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Periodic table of the elements.

Newlands had tried to set up a table of elements that would allow them to be grouped into natural families (see 1863). A Russian chemist, Dmitry Ivanovich Mendeleyev (1834-1907), now tried his hand at the task.

[TABULAR DATA OMITTED] Like Newlands, Mendeleyev arranged the elements in order of increasing atomic weight. However, he did not try to be too simple and arrange them in a fixed gridwork of seven elements per row. Instead, letting himself be guided by the valence of each element, he allowed the length of the period (row) to increase. He had hydrogen all by itself, then two periods of seven elements each, then two periods of seventeen elements each. He had prepared what is now called the periodic table of the elements.

He published his table on March 6, 1869, beating out others who were attempting the same task, notably the German chemist Julius Lothar Meyer (1830-1895).

In 1871 Mendeleyev went a step further, one which put him in a class by himself. In order to keep the valences and other properties of elements similar as one looked down the columns of his table, he had to leave empty spaces. He did not view this as an imperfection in his table. He merely announced that the empty spaces represented elements that had not yet been discovered.

He picked out three gaps in particular, one under boron, one under aluminum, and one under silicon, and called them eka-boron, eka-aluminum, and eka-silicon. (Eka is "one" in Sanskrit, so that each element is one below the indicated element in the periodic table.) Mendeleyev went on to predict the properties of the missing elements according to their places in the table. Naturally, no one paid this serious attention at the time, but Mendeleyev turned out to be right.

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Author:Asimov, Isaac
Publication:Asimov's Chronology of Science & Discovery, Updated ed.
Article Type:Reference Source
Date:Jan 1, 1994
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