Discovery of Element Thorium

Thorium Discovery

In 1815 J. Berzelius, the discoverer of the element, named it thorium in honour of Thor, the ancient Scandinavian god of thunder. But the famous Swedish chemist anticipated the events: no new element was discovered by him that year. He analysed a rare mineral from Falun mines in which he discovered what he  believed to be the oxide of an unknown element. Berzelius thought this justified the addition of one more name to the list of the existing elements. No contemporary dared even to doubt the discovery since in those times the scientists had boundless trust in Berzelius. However, Berzelius himself had doubt, and justifiably so: ten years later it was shown that the oxide observed by him was yttrium phosphate (yttrium had already been known for a long time). Thus, in 1825 the past triumph turned sour.

A year later F. Wohler reported the discovery of a new element in a rare Norwegian mineral now known under the name of “pyrochlore”. Wohler did not attach particular importance to this observation and, as it turned out, mistakenly so.

Meanwhile, G. Esmark found a heavy black mineral on the Leven island near the shores of Norway. The scientist sent a sample of the mineral to J. Berzelius who thoroughly analysed it. In 1828 Berzelius reported isolation of silicates of a new element from the mineral. The old name “thorium” proved useful. The mineral which had become the source of thorium–2 was named by J. Berzelius “thorite”.

When Berzelius studied the properties of thorium, Wohler paid attention to the fact they were similar to those of the element which he left without attention in 1826. Wohler was much more disappointed when six years later the famous German scientist and traveller W. Humboldt presented him with a sample of pyrochlore from Siberia. Wohler discovered thorium in it as a few years earlier he had found it in the Norwegian pyrochlore. Thus, thorium played a trick on Wohler.

  1. Berzelius tried to separate pure thorium but in vain. For very long the element was known in the form of its oxide and only in the 1870’s was it prepared in the metallic form. Thus, thorium became the second radioactive element (after uranium) to be discovered by the conventional chemical analysis having nothing to do with radioactivity.
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