A periodic table for molecules.A periodic table for molecules Back in the 19th century, D.I. Medeleevsystematized chemical knowledge of his day by drawing up the periodic table of elements. By arranging the elements according to according to prep. 1. As stated or indicated by; on the authority of: according to historians. 2. In keeping with: according to instructions. 3. two properties, atomic number atomic number, often represented by the symbol Z, the number of protons in the nucleus of an atom, as well as the number of electrons in the neutral atom. Atoms with the same atomic number make up a chemical element. and chemical valence Valence, city, France Valence (väläNs`), city (1990 pop. 65,026), capital of Drôme dept., SE France, in Dauphiné, on the Rhône River. , he could show why elements come in families that make compounds preferentially with certain other families. Later work showed how Mendeleev's periodic arrangement arises from the electronic properties of atoms and so is the key to an understanding of basic chemistry. Now, Mendeleev's work is being extendedto molecules, Ray Hefferlin of Southern College in Collegedale, Tenn., told last week's San Francisco San Francisco (săn frănsĭs`kō), city (1990 pop. 723,959), coextensive with San Francisco co., W Calif., on the tip of a peninsula between the Pacific Ocean and San Francisco Bay, which are connected by the strait known as the Golden meeting of the American Physical Society The American Physical Society was founded in 1899 and is the world's second largest organization of physicists. The Society publishes more than a dozen science journals, including the world renowned Physical Review and Physical Review Letters, and organizes more than twenty science and the American Association of Physics Teachers The American Association of Physics Teachers was founded in 1930 for the purpose of "dissemination of knowledge of physics, particularly by way of teaching."[1] There are more than 10,000 members that reside in over 30 countries. . Work at Southern College since 1977has shown that the periodic law applies at least to molecules made of two atoms. Their chemical properties can be predicted, and they form periodic families just as the elements do. On Mendeleev's chart each elementhas a location in a specific row and column, and that location determines what it does chemically. Mendeleev's chart, having only two dimensions, could be drawn on a sheet of paper. But for two-atom molecules, four dimensions are required -- the row and column addresses of each atom in the molecule. A four-dimensional chart cannot be drawn on paper with any ease, although Hefferlin says his students have produced some interesting computer projections to visualize it. Hefferlin says the project is ideal workto do at an undergraduate college without sophisticated experimental equipment and with undergraduate students who are not experienced in advanced research techniques. It requires collecting and correlating a lot of data on chemical properties of compounds and involves a lot of hand calculation and computer feeding. One important thing about a computermemory is that, unlike the human eye, it does not care how many dimensions there are. If the same periodic principle applies to three-and four-atom molecules as to those with two, it will presumably pre·sum·a·ble adj. That can be presumed or taken for granted; reasonable as a supposition: presumable causes of the disaster. involve even more dimensions. The researchers at Southern College are now working on them. |
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