Chemical Elements Chart History, Part 2 of 2

(History of the Chemical Elements Table)

The Periodic Table of Chemical Elements Originated about 200 Years Ago!

The Modern Periodic Table

  • Chemist Julius Lothar Meyer of Breslau University in Germany, while in the process of revising his chemistry textbook in 1868, produced a periodic table that turned out to be remarkably similar to Mendeleev's famous 1869 version; although Lothar Meyer failed to classify all the elements correctly.
  • Unlike his predecessors, Mendeleev had sufficient confidence in his periodic table to use it to predict several new elements and the properties of their compounds.

  • The table did not appear in print until 1870 because of a publisher's delay; a factor that contributed to an acrimonious dispute for priority that ensued between Lothar Meyer and Mendeleev.
  • Around the same time, Mendeleev assembled his own periodic table while he, too, was writing a textbook of chemistry.
  • Unlike his predecessors, Mendeleev had sufficient confidence in his periodic table to use it to predict several new elements and the properties of their compounds.
  • He also corrected the atomic weights of some already known elements.
  • Interestingly, Mendeleev admitted to having seen certain earlier tables; such as, those of Newlands, but claimed to have been unaware of Lothar Meyer's work when developing his chart.
  • Although the predictive aspect of Mendeleev's table was a major advance, it seems to have been overemphasized by historians, who have generally suggested that Mendeleev's table was accepted especially because of this feature.
  • These scholars have failed to notice that the citation from the Royal Society of London that accompanied the Davy Medal (which Mendeleev received in 1882) makes no mention whatsoever of his predictions.
  • Instead, Mendeleev's ability to accommodate the already known elements may have contributed as much to the acceptance of the periodic system as did his striking predictions.
  • Although numerous scientists helped to develop the periodic system, Mendeleev receives most of the credit for discovering chemical periodicity because he elevated the discovery to a law of nature and spent the rest of his life boldly examining its consequences and defending its validity.
  • Defending the periodic table was no simple task because its accuracy was frequently challenged by subsequent discoveries.
  • One notable occasion arose in 1894, when William Ramsay of University College London and Lord Rayleigh (John William Strutt) of the Royal Institution in London discovered the element argon; over the next few years, Ramsay announced the identification of four other elements: helium, neon, krypton and xenon; known as the noble gases.
  • The last of the known noble gases, radon, was discovered in 1900 by German physicist Friedrich Ernst Dorn.
  • The name "noble" derives from the fact that all these gases seem to stand apart from the other elements, rarely interacting with them to form compounds.
  • As a result, some chemists suggested that the noble gases did not even belong in the periodic table.
  • These elements had not been predicted by Mendeleev or anyone else, and only after six years of intense effort could chemists and physicists successfully incorporate the noble gases into the table.
  • In the new arrangement, an additional column was introduced between the halogens (the gaseous elements fluorine, chlorine, bromine, iodine, and astatine) and the alkali metals (lithium, sodium, potassium, rubidium, cesium, and francium).
  • A second point of contention surrounded the precise ordering of the elements.
  • Mendeleev's original table positioned the elements according to atomic weight, but in 1913, Dutch amateur theoretical physicist Anton van den Broek suggested that the ordering principle for the periodic table lay instead in the nuclear charge of each atom.
  • Understanding the Atom

  • The periodic table inspired the work not only of chemists but also of atomic physicists struggling to understand the structure of the atom.
  • In 1904, working at Cambridge, physicist J. J. Thomson (who also discovered the electron) developed a model of the atom, paying close attention to the periodicity of the elements.
  • The periodic table inspired the work not only of chemists but also of atomic physicists struggling to understand the structure of the atom.

  • He proposed that the atoms of a particular element contained a specific number of electrons arranged in concentric rings.
  • Furthermore, according to Thomson, elements with similar configurations of electrons would have similar properties; Thomson's work thus provided the first physical explanation for the periodicity of the elements.
  • Although Thomson imagined the rings of electrons as lying inside the main body of the atom, rather than circulating around the nucleus as is believed today, his model does represent the first time anyone addressed the arrangement of electrons in the atom, a concept that pervades the whole of modern chemistry.
  • Danish physicist, Niels Bohr, the first to bring quantum theory to bear on the structure of the atom, was also motivated by the arrangement of the elements in the periodic system.
  • In Bohr's model of the atom, developed in 1913, electrons inhabit a series of concentric shells that encircle the nucleus.
  • Bohr reasoned that elements in the same group of the periodic table might have identical configurations of electrons in their outermost shell and that the chemical properties of an element would depend in large part on the arrangement of electrons in the outer shell of its atoms.
  • Bohr's model of the atom also served to explain why the noble gases lack reactivity: noble gases possess full outer shells of electrons, making them unusually stable and unlikely to form compounds.
  • Indeed, most other elements form compounds as a way to obtain full outer electron shells.
  • More recent analysis of how Bohr arrived at these electronic configurations suggests that he functioned more like a chemist than has generally been credited.
  • Bohr did not derive electron configurations from quantum theory but obtained them from the known chemical and spectroscopic properties of the elements.
  • Quantum mechanics can only reproduce Mendeleev's original discovery by the use of mathematical approximations; it cannot predict the periodic system.
  • Variations on a Theme

  • After evolving for over 200 years through the work of many people, the periodic table remains at the heart of the study of chemistry.
  • It ranks as one of the most fruitful ideas in modern science, comparable perhaps to Charles Darwin's theory of evolution.
  • Unlike theories such as Newtonian mechanics, it has not been falsified or revolutionized by modern physics but has adapted and matured while remaining essentially unscathed.

  • —Compiled from a summary of
    "The Evolution of the Periodic System From its origins some 200 years ago,
    the periodic table has become a vital tool for modern chemists" by Eric R. Scerri;
    as seen in the Scientific American; September, 1998; pages 78-83.

    The knowledge in this article is applicable to the Chemical Elements List where you will find considerable information about their histories and other facts.

    Chemical Elements Chart History, Part 1 of 2 is available here, if you want it again.