Mendeleev on the Periodic Law: Selected Writings, 1869 - 1905

By Dmitri Ivanovich Mendeleev

By the dawn of the nineteenth century, "elements" had been defined as basic building blocks of nature resistant to decomposition by chemical means. In 1869, the Russian chemist Dmitri Ivanovich Mendeleev organized the discord of the elements into the periodic table, assigning each element to a row, with each row corresponding to an elemental category. The underlying order of matter, hitherto only dimly perceived, was suddenly clearly revealed.
This is the first English-language collection of Mendeleev's most important writings on the periodic law. Thirteen papers and essays, divided into three groups, reflect the period corresponding to the initial establishment of the periodic law (three papers: 1869-71), a period of priority disputes and experimental confirmations (five papers: 1871-86), and a final period of general acceptance for the law and increasing international recognition for Mendeleev (five papers: 1887-1905). A single, easily accessible source for Mendeleev's principle papers, this volume offers a history of the development of the periodic law, written by the law's own founder.

• Language: English
• Publisher: Dover Publications
• Release date: Apr 25, 2013
• ISBN: 9780486150420

Book preview

13

General Introduction

BOTH the story of the discovery of the periodic law and the key role played in that discovery by the 19th-century Russian chemist, Dmitri Ivanovich Mendeleev (1834-1907), are well-known and need not be repeated here (¹,²). However, given that the periodic law currently enjoys a status in chemistry not unlike that of the theory of evolution in biology, it is rather curious that so far no attempt has been made to provide an English-language collection of Mendeleev’s most important writings on this subject. Neither the series of scientific classics published by Harper at the turn of the 20th century (³), the famous Alembic Club translation series (⁴), nor the scientific reprint series initiated by Dover Books in the 1960s (⁵) included papers by Mendeleev on the periodic law. In 1970 the British historian, David Knight, did include several reprints in a two-volume collection of classic 19th-century papers on chemistry (⁶). However, these appeared without bibliographic commentary and as photographic reproductions of the originals in which several footnotes and, in at least one case, an entire column of print were accidentally deleted. The few other collections of scientific classics that have included Mendeleev’s work have mostly reprinted only short extracts from his papers (⁷, ⁸, ⁹, ¹⁰, ¹¹, ¹²).

As might be expected, the situation in Mendeleev’s native country is far different. Since his death, several collections of his writings on the periodic law have appeared in Russian (¹³, ¹⁴, ¹⁵, ¹⁶, ¹⁷) and an English translation of these would not only be of great interest to American historians of chemistry but utterly indispensable to anyone wishing to write a definitive biography of Mendeleev. Regrettably such a project is well beyond the abilities of this editor and what is attempted in this small volume is far more limited in scope. Examination of the contents of these Russian collections reveals that many of Mendeleev’s papers on the periodic law were never translated into German, French, or English. However, as important as these untranslated documents are, from a biographical point of view, for tracing the development of Mendeleev’s personal thought on this subject, they essentially played no role in making the periodic law known to American, British and western European chemists.

Despite the great strides made since Peter the Great, the westernization of Russia still remained problematic in the minds of many 19th-century European scientists, few of whom, as the German chemist Lothar Meyer bitterly complained, when accused by Mendeleev of needlessly repeating his work, could be expected to be fluent in Russian as well as German, English, French, and Italian (¹⁸). And this isolation cut both ways. As indicated in the quotation following the title page of this collection, the famous British chemist, Sir William Ramsay, reported having a conversation with Mendeleev in 1884 in which Mendeleev confessed that he not only did not speak English, but had not learned Russian until he was 17 years old. The conversation in question was conducted in German, and Ramsay reported that Mendeleev’s command of that language was also less than perfect (¹⁹). Consequently, in this volume we have collected together English translations of only those writings of Mendeleev on the periodic law that were actually translated from Russian during his lifetime. Though it sounds both parochial and politically incorrect, the fact remains that only these translated writings played an important role in gaining general acceptance for the periodic law as a fundamental chemical principle outside of Russia and the various Slavic countries. In other words, only these papers, to use Alfred North Whitehead’s felicitous phrase, were efficient in the stream of science (²⁰).

Based on these constraints, I have selected thirteen papers and/or essays by Mendeleev for inclusion in this collection, all of which were translated into German, French or English between 1869 and 1905. Though several of Mendeleev’s other publications on the periodic law were briefly summarized in German in the Berichte der deutschen chemischen Gesellschaft during this same period, these summaries were presumably provided by the Berichte’s Russian correspondent rather than by Mendeleev himself and, for this reason, have not been included. The papers are presented in roughly chronological order and have been divided into three groups, reflecting the period corresponding to the initial establishment of the periodic law (three papers: 1869-1871), a period of priority disputes and experimental confirmations (five papers: 1871-1886), and a final period of general acceptance for the law and increasing international recognition for Mendeleev (five papers: 1887-1905). In keeping with these choices, I have used both 19th-century and modern English translations from the German and French, rather than fresh translations from the Russian originals. Though there is some reason to suspect that these older translations were not always of the best quality, they are, nonetheless, the versions read by 19th-century chemists outside of Russia and thus reflect their understanding of the periodic law even if they do not always accurately reflect Mendeleev’s original intentions.

Though bibliographic details of the individual translations are given in the introductions to the various sections, it may not be amiss to say something here about some of the more general editorial decisions:

1. In the case where Mendeleev’s papers were translated into German or French during the 19th-century, but not into English, the English translations appearing in this collection are new and have been made from the German or French primary translations especially for this book. In those cases where 19th-century English translations do exist, they are invariably British in origin and abound, by modern standards, in complex and awkward sentence structures, run-on sentences, and questionable word and punctuation choices. Since many of them are translations of German or French translations of Russian originals, it is not always obvious how much of this awkwardness is due to the various translators rather than to Mendeleev himself. Consequently, after considerable deliberation, I have decided, in the interests of greater clarity, not to literally reproduce these secondary and tertiary British translations, but rather to use them as a basis for a set of revised translations based directly on a comparison with the original primary German and French translations. This decision reflects my own preference for liberal translations (even to the point of paraphrase) which maximize clarity, rather than literal translations, which tend to become entangled in complex and unusual sentence structures and word choices. Though, in doing this, I have tried to retain as much of the British originals as I felt was consistent with these goals, this decision has naturally resulted in many minor changes in the punctuation, in the word order and sentence structure, in the use of more appropriate synonyms, in the Americanization of the spelling, etc. Of course, should a reader become convinced that some epic issue in the history of chemistry depends on the original placement of a comma or a subordinate clause, they can always consult the originals instead.

2. In keeping with the above decision, I have also taken the liberty of breaking some of Mendeleev’s original paragraphs into smaller units. Some of these go on for two or three pages, and this decision was made not only for reasons of greater clarity, but because my computer absolutely refused to process paragraphs of such length.

3. The bibliographic citations within Mendeleev’s own papers are erratic. Sometimes he gives author, title, journal, volume, date, and page, whereas other times he gives just the journal and date. Sometimes he embeds the citation in parentheses within the body of the text, whereas other times he footnotes it at the bottom of the page. I have not attempted to upgrade Mendeleev’s original citations and have left them exactly as he gave them, however abbreviated. Nor have I removed those citations embedded within the body of the text. However, all footnotes appearing at the bottom of the pages of the original publications have been renumbered and placed at the end of the each paper, not only for purposes of greater uniformity, but because it creates fewer technical problems in laying out the text itself.

4. The spelling of both Mendeleev’s last and middle names has varied over the years due to shifting fads in transliteration. I have used the modern American conventions of Ivanovich and Mendeleev whenever referring to him in the various introductions or citing him as an author. However, when his name appears in the title of a cited book or paper, I have retained whatever spelling was used by the author in question.

5. Though the papers included in this collection often refer to chemical concepts and terms unfamiliar to the modern chemist and hence present a great scope for historical annotations, I have concluded – again after considerable deliberation – that these, if done properly, would unduly increase the size of the volume and have instead allowed the documents speak for themselves.

References and Notes

1

The most comprehensive scholarly history of the periodic law is still J. W. van Spronsen, The Periodic System of Chemical Elements, Elsevier: Amsterdam, 1969. For a recent popular account see, P. Strathem, Mendeleyev’s Dream, Hamilton: London, 2000.

2

There is at present no modern, comprehensive biography of Mendeleev available in English. Older German and English-language sources include: (a) P. Walden, Dmitri Iwanowitsch Mendelejeff, Berichte, 1908, 41, 4719-4800. (b) W. A. Tilden, Mendel6eff Memorial Lecture, J. Chem. Soc.,1909, 95, 2077-2105. (c) E. Thorpe, Essays in Historical Chemistry, Macmillan: London,1911, pp. 483-499. (d) B. Harrow, Eminent Chemists of Our Time, 2nd ed., Van Nostrand, New York, NY, 1927, pp. 19-40, 273-285. (e) D. Q. Posin, Mendeleyev: The Story of a Great Scientist, McGraw-Hill: New York, NY, 1948. (f) O. N. Pisarzhevsky, Dmitry Ivanovich Mendeleyev: His Life and Work, Foreign Languages Publishing House: Moscow, 1954. (g) H. Leicester, Dmitri Ivanovich Mendeleev in E. Farber, Ed., Great Chemists, Interscience; New York, NY, 1961, pp. 719-731. (h) K. Danzer, D. I Mendelejew und Lothar Meyer: Die Schöpfer des periodischen Systems der chemischen Elemente, 2nd ed., Teubner: Leipzig, 1974. (i) B. M. Kedrov, Dmitri Ivanovich Mendeleev, in C. C. Gillespie, Ed., Dictionary of Scientific Biography; Vol. 9, Scribners & Sons: New York, NY, 1974, pp. 286-295. The memoir by Walden (1a) contains a complete bibliography of Mendeleev’s published papers and books. An incomplete bibliography in English translation is also given in Posin (1e). In addition, there are at least a half dozen Russian-language biographies of Mendeleev, a partial list of which is given in reference 1h.

3

J. S Ames, Ed., Harper’s Scientific Memoirs, Harper & Brothers, New York, NY. Titles in chemistry included: (a) H. C. Jones, Ed., The Modern Theory of Solutions, 1899. (b) C. Barus, Ed., The Laws of Gases, 1899. (c) G. M. Richardson, Ed., The Foundations of Stereochemistry, 1901.

4

Alembic Club Reprints, 22 vols., Livingston: Edinburgh, 1898-1958. Each booklet contained selected reprints and/or translations of classic papers, either complete or in the form of short abstracts, on specific areas of chemistry.

5

G. Holton, Ed., Classics of Science, Dover: New York, NY. Titles in chemistry included: (a) O. T. Benfey, Ed., Classics in the Theory of Chemical Combination, 1963. (b) G. Kauffman, Ed. Classics in Coordination Chemistry, Parts 1-3, 1968, 1976, 1978. (c) A. Romer, Ed., Radiochemistry and the Discovery of Isotopes, 1970.

6

D. M. Knight, Ed., Classical Scientific Papers: Chemistry, Second Series, American Elsevier: New York, NY, 1970. Reprints of papers 1, 3, 9.

7

H. M. Leicester, H. S. Klickstein, Eds., A Source Book in Chemistry, 1400-1900, Harvard University Press: Cambridge, MA, 1952, pp. 438-444. Extracts from papers 2 and 3.

8

G. Schwartz, P. W. Bishop, Eds., Moments of Discovery, Vol. 2. Basic Books: New York, NY, 1958. Extracts from paper 2.

9

W. C. Dampier, M. Dampier, Eds., Readings in the Literature of Science, Harper: New York, NY, 1959, pp. 112-117. Extracts from paper 9.

10

D. L. Hurd, J. J. Kipling, Eds., The Origins and Growth of Physical Science, Vol. 2, Pelican Books: Baltimore, MD, 1964, pp. 81-100. Extracts from paper 2.

11

M. P. Crosland, Ed., The Science of Matter, Penguin Books: Harmondsworth, 1971, pp. 285-288. Extracts from paper 9.

12

A. S. Weber, Nineteenth Century Science: A Selection of Original Texts, Broadview Press: Orchard Park, NY, 2000, pp. 398-416. Reprint of paper 9.

13

Mendeleev’s writings on the periodic law appear in volume 2 of his collected works. See, D. I. Mendeleyev, Sochineniia, 25 vols., Isd. AN SSSR: Leningrad, 1934-1956.

14

D. I. Mendeleyev, Novye materialy po istroii otkrytiia periodicheskogo zakona, Akademiia nauk SSSR: Moscow, 1950.

15

D. I. Mendeleyev, Nauchnyi arkhiv: Periodicheskii zakon, Akademii nauk SSSR: Moscow, 1953.

16

D. I. Mendeleyev, Periodicheskii zakon, Akademii nauk SSSR: Moscow, 1958.

17

D. I. Mendeleyev, Periodicheskii zakon: Dopolnitelnye materialy, Akademii nauk SSSR: Moscow, 1960.

18

L. Meyer, Zur Geschichte der periodischen Atomistik, Berichte, 1880, 13, 2043.

19

W. Ramsay, Letter of 4 May 1884 to A. Blaikie. Quoted in W. Tilden, Sir William Ramsay: Memorials of his Life and Work, Macmillan: London, 1912, p. 89.

20

A. N. Whitehead, Science and the Modern World, Macmillan, New York, NY, 1925, p. 145.

Introduction to Papers 1-3:

Origins of the Periodic Law, 1869-1871

IN 1868 Mendeleev began writing his famous textbook, Principles of Chemistry ¹. As he later related, it was while exploring various alternative organizational schemes for this book that he hit upon the periodic law (², ³). While waiting for the book to appear in print (the first edition was published in installments between 1868 and 1871), Mendeleev produced a single-page flier summarizing his new organizational scheme entitled An Attempted System of the Elements Based on their Atomic Weights and Chemical Analogies, which he circulated among Russian chemists in early 1869 (⁴). In March of that year he presented a more detailed paper to the newly founded Russian Chemical Society (later known as the Russian Physico-Chemical Society) entitled On the Correlation Between the Properties of the Elements and their Atomic Weights (the paper was actually read by the Russian chemist, Nikolai Menshutkin, as Mendeleev was ill at the time). This, in turn, was published in the first volume of the society’s new journal and appears in English translation as paper 2 of this collection (⁵).

Why this publication does not appear as paper 1 is because it was not translated from Russian until 1895 and consequently played little or no role in initially acquainting American, British and western European chemists with the periodic law. This role was played instead by two short German abstracts of the paper, one of which appeared in the Journal für praktische Chemie (⁶) and the other in the Zeitschrift für Chemie (⁷). Neither of these abstracts served Mendeleev well. The first reproduced only Mendeleev’s table, without any commentary or explanation, whereas the second failed to mention the word periodic, stating instead that the elements displayed a step-like (stufenweise), rather than a periodic, alteration in their properties when arranged in order of increasing atomic weight. In addition, the second abstract also muddled a typo in the original paper in which Mendeleev intended to put forward the claim that the periodic law predicted an analogy between uranium, on the one hand, and both boron and aluminum, on the other, but instead stated the tautology that aluminum should be analogous to aluminum. The abstract replaced this with the equally obvious tautology that boron should be analogous to boron. To the best of our knowledge, only the longer abstract in the Zeitschrift für Chemie had a significant impact, as it was the reading of this abstract that stimulated the German chemist, Lothar Meyer, to publish his own thoughts on the periodic law in late 1870 and which ultimately gave rise to a vigorous priority debate (⁸, ⁹). It is the English translation of this abstract which is reproduced in this collection as paper 1.

In the summer of 1869 Mendeleev presented a paper to the Second Congress of Russian Physicians and Naturalists on the periodicity of atomic (i.e., molar) volumes and that autumn also made some supplementary comments to the Russian Chemical Society relative to his earlier paper on the periodic law (¹⁰, ¹¹). In 1870 he presented two additional papers to the Society dealing with the periodicity of oxide formulas (¹²) and the prediction of unknown elements (¹³). Though no abstracts of the first and third papers appeared in western journals, his supplementary comments and his fourth paper were both summarized in the Berichte der deutschen chemischen Gesellschaft by the journal’s Russian correspondent (¹⁴, ¹⁵). The latter of these summaries, in particular, showed that Mendeleev had made significant refinements in his original periodic table of 1869 (including the use of what later became known as the standard short table, with horizontal rather than vertical periods, and Roman-numeral group labels based on oxide type) and in his ability to predict the properties of as yet undiscovered elements. Finally, in 1871 Mendeleev summarized all of these previous publications in the form of a major review of the periodic law published in German in Liebig’s prestigious journal, Annalen der Chemie und Pharmacie (¹⁶). It is really this review, more than the papers and abstracts of 1869 and 1870, which defined the periodic law and table for the rest of the 19th century and which served as the primary reference for western chemists. It is reproduced in English translation as paper 3 of this collection.

The translation of paper 1 used in this collection is based in part on that given by Tilden in 1909 (¹⁷). As already mentioned, paper 2 was not translated from the Russian until 1895 – 26 years after its original publication – when Lothar Meyer’s student, Karl Seubert, commissioned a German translation by Fehrmann for inclusion in his volume of reprints on the periodic law published as part of Wilhelm Ostwald’s series, Klassiker der exakten Wissenschaften (¹⁸). However, Seubert reported that the resulting translation was not very satisfactory and contained many awkward phrases. Consequently he rewrote much of the original translation, though he claimed to have done so in a manner faithful to the original (¹⁹). About 90% of this German rewrite was translated into English in 1947 and made available in mimeographed form for use in a course at the University of Chicago (²⁰). This was reprinted by Schwartz and Bishop in 1958 (²¹) and again by Hurd and Kipling in 1964 (²²). The complete version given here is based on a revision of this translation with fresh translations of the missing sections added.

Paper 3 was originally written in Russian by Mendeleev and translated into German by Felix Wreden for publication in the Annalen der Chemie und Pharmacie in 1871 (16). The discovery of gallium by Lecoq de Boisbaudran in 1875 sparked a great interest in the periodic law among French chemists, and in 1879 the French journal, Le moniteur scientifique, published a French translation by Charles Baye of the 1871 review (²³). This, in turn, was translated into English and published in serialized form by William Crookes in The Chemical News in late 1879 and early 1880 (²⁴). Though Harrow called attention to this English translation in 1927 and Knight published a defective reprint of it in 1970, neither editor seems to have realized that it was a translation, however indirect, of the famous review of 1871, as Crookes had failed to indicate this fact in his serialization (²⁵, ²⁶). The original British translation shows signs of having been made in great haste and, even by Victorian standards, abounds in awkward phrases, word choices, and sentence structures, as well as containing incorrect formulas and occasional mistranslations. Consequently, the version given here, though based on the Crookes translation, has been extensively revised after comparison with the German original.

References and Notes

1

D. I. Mendeleev, Osnovyi khimii, Vols. 1 and 2, Obshchestvennaia pol‘za: St. Petersburg, 1868 – 1871.

2

Paper 2, this collection.

3

Discussion of the relation between Mendeleev’s textbook and his discovery of the periodic law may be found in L. Graham, Textbook Writing and Scientific Creativity: The Case of Mendeleev, National Forum, 1982 (Winter), 22 – 23; and N. M. Brooks, "Dmitri Mendeleev’s Principles of Chemistry and the Periodic Law," in A. Lundgren, B. Bensaude-Vincent, Eds., Communicating Chemistry: Textbooks and Their Audiences, 1789 – 1939, Science History Publications: Canton, MA, 2000, pp. 295 – 309.

4

See footnote 12 of selection 13 in this collection.

5

D. I. Mendeleev, On the Correlation Between the Properties of the Elements and their Atomic Weights, Zhur. Russ. Khim. Obshch, 1869, 1, 35, 60 – 77 (In Russian).

6

D. I. Mendeleev, Versuch eines Systems der Elemente nach ihren Atomgewichten und chemischen Funktionen, J. prakt. Chem., 1869, 106, 251.

7

D. I. Mendeleev, Über die Beziehungen der Eigenschaften zu den Atomgewichten der Elemente, Zeit. Chem., 1869, 5, 405 – 406.

8

L. Meyer, Die Natur der chemischen Elemente als Function ihrer Atomgewichte, Ann. Chem. Pharm., 1870, 7 (Suppl.), 354 – 364.

9

See papers 4 and 8 in this collection.

10

D. I. Mendeleev, Concerning the Atomic Volumes of Simple Bodies, Arb. II Kongr. Russ. Ärzt. Naturf., 1869 (In Russian).

11

D. I. Mendeleev, On the Correlation Between the Properties of the Elements and their Atomic Weights, Zhur. Russ. Khim. Obshch, 1869, 1, 229 – 230 (In Russian).

12

D. I. Mendeleev, On the Quantity of Oxygen in Metal Oxides and on the Valency of the Elements, Zhur. Russ. Khim. Obshch.,1870, 2, 14 – 21 (In Russian).

13

D. I. Mendeleev, Concerning the Natural System of the Elements and Its Application in Determining the Properties of Undiscovered Elements, Zhur. Russ. Khim. Obshch., 1871, 3, 7, 25 – 56 (In Russian).

14

D. I. Mendeleev, Die Beziehungen zwischen den Eigenschaften der Elemente und ihrer Atomgewichten, Berichte, 1869, 2, 553.

15

D. I. Mendeleev, Über das natürliche System der Elemente und seine Anwendung zum Ermitteln der Eigenschaften unentdeckter Elemente, Berichte, 1870, 3, 990 – 991.

16

D. I. Mendeleev, Die periodischen Gesetzmässigkeit der chemischen Elemente, Ann. Chem. Pharm., 1871, 8 (Suppl.), 133 – 229.

17

W. A. Tilden, Mendeléeff Memorial Lecture, J. Chem. Soc., 1909, 95, 2077 – 2105. Tilden corrected the error in conclusion 8 and mistakenly translated the word Maassstab or Massstab in conclusion 4 as unit of mass rather than as standard or measure.

18

K. Seubert, Ed., Das naturliche System der chemischen Elemente: Abhandlungen von Lothar Meyer 1864 – 1869 und D. Mendelejeff 1869 – 1871, Engelmann: Leipzig, 1895.

19

See the editorial comment at the bottom of page 20 of reference 18.

20

Anon., Selected Readings in Natural Science, University of Chicago: Chicago, IL, 1947.

21

G. Schwartz, P. W. Bishop, Eds., Moments of Discovery, Vol. 2. Basic Books: New York, NY, 1958, pp. 821 – 836.

22

D. L. Hurd, J. J. Kipling, Eds., The Origins and Growth of Physical Science, Vol. 2, Pelican Books: Baltimore, MD, 1964, pp. 81 – 100.

23

D. I. Mendeleev, La loi périodique des elements chimiques, Le moniteur scientifique, 1879, 21, 693 – 737.

24

D. L. Mendeleev, ’The Periodic Law of the Chemical Elements, Chem. News, 1879, 40, 231 – 232,243 – 244, 255 – 256, 267 – 268, 279 – 280, 291 – 292, 303 – 304; Ibid, 1880, 41, 2 – 3, 27 – 28, 39 – 40, 49 – 50, 61 – 62, 71 – 72, 83 – 84, 93 – 94, 106 – 108, 113 – 114, 125 – 126.

25

B. Harrow, Eminent Chemists of Our Time, 2nd ed., Van Nostrand, New York, NY, 1927, p. 273.

26

D. M. Knight, Ed., Classical Scientific Papers: Chemistry, Second Series, American Elsevier: New York, NY, 1970, pp. 273 – 309.

1

Dmitri Mendeleev

On the Relation of the Properties to the Atomic Weights of the Elements

[Zeitschrift für Chemie, 1869, 12, 405 – 406]

IF one arranges the elements in vertical columns according to increasing atomic weight, such that the horizontal rows contain analogous elements, also arranged according to increasing atomic weight, one obtains the following table, from which it is possible to derive a number of general deductions:

1. When arranged according to the magnitude of their atomic weights, the elements display a step-like [stufenweise] alteration in their properties.

2. The atomic weights of chemically analogous elements either have similar values (Pt, Ir, Os) or increase in a uniform fashion (K, Rb, Cs).

3. The arrangement according to atomic weight corresponds to the valencies of the elements and, to a certain degree, to differences in their chemical behavior, e.g., Li, Be, B, C, N, 0, F.

4. The elements most widely dispersed in nature have small atomic weights, and all such elements distinguish themselves by their sharply defined characters. They are therefore typical elements and, with justification, the lightest element, H, may be chosen as the typical standard.

5. The magnitude of the atomic weight determines the properties of the element; consequently in the study of compounds one must take into account not only the number and properties of the elements and their reciprocal interactions, but also the atomic weights of the elements. Thus the compounds of S and Te, Cl and I display many analogies, however conspicuous their differences.

6. It allows one to foresee the discovery many new elements, e.g., analogs of Si and Al with atomic weights between 65 and 75.

7. It is to be expected that some atomic weights will require correction, e.g., Te cannot have an atomic weight of 128, but rather one between 123 and 126.

8. The above table suggests new analogies between elements. Thus Bo(?) [U] appears as an analog of Bo and Al, which, as is well-known, has long been firmly established by experiment.

2

Dmitri Mendeleev

On the Correlation Between the Properties of the Elements and their Atomic Weights

[Zhurnal Russkoe Fiziko-Khimicheskoe Obshchestvo, 1869, 1, 60 – 77]

IN the course of the development of our science, the systematic classification of the elements has undergone manifold and repeated changes. The most common classification of the elements into metals and nonmetals is based on physical differences as they are observed in the simple substances, as well as upon differences in the character of the corresponding oxides and other compounds. However, what at first glance appeared to be unambiguous, lost its importance entirely when more detailed knowledge was obtained. Ever since it became known that an element, such as phosphorus, can exist in nonmetallic as well as in metallic form, it became impossible to base a classification on physical differences. Even the formation of basic and acidic oxides does not provide a reliable guide, since, between the definitely basic and definitely acidic oxides, there exists an entire series of transitional forms, among which must be included the oxides of bismuth, antimony, arsenic, gold, platinum, titanium, boron, tin, and many other elements. Moreover, the analogies between the compounds of such metals as bismuth, vanadium, antimony, and arsenic and those of such nonmetals as phosphorus and nitrogen, or between those of tellurium and the compounds of selenium and sulfur, or between those of silicon, titanium, and zirconium and the compounds of tin, no longer permit a distinction between metals and nonmetals for purposes of classifying the simple substances. The study of organometallic compounds, which has demonstrated that sulfur, phosphorus, and arsenic form compounds of the same kind as mercury, zinc, lead, and bismuth, conclusively confirms the validity of the above conclusion.

Likewise, those systems of simple substances based on behavior with respect to hydrogen and oxygen show many uncertainties and separate elements that, without doubt, exhibit great similarity. So far, bismuth has not been combined with hydrogen as have the elements similar to it. Nitrogen, which resembles phosphorus, forms extraordinarily unstable oxides and, in contrast to phosphorus, does not directly oxidize. Iodine and fluorine are clearly distinguished from each other by the fact that iodine readily forms compounds with oxygen but reacts with hydrogen only under extreme conditions, whereas fluorine has not yet been combined with oxygen (most often it displaces oxygen) but does form a very stable compound with hydrogen. Magnesium, zinc, and cadmium, which form such a natural group of simple substances, would also, according to this system, belong to different groups, as would copper and silver. On the same grounds, thallium would be separated from the related alkali metals, and lead from barium, strontium, and calcium. Even the simple substances forming the most natural of groups – such as palladium, rhodium, ruthenium, on the one hand, and osmium, iridium, and platinum, on the other – would be assigned to widely separated places in this system.

The ordering of the elements according to their electrochemical character is considered by the history of chemistry to be as unfortunate an attempt as is their ordering according to their relative affinities. Because of the diversity of the relations existing between the simple substances, one cannot think of representing their system in the form of a continuous series, since the mutual relations of the substances are extraordinarily diverse. If the substances are ordered according to their affinities or according to the electrical sequence, then one involuntarily leaves out of consideration the reversibility of reactions, which represents an essential property of chemical behavior. If zinc decomposes water (forming zinc oxide and releasing hydrogen), then hydrogen also decomposes zinc oxide. Chlorine displaces oxygen but oxygen does the same with chlorine, as we see from the synthesis of chlorine, for this reaction consists in the oxidation of hydrochloric acid. This fact is completely left out of consideration by those who desire to arrange the elements in a continuous series.

In recent times, the majority of chemists is inclined to achieve a correct ordering of the elements on the basis of their valency. In principle, this trend is very uncertain. This doctrine was called for by the investigation of organometallic compounds, by applying to them the law of paired atom numbers and the general concept of the limits of chemical compounds, and by the endeavor to circumvent the versatile theory of types. These relations have little or no application to the compounds of other elements. Nitrogen, for example, forms many compounds with unpaired atom numbers, as does mercury. Elements, such as vanadium, molybdenum, tungsten, manganese, chromium, uranium, arsenic, antimony, and the elements of the platinum group, form compounds with variable valencies which are so characteristic and which resemble so little the ideas we gain from an acquaintance with organic compounds that it is impossible, at least for the present, to think that we can make use of the strict concept of valency in order to understand the compounds of these elements. For aluminum, compounds which contain one atom of this element are totally unknown; for copper and mercury, the suboxides, in which these elements are monovalent, represent, in many regards, far more stable compounds than do the oxides. Thus, these elements – similar to silver – are monovalent elements with respect to the salts of their suboxides but, with respect to the salts of their oxides, they are divalent. Lead appears in its organometallic compounds as a tetravalent element, while its mineral compounds lead us to regard it as a divalent element. Iodine is a trivalent element in a certain sense, phosphorus is both tri- and pentavalent. For the determination of the valency of elements, one must come to a conclusion on the basis of the molecular composition of arbitrarily chosen compounds. If, for example, in the case of copper, cupric chloride is chosen as the saturated compound, then it appears that this saturated copper compound is a very unstable substance which easily changes into an unsaturated compound, namely cuprous chloride, in which copper is a monovalent element. But when one chooses the highest, albeit less stable, compounds as a measure for valency, then doubts regarding even the valency of hydrogen may arise – thus hydrogen peroxide represents a compound of one atom of hydrogen with one atom of oxygen similar to cupric and mercuric oxide. In this event, arsenic, phosphorus, and nitrogen, antimony and others have to be regarded as pentavalent and even as heptavalent elements; iodine (because of its compounds with chlorine) must be regarded as a tri- or pentavalent element, and perhaps of even still higher valency. Then it is nearly impossible to determine the valency of elements such as manganese and aluminum. Potassium permanganate, which exhibits an analogy with potassium chlorate, is of such importance in the problem of valency that either manganese must appear as a monovalent element, like chlorine, or chlorine must be accepted as a di-, tetra-, or hexavalent element like manganese.

Thus one must assume that oxygen compounds cannot serve as a guiding principle for the determination of the valencies of the elements, because, according to this theory, an indeterminately large quantity of oxygen may combine with other substances (since it can always be squeezed between two elements). Besides, the following would prove to be totally inexplicable: the valence of many elements; the analogy which has been put forward in inorganic chemistry between the corresponding compounds of chlorine and oxygen; and the fact that the accumulation of oxygen has a definite limit, as we see for the formation of many oxygen salts, which usually contain no more than four oxygen atoms (for example, the salts of perchloric acid, MClO4; the salts of sulfuric acid, M2SO4; the salts of phosphoric acid, M3PO4; the salts of arsenic acid, molybdic acid, tungstic acid, chromic acid, permanganic acid, and an entire series of other acids). The fact that oxygen compounds with the least amount of oxygen are often less stable than those which contain more oxygen, as, for example, with the oxygen compounds of Cl, Mn, etc., would remain unexplained. That it is correct to consider the principle of valency as uncertain in its application to the system of elements may also be seen from the fact that, so far, not a single rigorous system has been constructed in this direction, and also from the fact that, for this system, elements, such as silicon and boron, must be widely separated, as is the case for silver, copper and mercury, antimony and bismuth, thallium and cesium. On the other hand, the law of paired atom numbers, which forms such an important principle in the study of all organic compounds, proves not to be universal, and could, in my opinion, be compared with the symmetry law of crystalline forms. In the majority of such forms, each crystal face has its corresponding parallel face. One could deduce from this that forms in which no such parallel faces are at hand cannot occur. More intimate knowledge of the subject reveals, however, the existence of such forms – in tetrahedrons there exists symmetry, though they display no parallel faces. The same thing could be applied to the number of atoms. The even number of atoms for the known elements would represent a case of obvious and clear symmetry, the opposite a more rare case, similar to the hemihedral form. As far as the changes in the doctrine of the valency of the elements are concerned, in so far as they tend to recognize the variability of valence, they can only serve as the best proof that the doctrine is untenable. If carbon may be tetra- or divalent, if copper and mercury may occur as divalent and monovalent, if phosphorus may be penta-, tri- or divalent, then why should one not also admit that hydrogen and chlorine may be mono-, di-, tri-, etc. valent? Naturally, in this case, no difficulties would arise regarding the explanation for the existence and structure of any arbitrary compound, though, of course, there would also be no firm basis for criticizing it.