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The periodic Table of the Elements. by Andrei Nesterovitch, Biology Department, Stephen F. Austin State University. BTC 575 Instructor – Dr. A. Van Kley. Introduction.
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The periodic Table of the Elements by Andrei Nesterovitch, Biology Department, Stephen F. Austin State University. BTC 575 Instructor – Dr. A. Van Kley
Introduction 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 realized 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.
Introduction 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.
Introduction 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.
By the end of the 1700s only about 30 elements had been identified. These elements were mostly metals such as copper, silver and gold that had been known and used for currency and jewelry since prehistoric times. History By the early 1800 scientists were using new laboratory technique to discover new elements. In less than 100 years scientists doubled the number of known elements.
History Döbereiner, Johann (1780-1849) In the early 1817 Johann Dobereiner found that barium, calcium and strontium had very similar properties. He put these elements together in groups called a triad. He also put the elements in order according to their masses. He found that the middle elements in each group had a mass that is about half way between the other two. Dobereiner found several groups of three that worked together in the same way. This was the beginning of looking for trend in the arrangements of elements.
History Döbereiner, Johann (1780-1849) 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 Handbook der Chemie , three tetrads and even a pentad - nitrogen, phosphorus, arsenic, antimony and bismuth - which we now recognize as group 15 of the p-block of the periodic table.
History Stanislao Cannizzaro (1826–1910) 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 (fellow of Amadeo Avogadro) in 1858. Prior to this, equivalent weights were used and for many elements there were several equivalent weights, depending upon the elements oxidation state.
History Béguyer de Chancourtois (1820–1886) Béguyer de Chancourtois (French geologist) 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”.
History Béguyer de Chancourtois (1820–1886) 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.
History Newlands, John (1837-1898) In 1863, almost 50 years after Doberiner developed his triad John Newlends (Professor of Chemistry at the School of Medicine for Women, London) developed a new method for organizing elements. In those 50 years science has progressed and more elements were known. Newlands took Doberieners basic ideas and expanded on them. He organized his elements by mass and property too, but he added a twist. Dobereiner had work only in small groups, but Newlands wanted to relate all the elements to each other. He discovered a repetition in the properties of elements.
History Newlands, John (1837-1898) 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.
History Newlands, John (1837-1898) 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 criticized, 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 Metal.
History Julius Lothar Meyer (1830–1895) 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.
History Julius Lothar Meyer (1830–1895)
History Julius Lothar Meyer (1830–1895) 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.
History Julius Lothar Meyer (1830–1895) 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 discovery 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.
Mendeleev’s discovery 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 realized that he had discovered, rather than designed, the periodic table is shown by his attitude towards it.
Mendeleev’s discovery 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 5.9 g cm -3.
Mendeleev’s discovery 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.
The biography of D. Mendeleev Born in Tobolsk (Siberia) he was youngest of 14 children. His father was the Principal of a gymnasium. Mother was the exceptional member of the faimily: A brilliant and beautiful woman self educated by studying all of her brother's stuff (who did attend university) - very prominent siberian family published the first newspaper in Siberia. In 1848 his father died, and Mendeleev and mother walk 1000 miles to Moscow to get Dimitry into the University.
The biography of D. Mendeleev He was not admitted and he and his mother then walked to St Petersburg where he did get into the institute of Pedagogy in 1860. In 1869 he received a government grant to go and get his Ph.D in Paris with the Physicist Renault. He became Professor of General Chemistry at the University of Petrograd (St. Petersburg) in 1866.
The biography of D. Mendeleev In 1893 he was asked to head up the Bureau of Weights and Measures. Accepted and did a marvelous job. Died in 1907 of influenza. Published over 262 papers on virtually everything and many huge books and treatises.
