the Periodic Law of Dmitri Mendeleev
modeled by the Chemical Element System
in the format of the Alexander Arrangement of Elements

CES model
Following de Chancourtois' and Mendeleev's publishing their element arrangements, Mendeleev formulated the Periodic Law in 1869, formalizing the rules they both recognized.
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Other scientists had previously identified periodicity of elements, and Alexandre-Emile Béguyer de Chancourtois, seven years earlier, had arranging the elements then known in a helix, in three-dimensional barber pole style.
Vis Tellurique museum exhibit

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The word periodic means occurring or repeating at intervals. So the periodic law states that the chemical properties of the elements occur periodically when the elements are arranged in order - in the mid-1800s - of increasing weight. For example, in a column (family or group) of elements, the elements will have similar chemical properties because the chemical properties are repeating at intervals along the element line.
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Periodic Law card included with 3D Forever
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Carmen Giunta's translation of Mendeleev's words are: "The elements, if arranged according to their atomic weights, exhibit an evident stepwise variation of properties.", but other experts translate 'stepwise' as the intended 'periodicity', a more appropriate term.
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For over a century and a half, regardless of many different attempts to improve the relation between the Periodic Law and the tabular format of the most common chemistry worksheet, the Periodic Law, the "elements in order" aspect of the Law had been still unresolved - until now. The Alexander Arrangement of Elements format has finally depicted the Periodic Law in an accurate and complete way, halting criticism of the Periodic Table for failing to do so.

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last update 5/18/18