“The periodic table is arguably the most important concept in chemistry.' Happy periodictableday! (From 2019)
Other chemists perceived links between atomic weights and chemical properties, but it was not until the 1860s that atomic weights had been well enough understood and measured for deeper insights to emerge. In England, the chemist John Newlands noticed that arranging the known elements in order of increasing atomic weight produced a recurrence of chemical properties every eighth element, a pattern he called the “law of octaves” in an 1865 paper.
By early 1869, Mendeleev had made enough progress to realize that some groups of similar elements showed a regular increase in atomic weights; other elements with roughly equal atomic weights shared common properties. It appeared that ordering the elements by their atomic weight was the key to categorizing them.
Not only had Mendeleev predicted the existence of these elements, but he had also correctly described their properties in detail. Gallium, for instance, discovered in 1875, had an atomic weight of 69.9 and a density six times that of water. Mendeleev had predicted an element with just that density and an atomic weight of 68. His predictions for eka-silicon closely matched germanium in atomic weight and density .
In his textbook, Mendeleev had noted that “internal differences of the matter that comprises the atoms” could be responsible for the elements’ periodically recurring properties. But he did not pursue that line of thought. In fact, over the years he waffled about how important atomic theory was for his table.
France Dernières Nouvelles, France Actualités
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