Others had published different aspects of this work before, but up to that time no one had synthesized them in the way that Meyer did.

In a follow-up version of his system published in 1870, Meyer displayed the qualitative groupings along a vertical axis (though this, too, had been done before by de Chancourtois), in a single unified table of 52 elements with a horizontal periodicity of 15. With this final step, Meyer arrived at a table very similar to the one first devised by Mendeleev in February of 1869 and published (albeit in Russian) later the same year and in a much-improved version in German in 1871 (see below). Indeed, of the two, Meyer’s was superior in that it contained fewer errors. However, Meyer’s presentation of his ideas in his 1870 paper was highly diffident, in the accepted German academic fashion, which at the time was hostile to purely theoretical work. Moreover, he did little to follow up on his groundbreaking 1870 paper. Finally, we arrive at the contribution of Mendeleev himself. In a nutshell, he arrived at a system very similar to Meyer’s some five years after Meyer had published his preliminary versions. The major difference between the reputations of the two men seems to derive from the fact that for Meyer the system set out in his 1870 paper was the capstone of his work on the periodic table, while for Mendeleev, the breakthroughs reported in his 1869 and 1871 papers were just the beginning. Let us, then, look at Mendeleev’s accomplishment in more detail.

What did Dmitri Mendeleev do?

Mendeleev had long been intrigued by the relationship between the physical and chemical properties of minerals. His first publication, in 1854 when he was a 20-year-old undergraduate, was the chemical analysis of a sample of orthite (Allanite)—a silicate containing rare-earth elements—from Finland. His senior thesis, published in 1855, was a literature review of what was then known about the phenomenon of crystal isomorphisms. However, Mendeleev himself tells us that it was his appointment to the chair of general chemistry at the Imperial University of Saint Petersburg in 1867 that led him directly to his famous discovery. Among his new duties was that of teaching the main undergraduate class in inorganic chemistry, and upon reviewing the Russian introductory textbooks available to him and being dissatisfied with them all, he decided to write his own book. (Remember that he had already published a successful organic chemistry textbook back in 1861.)

Mendeleev began to publish his new textbook, Osnovy khimii [Principles of Chemistry], in 1868, with the intention of publishing supplementary volumes (which appeared in 1870 and 1871). It was during his continuing effort to impose some theoretical order on the mass of empirical knowledge he had amassed for the second volume that he finally hit on the periodic law.

We even know the exact date when the basic idea for Mendeleev’s system occurred to him: February 17, 1869. He later writes that he was scheduled to give a lecture at a dairy farm that day, but became so absorbed in the vision of the periodic table unfolding before his mind’s eye that he forgot all about the lecture. Trying one arrangement after another on scraps of paper, by the end of the day he had drawn up his first version of the periodic table. Giving it the title “Attempt at a System of the Elements Based on Their Atomic Weights and Chemical Similarity” and attaching several brief comments to it, he had 200 copies privately printed and circulated them among colleagues both in Russia and in Germany. One of Mendeleev’s colleagues in Saint Petersburg, Viktor von Richter (1841–1891), a Baltic German fluent in both languages who had valuable personal connections among scientists in Germany, helped him out with this.

The following month, Mendeleev delivered a fuller version of the paper, now titled “The Relation of the Properties of the Elements to Their Weights,” before the Russian Chemical Society, who soon published it in their journal. An abstract of the latter publication also appeared in German before the year 1869 was out.

Mendeleev was convinced that with the periodic law he had hit upon a veritable law of nature. On the other hand, he was quite aware that there were gaps in his system and its tabular representation as developed so far. Therefore, he set to work to re-examine the entire empirical foundation of his work—namely, Cannizzaro’s estimates for the atomic weights, which Mendeleev too had learned of at the 1860 Berlin conference. Indeed, Mendeleev was so sure that the basic principle of the periodic law—which he viewed as an exceptionless law of nature—was essentially correct that he even sent so far as to revise Cannizzaro’s and others’ empirical findings where necessary on the basis of his own theory. It is interesting that Mendeleev’s seeming hubris in prioritizing theory over observation in this way turned out to be well founded.

What did Mendeleev predict about the elements?

For two years, Mendeleev worked to perfect his system. While he could not produce a complete periodic table because several elements had not yet been discovered, he had no qualms about predicting the placement and even the detailed chemical properties of missing elements. Most notably, he predicted both the quantitative (atomic weight) and qualitative (chemical) properties of three important missing elements: the ones that came to be called germanium, gallium, and scandium.

Mendeleev published the fruit of these two years of labor in two classic papers. The first appeared in Russian in 1870 and was titled “The Natural System of the Elements and Its Application to the Demonstration of the Properties of Undiscovered Elements.” The second was published in German in 1871 and titled “Die periodische Gesetzmässigkeit der chemischen Elements” [The Periodic Law of the Chemical Elements]. This latter paper, which appeared in the internationally celebrated journal, Justus Liebig’s Annalen der Chemie, was highly detailed and numbered almost 100 pages in length. In it, Mendeleev provided elaborate evidence for his many pathbreaking claims. The form of periodic table published in this paper consisted of a grid of eight columns and 12 rows, integrating all of the then-known elements, as well as several unknown ones.

The 1871 paper was very widely read and commented upon. However, Mendeleev’s version of the periodic table did not gain general acceptance for some time. The three key predictions from the 1871 paper—the existence and properties of the elements we now call germanium, gallium, and scandium—were gradually discovered by others over the next decade and a half or so. After about 1885, the outstanding success of Mendeleev’s predictions was evident to everyone, causing his version of the periodic system to sweep away all competition.

Why is Mendeleev considered to be the father of the periodic table and not Julius Lothar Meyer?

The reason we have tarried so long over some of the details of the complex history of the discovery of the periodic table of the elements is precisely to illustrate why there is no simple answer to the question: Who is its real discoverer? The fact is that the periodic system gradually evolved over several decades. Evolution, not revolution, is the operative word here—as elsewhere in the history of science. Nevertheless, it is true that Lothar Meyer’s version of the periodic table was very similar to Mendeleev’s—indeed, it was superior in some ways—and that it reached its initial fruition in print (to say nothing of its preliminary glimmerings in Meyer’s mind) in 1864, some five years before Mendeleev’s first breakthrough. There is no doubt, then, that Meyer deserves considerable credit for the achievement of a major advance within the overall evolutionary history of the periodic table.

Why, then, does everyone know Mendeleev’s name and almost no one Meyer’s? In one sense, the answer clearly lies in the specific predictions made by Mendeleev, whose persuasive force carried the day for his system. However, that observation merely begs the question: What gave Mendeleev the confidence to stick his neck so much farther than Meyer dared to do?

In another sense, part of the answer may lie in the fact that Mendeleev benefited from the influence of several new members on the editorial board of Liebig’s Annalen, who were more open to the kind of daring, theoretical work represented by Mendeleev’s 1871 paper. Whereas Meyer had pulled his punches—“buried the lead,” one might almost say—in his paper of the year before, apparently out of fear of appearing improperly incautious to the staid German academic world of the day, Mendeleev was able to get away with playing the dashing young Byronic figure. In short, the world was changing in Mendeleev’s favor.

Perhaps so. But, then, Mendeleev had put in two grueling years to produce the empirical evidence to back up his daring theoretical claims. In the light of that salient fact, it seems intellectually ungenerous to dwell too much on the minutiae of social networking and publication.

What, then, gave Mendeleev the courage to pursue his idea so single-mindedly? Was it merely a difference of cultural climate? Or perhaps one of individual temperament?

In yet another sense, at least part of the answer surely lies in the fact that Meyer and Mendeleev saw the enterprises they were engaged upon quite differently. Meyer still stood in an earlier tradition that was fundamentally empiricist in orientation. Science was deemed to be about producing theories to “save the phenomena.” One did not take the theories themselves too seriously. They were seen primarily as instruments that helped scientists to make sense of the world.

Mendeleev, on the other hand, subscribed to a quite different philosophical tradition. He believed that all of nature is governed by exceptionless laws analogous to the law of gravity and that it had been given to him to discover the universal law governing the elements, their properties, and their modes of combination. On this view, it was Mendeleev’s philosophical realism that gave him the confidence to believe in the truth of his own system, to use that system to correct recalcitrant empirical observations (and not the other way around), and to boldly announce the predictions that ultimately convinced his fellow scientists—whatever their philosophical persuasion might be—of that truth.