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Q. What is the basis of a periodic table?
A. Mendeleyev, introducing his periodic table to the Russian Chemical Society in 1869, began by explaining, "The elements, if arranged according to their atomic weights, exhibit an evident periodicity of properties." Later "weights" were replaced by "masses", which have been replaced by "atomic numbers." In more general terms, the 2008 Wikipedia guide is "..certain properties of elements repeat periodically when arranged by atomic number." (details)
Q. Did Mendeleyev make the first periodic table?
A. No. Alexandre Beguyer de Chancourtois' "telluric screw" was the first, as he proposed a classification of the then-known (1858) elements based on atomic weights, and plotted them on the surface of a cylinder, in a spiral. (details)
Q. Why does Mendeleyev get the credit?
A. Thirteen years after the "telluric screw", and generally in parallel with Lothar Meyer’s work, Mendeleyev - not initially having had the benefit of seeing de Chancourtois’ 3D arrangement - proposed an improvement of an earlier flat table. It had eight groupings, with gaps carefully arrived at related to the properties of adjacent elements. His fame was assured when these gaps were later filled by others with previously undiscovered elements fitting his descriptions.. (details)
Q. Is his table the familiar one?
A. No. there were shifts of his 8th column elements into another column, and a column (now called group) of gases added. The common flat form has been developed with adaptations by Bayley, then Werner, Moseley, and finally, Glenn Seaborg. (details)
Q. What did Seaborg do to the periodic table?
A. During his work on the atomic bomb during WWII, he and his group at Fermi Labs discovered numerous new elements. Insertion into the periodic table made the result too wide for convenience, so he proposed removal of these Rare Earths from inside the table to a position below the remainder of the elements, under the Lanthanides. (details)
Q. What other locations for elements are in question?
A. Hydrogen placement is problematic. Noted chemists and science philosophers are divided as to whether the H data should be placed in a box over Li, F, C, or no one group. the criteria vary, from atomic number triads, to electronic configurations, to ionization energy, both for H and He, and likely for others as well. (details)
Placement of exit/re-entry points of the Rare Earths are also in dispute, some leaving a blank on the flat chart below Sc & Y, others putting La & Ac there, and some promoting Lu & Lr for that spot. (details)
Q. What is currently considered an "alternative periodic table" ?
A. Any arrangement of element symbols and information, either 2 or 3 dimensional, not graphically represented in a flat grid such as that approved by the International Union of Pure and Applied Chemistry (IUPAC). (details)
Q. Why do we need static charts and models when the Internet is full of interactive ones?
A. One answer is its convenience and low cost due to mass production. Static charts require only the pages upon which they are printed rather than a computer and the Internet. A printed chart can show every element at once, and is on a wall in virtually all science classrooms worldide, they are in all chemistry books, and can be folded up and carried in a pocket. (details)
Q. Why do we need 3-D models when flat charts are so handy to use?
A. Most 3-D models are intended to show new students the correct unbroken numerical sequence of the elements, allowing the learner to stay on track while tracing trends, similarities, or differences for any element, clarifying the relationships of the elements for beginners at any educational level.
As in the study of geography, where the globe introduces the concept followed by flat maps to permit closer examination of places on the globe - however distorted they must become - the 3-D chart avoids distortions necessary to transfer the natural element relationships to a flat surface, easing the learner into future use and credibility of flat periodic tables. They also provide more motivational, interesting - and interactive - educational possibilities, while also appealing to a wider range of intellectual types. (details)
