Tellurium

Tellurium is a brittle, silver-white metalloid in group 16, below selenium and above polonium. With the configuration [Kr] 4d10 5s2 5p4, it can gain two electrons to form telluride ions (−2), as in cadmium telluride, or use its valence electrons in the +4 and +6 states, as in tellurium dioxide and telluric acid. Crystalline tellurium consists of spiral chains of atoms, like selenium, and it is a semiconductor whose conductivity rises slightly when light falls on it. Down group 16, metallic character increases, and tellurium sits close to the line between metals and non-metals.

Tellurium is one of the rarest stable elements in Earth's crust, roughly as scarce as platinum. During the planet's formation it probably combined with hydrogen to form volatile hydrogen telluride, which escaped into space. Most tellurium is recovered from the anode slimes of copper refineries. Its largest use is in cadmium telluride solar panels, whose thin films absorb sunlight more strongly than silicon. Bismuth telluride is the standard material for thermoelectric coolers, which pump heat when a current flows, and germanium-antimony-tellurium alloys store data in rewritable optical discs by switching between crystalline and glassy states.

Discovery

In 1782 Franz-Joseph Müller von Reichenstein, an Austrian mining inspector in Transylvania, examined a gold ore from Zlatna that yielded a metal-like substance he could not identify. He sent a sample to Martin Heinrich Klaproth in Berlin, who confirmed in 1798 that it was a new element. Klaproth named it tellurium, from the Latin tellus, meaning 'earth', fittingly for an element later paired with selenium, named after the Moon.