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History of the Periodic Table

History of the Periodic Table

Author: Michael Geyer
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"The periodic table of the elements is one of the most powerful icons in science: a single document that captures the essence of chemistry in an elegant pattern. Indeed, nothing quite like it exists in biology or physics, or any other branch of science, for that matter." The periodic table is "a tool that serves to organize the whole of chemistry." Eric R. Scerri

Although Dmitri Mendeleev is often considered the "father" of the periodic table, the work of many scientists contributed to its present form. This Sophia lesson will attempt to summarize the major milestones in the development of this tool.

All text for this activity is taken from the book "The Periodic Table: Its Story and Its Significance" by Eric R. Scerri, Oxford University Press, ©2007. {Link to book}

Scerri, E. (2007). The periodic table: Its story and its significance. Oxford: Oxford University Press. ISBN 0-19-530573-6.

Johann Wolfgang Döbereiner (1817)

In 1817 Johann Döbereiner was the first to notice the existence of various groups of three elements, subsequently called triads, which showed chemical similarities and which displayed an important numerical relationship, namely, that the weight of the middle element was the approximate average of the values of the two elements flanking it in the triad. His first triad included calcium, strontium, and barium. He required that, in order to be meaningful, his triads should reveal chemical relationships among the elements as well as numerical relationships. This observation had little impact on the chemical world at first, but later became very influential.

In 1829 he added three new triads to his discovery.

  • chlorine, bromine, iodine
  • sodium, lithium, potassium
  • sulfur, selenium, tellurium

{pg. 42-43}

Leopold Gmelin (1843)

Although Döbereiner is rightly regarded as the originator of the notion of triads, Gmelin also did much useful work in this area, and it was he who coined the term "triad." Like Döbereiner, Gmelin considered both chemical and numerical relationships when looking for triads, and he was able to extend his predecessor's work using improved atomic weights that had been unavailable to Döbereiner. For example, whereas Döbereiner had grouped magnesium together with the alkaline earth elements based on their chemical similarities, he was unable to find a triad relationship involving it and the other alkaline earth elements. Gmelin, on the other hand, was able to discern a relationship using his own newly obtained values for atomic weights.

But one of the more remarkable aspects of Gmelin's work was a system of arranging the elements. From the existence of four unconnected triads discovered by Döbereiner, Gmelin was able to make a huge leap forward in obtaining a system based on triads consisting of as many as 55 elements. In addition, his system as a whole was essentially ordered according to increasing atomic weight (although it was not explicitly arranged that way). With this work, Gmelin succeeded in capturing the correct grouping of most of the then known main-group elements. Gmelin arranged his triads horizontally in a V-shaped schematic.

When Gmelin published his new arrangement of the chemical elements, he was possibly the first chemistry textbook author to use his system as the basis for how he presented the information in his chemical textbook.

{pg. 44-46}

Alexandre Emile Béguyer de Chancourtois (1862)

In 1862 de Chancourtois published his telluric screw, or his system of arranging the known chemical elements. He proposed a three-dimensional representation of the elements arranged according to what he termed increasing "numbers" along a spiral. This table is a short-form table that does not separate main-group elements from transition metals.

De Chancourtois' published telluric screw.

A simplified diagram explaining De Chancourtois' telluric screw.

He was the first to recognize that the properties of the elements are a periodic function of their atomic weights. Although he hit upon this crucial notion underlying the periodic system, de Chancourtois' system did not create much impression on chemists and he is not generally accorded very much credit for several reasons. First, his original publication did not include a diagram, mainly because of the complexity faced by the publisher in trying to reproduce it. Second, his system included some ions, compounds, and alloys. Also, his publication did not appear in a chemistry journal (it was published in the journal of the Académie des Sciences, Comptes Rendus), and he did not develop his insight any further over subsequent years. As a note, he was frustrated that the journal Comptes Rendus failed to include his diagram, so he had his system republished in 1863. But, because it was published privately, it received even less notice from other scientists than did his original.

{pg. 68-71}

John Alexander Reina Newlands (1863)

In 1863 Newlands published the first of what would be many classification systems for the elements. He had developed his system without the benefit of newer atomic weight values that had been issued following a very important chemistry conference in 1860. His first published article on the classification of the elements had been published anonymously, although he revealed his identity soon afterward in response to criticisms.

In 1864 Newlands published his second article on the classification of the elements. This time he drew on the more correct atomic weights issued in 1860. Less than a month after this system appeared he published a third system, but in this table he included fewer elements (24, plus a space for a new element) and made no mention of atomic weights. This article is nevertheless of considerable merit since Newlands assigned an ordinal number to each of the elements, abandoning the arithmetic progressions in atomic weights that had bedeviled earlier investigators. Newlands simply lined the elements up in order of increasing atomic weight without concern for the values of those weights. The most important thing Newlands did in his third publication on the classification of the elements was to present a periodic system; that is, he revealed a pattern of repetition in the properties of the elements after certain regular intervals. This, of course, is the essence of the periodic law, and Newlands deserves credit for having recognized this fact so early, along with De Chancourtois. Another innovation of Newlands' system in 1864 was the way in which he reversed the positions of the elements iodine and tellurium in order to give precedence to chemical properties over the apparent atomic weight ordering.

In 1865 Newlands developed yet another system, which was a vast improvement on that of the previous year in that he now included 65 elements, in increasing order of atomic weight, while once again using ordinal numbers rather than actual values of atomic weight. He went so far as to draw an analogy between a period of elements and a musical octave, in which the tones display a repetition involving an interval of eight notes. This became known as his "law of octaves."

"If the elements are arranged in the order of their equivalents with a few slight transpositions, as in the accompanying table, it will be observed that elements belonging to the same group usually appear on the same horizontal line. It will also be seen that the numbers of analogous elements differ either by 7 or by some multiple of seven; in other words, members of the same group stand to each other in the same relation as the extremities of one or more octaves in music.... The eighth element starting from a given one is a kind of repetition of the first. This particular relationship I propose to term the Law of Octaves."

This statement marks a rather important step in the evolution of the periodic system since it represents the first clear announcement of a new law of nature relating to their repetition of the properties of the elements after certain intervals in their sequence. Newlands was far more explicit about the existence of a periodic law than was De Chancourtois, who merely mentioned it as a possibility. The law of octaves applies perfectly to the first two periods, excluding the noble gases, which had not yet been discovered. Beyond that, Newlands' periodicities were bound to run into difficulties since the inclusion of the transition metals makes the later periods much longer than 8.

Newlands first announced his law of octaves in a paper delivered to the London Chemical Society in 1866, but to his great misfortune, his insight was poorly received. What Newlands presented was an improved version of his 1865 system (see below). The best known response to Newlands is the much-quoted one of George Carey Foster, who suggested that Newlands might well have obtained a superior classification scheme if he had merely ordered the elements alphabetically according to the first letter of each of their names. Newlands continued to publish work on the periodic system through 1878.

Newlands' Table Presented to the Chemical Society in 1866.

{pg. 72-80}

Julius Lothar Meyer (1864)

Julius Lothar Meyer (1830-1895) German Chemist

Meyer is best remembered for his independent discovery of the periodic system, although more credit is given to Mendeleev.  

In 1864 Meyer published a table of 28 elements arranged in order of increasing atomic weights. Meyer struggled to arrange elements just by atomic weights and recognized the need to organize the elements based on chemical properties as well. In some cases, he seemed to have decided to let chemical properties outweigh the strict atomic weight ordering, which Mendeleev was unable to do. An example of this in in the grouping of tellurium with elements such as oxygen and sulfur, while iodine is grouped with the halogens, in spite of their ordering according to atomic weight. Meyer's organization of the elements in columns (vertical) is similar to some of the groups seen in the modern periodic table.

Another very noteworthy feature of Meyer's table is the presence of many gaps to denote unknown elements. Once again, it appears that the leaving of gaps did not originate with Mendeleev, who was to wait another five years before even venturing to publish a periodic system and eventually making the detailed predictions for which he subsequently became so well known.

Similarities of Meyer and Mendeleev Periodic Tables:

  • Both arranged elements by increasing atomic weights.
  • Both recognized a pattern in properties of the elements when arranged by atomic weights.
  • Both left gaps for undiscovered elements.

{Pg. 92-98}

Dmitri Ivanovich Mendeleev (1869)

Although periodic systems were produced independently by six co-discoverers, Dimitri Mendeleev's system is the one that has had the greatest impact so far. Not only was Mendeleev's system more complete than the others, but he also worked much harder and longer for its acceptance. He also went much further than the co-discoverers by using it to predict the existence of a number of unknown elements.

In 1869 Mendeleev produced the first version of a full periodic table that included most of the known elements. He initially grouped the elements according to how they combined with hydrogen to form compounds, but this did not show any signs of other relationships among the elements. When Mendeleev switched his organization to listing the elements by increasing atomic weights his periodic system seemed to fall into place. In Mendeleev's table he left several vacant spaces specifically anticipating many yet unknown elements. Mendeleev's most famous predictions would be for the elements scandium, gallium, and germanium in which he predicted highly accurate atomic weights and other physical properties.

These bold predictions are what set Mendeleev apart from his competitors. His genius lay in his ability to sift intuitively through the mass of correct and incorrect knowledge of the elements that had been accumulated, to produce a system that was both elegant and durable enough to withstand the chemical and physical discoveries that would follow.

Mendeleev's published periodic system, of 1869.

{pg. 103-106, 123-124}

Henry Gwyn Jeffreys Moseley (1913)

Henry Gwyn Jeffreys Moseley (1887-1915) English Physicist

In 1913 and 1914, Henry Moseley showed that the elements should be ordered according to their atomic number rather than atomic weight.

Moseley's predecessors ordered the periodic table by atomic weight and then assigned each element an arbitrary quantity, called atomic number, based on the order of the elements as they appeared in the periodic table, but without any physical meaning.  

Moseley worked as a research student with Rutherford in Manchester. He first experimented on 14 elements, nine of which, titanium to zinc, formed a continuous series in the periodic table. Moseley discovered a fundamental quantity that increased by regular intervals as he moved through his sequence of elements in the order in which they appeared in the periodic table. He quickly recognized this quantity as the positive charge on the nucleus. After this discovery the atomic number became known as the number of protons in the nucleus. Moseley’s work clearly showed that successive elements in the periodic table have an atomic number greater by one unit. From this fact, Moseley and others could identify which gaps remained to be filled in the periodic system and found there were a total of seven such cases still waiting to be discovered. Unlike previous lists of gaps, this list was now completely definitive and included the precise atomic numbers of the still elusive elements, which were 43, 61, 72, 75, 85, 87, and 91.

Medium-long form periodic table as it looked circa 1915 with seven missing elements between the old boundaries from hydrogen to uranium.

Although the use of atomic numbers did not result in any profound changes to the form of the periodic table, the clarification that Moseley brought to the periodic table solved the lingering problems regarding pair reversals of nickel & cobalts as well as tellurium & iodine, which had plagued Mendeleev throughout his career. His discovery also helped to place the rare earth elements which was one of the most difficult periodic law problems since they were notoriously difficult to separate chemically.

Moseley never witnessed the success of his discovery, because he was killed in the early years of World War I, shot through the head in 1915 by a Turkish soldier during the battle of Gallipoli. He was 27 years old. It is generally believed that had Moseley lived just one more year, he would almost certainly have been awarded a Nobel Prize in 1916 for his discovery of the physical basis of atomic number. Since Nobel prizes are given only to living recipients, that possibility died with Moseley at Gallipoli. The Nobel Prize in Physics in 1916 was not awarded at all.

{pg. 31; 170-173}

Glenn Theodore Seaborg (1945)

Glenn Seaborg (1912-1999) American Chemist

In 1945, Seaborg discovered that a major change was needed in the periodic table. Several elements that had been regarded as belonging to the transition metal family were separated out from the main body of the periodic table to form the lanthanide and actinide series (bottom two rows).

Glenn Seaborg suggested that elements beginning with actinium, number 89, should be considered a rare earth series rather than the previous thought that the rare earth elements began after element 92, uranium. Seaborg's new periodic table suggested that the elements europium (63) and gadolinium (64) should have similar characteristics to undiscovered elements 95 and 96, respectively. As a result, Seaborg succeeded in synthesizing and identifying the two new elements, which were named americium (95) and curium (96).

Glenn T. Seaborg Periodic Table of 1945

Seaborg was the principal or co-discoverer of ten elements:  plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium, and element 106, named seaborgium in his honor.  He is one of only two people to have an element named after them while still alive.

Seaborg points out seaborgium (106) on the periodic table.

"This is the greatest honor ever bestowed upon me--even better, I think, than winning the Nobel Prize," said Seaborg, the co-discoverer of plutonium and nine other transuranium elements. "Future students of chemistry, in learning about the periodic table, may have reason to ask why the element was named for me, and thereby learn more about my work." - Glenn Seaborg

{pg. 21-22, 307}