This makes sense because the structure of the atom was not understood at the time, so the concepts of protons and isotopes had yet to be described. The modern periodic table orders the elements according to increasing atomic number rather than increasing atomic weight. For the most part, this doesn't change the order of the elements, but it's an important distinction between older and modern tables.
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But the influence of these changes on the periodic table has been rather minimal. Despite the efforts of many physicists and chemists, quantum mechanics cannot explain the periodic table any further.
For example, it cannot explain from first principles the order in which electrons fill the various electron shells. Variations on a Theme In more recent times, researchers have proposed different approaches for displaying the periodic system. The same virtue is also seen in a version of the periodic table shaped as a pyramid, a form suggested on many occasions but most recently refined by William B. Jensen of the University of Cincinnati.
Another departure has been the invention of periodic systems aimed at summarizing the properties of compounds rather than elements. This table has enabled scientists to predict the properties of diatomic molecules successfully. In a similar effort, Jerry R. Dias of the University of Missouri at Kansas City devised a periodic classification of a type of organic molecule called benzenoid aromatic hydrocarbons.
The compound naphthalene C10H8 , found in mothballs, is the simplest example. This scheme has been applied to a systematic study of the properties of benzenoid aromatic hydrocarbons and, with the use of graph theory, has led to predictions of the stability and reactivity of some of these compounds.
Still, it is the periodic table of the elements that has had the widest and most enduring influence. After evolving for over years through the work of many people, the periodic table remains at the heart of the study of chemistry.
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. Elsevier, Dennis H. Rouvray in Chemical Intelligencer, Vol. Classification, Symmetry and the Periodic Table.
William B. Jensen in Computing and Mathematics with Applications, Vol. Scerri in Chemistry in Britain, Vol. The Electron and the Periodic Table. Eric R.
Scerri in American Scientist, Vol. He later earned a Ph. Since arriving in the U. In January he will take up a position in the chemistry department at Purdue University.
His e-mail address is scerri bradley. Sign up for our email newsletter. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. In February , while writing the second volume of his chemistry textbook Principles of Chemistry, Mendeleev devised his own form of the periodic table.
Popular accounts tell of Mendeleev shuffling and rearranging cards labeled with the elements and their properties, like a game of solitaire. In , Mendeleev printed copies of his table and sent them to colleagues throughout Russia and Europe. Mendeleev went beyond just creating a table, however; he argued that the organization of elements reflected an underlying periodic law. For example, while Meyer switched the placement of tellurium and iodine, Mendeleev switched them and argued that the atomic mass of one of them had to be wrong.
The atomic masses were not, in fact, wrong, because periodicity turns out to be based on atomic number, not atomic mass. Mendeleev corrected the masses of several elements on the basis of his table, and these corrections were later experimentally validated. While Meyer left gaps in his table, Mendeleev predicted that elements would be discovered that would fill those gaps. This was a bold move; chemists at the time were expected to be reporters of existing facts, not speculators on what might yet be discovered.
At the time, not only was it inconceivable that an element could be nonreactive, but there was no room for them in the periodic table. When the only proposed noble gas was argon, Mendeleev and other chemists argued that it was not a new element but triatomic nitrogen N 3. After the discovery of helium, krypton, neon, and xenon, however, these inert gases couldn't be explained away.
The road to our modern-day periodic table was winding, full of dead ends and wrong turns. It required numerous discoveries, scientists, and experiments, as well as numerous failures and triumphs. It was, essentially, typical of science. Mendeleev, Meyer, and the others were indeed incredible scientists, not because they figured everything out themselves, but because they were fully enmeshed in the illustrious enterprise we call science.
Julianna Poole-Sawyer studied molecular biology at Princeton University and the history and philosophy of science at the University of Notre Dame. Akeroyd, F. Gordin, M. New York: Basic Books. Scerri, E. Oxford: Oxford University Press.
Prediction and the Periodic Table. Assembling the Modern Periodic Table The messy road to periodic chemistry. By Julianna Poole-Sawyer. To add even more confusion, in Prussian scientist Alexander von Humboldt and French scientist Joseph Louis Gay-Lussac determined that two volumes of gaseous hydrogen always combined with one volume of gaseous oxygen to form two volumes of water vapor.
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