Can some one explain the early development of the periodic table?

Answer 1

Someone just made rows and columns and filled them in. Only later did they have them printed up for people to use.

Answer 2

No chemistry textbook, classroom, lecture theatre or research laboratory is complete without a copy of the periodic table of the elements. Since the earliest days of chemistry, attempts have been made to arrange the known elements in ways that revealed similarities between them. However, it required the genius of Mendeleev to see that arranging elements into patterns was not enough; he realised that there was a natural plan in which each element has its allotted place, and this applies not only to the known elements but to some that were still undiscovered. Today we have the so-called long form of the table. This has emerged supreme from well over 100 designs that have been proposed since the time of Mendeleev. With the advantage of hindsight we can now see why this form of the table was bound to succeed.

Today there are 111 elements recognised by IUPAC, and these are usually displayed in the form of a matrix called a periodic table. The term periodic came from the regular occurrence of certain chemical properties in the list of known elements when these are arranged in order of increasing relative mass. The common form, complete with the new group numbers (1-18) were finally agreed by the International Union of Pure Applied Chemistry, IUPAC, in 1985, after years of wrangling. In truly Parkinsonian fashion, this least important of changes has probably consumed the most effort!

Since Antoine Lavoisier first defined a chemical element and drew up a table of 33 of them for his book 'Traité Elémentaire de Chimie' (Treatise on the Chemical Elements) published in 1789, there have been attempts to classify them. Lavoisier himself grouped them into four categories on the basis of their chemical properties: gases, nonmetals, metals and earths. In the first category he listed substances that we now know as oxides but which at the time had defeated all attempts at separation.

This desire to identify and classify elements continued in chemistry for another 80 years until Mendeleev stumbled upon the correct classification - the periodic table. Today the periodic table is securely based on the properties of atomic number of the nucleus and the electron energy levels which surround it. Both of these concepts postdate Mendeleev by several decades. He, however perceived them indirectly through the related properties of atomic weight and chemical valency and arrived at the periodic table in 1869.

Because atomic weight, relative atomic mass, is roughly proportional to atomic number, and because valency, which manifests itself in the chemical composition, is based on the outermost electrons of an atom, Mendeleev had chosen the two properties that in his day most nearly reflected the fundamental principles on which the table today is based. Consciously or subconsciously, he arrived at the idea that a table existed with positions that were to be occupied by the elements, rather than the other way round - that the known elements determined the arrangement of the table, as others imagined.

This being so, Mendeleev then put the 65 elements he knew into his table and at the same time pointed out the many unoccupied positions in the overall scheme. He took the further and much bolder step of predicting the properties of these missing elements. Moreover, the gap in atomic weights between cerium (140) and tantalum (182) suggested to him that a whole period of the table remained to be discovered. Later in the century many of these elements, which we now call the lanthanides, were isolated.

Historical Background

Mendeleev’s periodic table of 1869 seems all the more remarkable when we consider his relative isolation from the main centres of chemical research in Western Europe, and the rather naive attempts made by scientists in those centres to bring some sort of order to the growing list of chemical elements.

As early as 1829 Johann Döbereiner announced his law of Triads, which referred to groups of three chemically similar elements in which the properties of the middle element could be inferred from the lighter and heavier ones. Such triads as lithium, sodium and potassium, sulfur, selenium and tellurium or chlorine, bromine and iodine are clear examples. By 1843 when Leopold Gmelin published the first edition of his famous Handbuch der Chemie , three tetrads and even a pentad - nitrogen, phosphorus, arsenic, antimony and bismuth - which we now recognise as group 15 of the p-block of the periodic table.

No real progress was going to be made in classifying elements until the one essential property common to them all, their atomic weight, was settled. This was done by Stanislao Cannizzaro in 1858. Prior to this, equivalent weights were used and for many elements there were several equivalent weights, depending upon the elements oxidation state.

Telluric Screw and Law of Octaves

Béguyer de Chancourtois in 1862 was the first person to make use of atomic weights to reveal periodicity. He drew the elements as a continuous spiral around a cylinder divided into 16 parts. The atomic weight of oxygen was taken as 16 and used as the standard against which all others were compared. Chancourtois noticed that certain of the triads appeared below one another in his spiral. In particular the tetrad oxygen, sulfur, selenium and tellurium fell together, and he called his device the “telluric screw”.

The atomic weights of these elements are 16,32,79 and 128, respectively, and quite fortuitously they are multiples or near multiples, of 16. Other parts of the screw were less successful. Thus boron and aluminium come together all right but are then followed by nickel, arsenic, lanthanum and palladium. Chancourtois had discovered periodicity, but had got the frequency wrong. Not bad for a non - chemist - he was a geologist.

Another man who got nearer was John Newlands, Professor of Chemistry at the School of Medicine for Women, London. He chose a table of seven columns and entered his elements in increasing order of atomic weight. This arrangement produced some misalignments, but Newlands was sufficiently secure in his chemical knowledge to put similar elements in the same column even if it meant squashing two elements into some of his boxes. Newlands also recognised silicon and tin as part of a triad and predicted that there would be a missing element intermediate between these, with atomic weight of about 73. This predated Mendeleev’s predictions about germanium (which has an atomic weight of about 72.6) by about five years. However, Newlands did not leave a space for this missing element in his table of 1865. In fact, he left no vacant slots, which reveals that he had no appreciation of looking for an order that transcended his data.

By analogy with the tonic scale of seven musical notes and their octaves, Newlands called his discovery of periodicity the ‘Law of Octaves’. His efforts were criticised, indeed were publicly ridiculed, by members of the chemical fraternity and it was only in 1887, 18 years after Mendeleev’s work that Newlands’s contribution was recognised by the Royal Society, which awarded him the Davy medal.

Other Attempts

Other chemists who were sufficiently intrigued by atomic weights and the periodic occurrence of chemical properties also proposed repeating units of 1 (William Odling, 1864) and 15 (Lothar Meyer, 1868). The first of these, Odling, drew up a table of elements that bears a striking resemblance to Mendeleev’s first table. The groups are horizontal, the elements are in order of increasing atomic weight and there are vacant slots for undiscovered ones. In addition, Odling overcame the tellurium iodine problem, and he even managed to get thallium, lead mercury and platinum in the right groups - something that Mendeleev failed to do at his first attempt. However, we need lose little sleep over Odling’s failure to achieve recognition, since it is suspected that he, as Secretary of the London Chemical Society, was instrumental in discrediting Newlands’s efforts at getting his periodic table published.

The German chemist Julius Lothar Meyer also used Cannizzaro’s atomic weights to draw up a primitive table in 1864, but the more sophisticated version he produced in 1868 for the second edition of his textbook was not used and remained among his papers to be published only after his death in 1895. However, what Meyer did was to publish in 1870 a graph which plotted atomic volumes against atomic weights. This clearly showed the periodic changes of this property, with maximum atomic volumes at intervals of 7, 7, 14 and 15. With the inclusion of undiscovered elements this graph would have revealed the observed intervals of 8, 8, 18 and 18 of the first four rows of the modern table.

Meyer published too late to claim priority over Mendeleev but just in time to confirm that the latter’s discovery of the periodic table was based on sound chemical principles. Although Mendeleev published his tables in the new and obscure journal of the Russian Chemical Society, his paper was abstracted within weeks of its appearance into the German journal Zeitschrift für Chemie, and well before Meyer’s paper was published in December of that year, 1869.

Mendeleev’s Genius

What then did Dimitri Ivanovich Mendeleev do that sets his table apart from those earlier tables? The height of his achievement can partly be judged by the depths from which he started. Born in Tobolsk in Western Siberia in 1834, the youngest of 14 children, whose father became blind and died of tuberculosis the year Dimitri finished school, Dimitri was his mother’s favourite and she did all she could to further his education. After graduating from the Central Pedagogic Institute of St Petersburg, Dimitri went on to do research in Paris and Heidelberg for two years, before returning in 1861 to St Petersburg, where he eventually became professor of general chemistry in 1867.

He began writing a textbook of inorganic chemistry, 'Principles of Chemistry', which eventually ran into many editions and translations. In organising the material for this work, he grouped elements into chapters according to their valency. While in Germany, Mendeleev had learned of Cannizzaro’s atomic weights, and he used these to arrange the elements in ascending order.

The fateful day for Mendeleev was 17 February 1869 (Julian calendar). He cancelled a planned visit to a factory and stayed at home working on the problem of how to arrange the chemical elements in a systematic way. To aid him in this endeavor he wrote each element and its chief properties on a separate card and began to lay these out in various patterns. Eventually he achieved a layout that suited him and copied it down on paper. Later that same day he decided a better arrangement was possible and made a copy of that, which had similar elements grouped in vertical columns, unlike his first table, which grouped them horizontally. These historic documents still exist.

That Mendeleev realised that he had discovered, rather than designed, the periodic table is shown by his attitude towards it. First, he left gaps in it for missing elements. Leaving such gaps in tables of elements was not in itself new, but Mendeleev was so sure of himself that he was prepared to predict the physical and chemical properties of these undiscovered elements. His most notable successes were with eka aluminium (= Gallium) and eka-silicon (= germanium). Lecoq de Boisbaudran discovered gallium in 1875 and reported its density as 4.7g cm -3, which did not agree with Mendeleev’s prediction of 5.9g cm -3. When he was told that his new element was Mendeleev’s eka-aluminium, and had most of its properties foretold accurately, Boisbaudran redetermined its density more accurately and found it to be as predicted, 5.956 g cm -3. There could be no doubt now that Mendeleev had discovered a fundamental pattern of Nature.

Secondly, Mendeleev was prepared to place elements in his table in apparently the wrong group. Thus the oxide of beryllium had been reported to be Be2O3 by none other than the great chemist Berzelius. Later workers claimed it to be BeO. The former gave the element a valency of III, the latter II. Mendeleev had a vacancy in his table for an element in group II, and so he had no hesitation in placing beryllium in it.

Thirdly, Mendeleev was prepared to place elements in his table in the wrong order of atomic weight. The anomaly here was that tellurium (atomic weight 128) should come after iodine (127), whereas the group for Te is clearly the one before I. Mendeleev presumed that the atomic weight of Te had been determined wrongly. However, fresh analyses confirmed the original value and this anomaly remained as a puzzle for chemists until the discovery of isotopes. Where I has only a single isotope of mass number 127, Te has eight stable isotopes of mass numbers 120 to 130, and the most abundant is 130Te (32%). This results in the high average atomic weight of 128.