Introduction history, abundance, distribution

Tellurium was the first of these three elements to be discovered. It was isolated by the Austrian chemist F. J. Muller von Reichenstein in 1782 a few years after the discovery of oxygen by J. Priestley and C. W. Scheele (p. 600), though the periodic group relationship between the elements was not apparent until nearly a century later (p. 20). Tellurium was first 

Selenium was isolated some 35 y after tellurium and, since the new element resembled tellurium, it was named from the Greek askrivr], selene, the moon. The discovery was made in 1817 by the Swedish chemist J. J. Berzelius (discoverer of Si, Ce and Th) and J. G. Gahn (discoverer of Mn) they observed a reddish-brown deposit during the burning of sulfur obtained from Fahlun copper pyrites, and showed it to be volatile and readily reducible to the new element. 

The discovery of polonium by Marie Curie in 1898 is a story that has been told many 

Polonium has no stable isotopes, all 27 isotopes being radioactive of these only °Po occurs naturally, as the penultimate member of the radium decay series  

Because of the fugitive nature of °Po, uranium ores contain only about 0.1 mg Po per tonne of ore (i.e. 10 ppm). The overall abundance of Po in crustal rocks of the earth is thus of the order of 3 X 10- 0 ppm. 

Marie Curie, in E. Farber (ed.). Great Chemists, pp. 1263-75. Interscience, New York, 1961. 

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