Thorium

Misclassification

Thorium, located in the 90th place on the periodic table, has unique properties that make it useful in certain applications. The story of thorium begins in 1815 at the Falun copper mine in Sweden, where a previously unknown mineral was discovered and given to chemist Johns Jacob Berzelius to analyze. Berzelius, who had previously discovered cerium and selenium, mistakenly identified the mineral as a new element and named it thorium after the Norse god of thunder 1. However, it was later found to be yttrium orthophosphate.

The story of thorium begins in 1815 at the Falun copper mine in Sweden. Falun at the time was the most productive copper mine in the world, and copper from the mine had been the single biggest export from Sweden over the previous several centuries.

--- Gary Arndt

In 1828, amateur Norwegian mineralogist Morten Thron Esmark discovered an unusual mineral in Telemark, Norway, which was eventually sent to Berzelius for further analysis 1.

   

Confirmation

Upon re-analysis, Berzelius confirmed that the mineral was indeed a new element, which he named thorium. This time, he got it right, and the mineral was dubbed thorite 2. For decades, thorium had no practical use until it was used in gas lamp mantles in 1885. These mantles, made of thorium oxide, glowed brightly when heated with a gas flame.

Both the German chemist Gerhard Karl Schmidt and the Polish-born Marie Curie discovered that thorium was radioactive. This was the second element which was discovered to have this property after uranium, which was discovered two years earlier.

--- Gary Arndt

In 1898, thorium's radioactivity was discovered by Gerhard Karl Schmidt and Marie Curie, making it the second element known to be radioactive after uranium 2.