Tellurium (Te), atomic number 52, is a relatively rare element within the Earth’s crust, occurring at an abundance comparable to platinum. This silvery-white element is primarily recovered as a byproduct of copper and lead refining. Its unique physical and chemical characteristics place it in an ambiguous position on the Periodic Table, which frequently leads to confusion regarding its precise classification among metals and nonmetals.
Tellurium’s Official Classification
Tellurium is formally classified as a metalloid, often referred to as a semi-metal, because it exhibits properties of both metals and nonmetals. This designation is based on its position along the “staircase” line of the Periodic Table, which separates metallic elements from nonmetallic ones. Tellurium is located in Group 16, also known as the chalcogen group, and Period 5. Its placement in the p-block indicates its intermediate nature, sharing chemical similarities with nonmetals like sulfur and selenium, while displaying a metallic appearance.
Defining Properties of a Metalloid
The metalloid classification is justified by Tellurium’s conflicting physical characteristics. In its crystalline form, the element possesses a silvery-white luster, giving it a metallic appearance similar to tin or antimony. This metallic sheen is coupled with the ability to form alloys with other metals, such as copper and iron, a behavior typically associated with true metals.
However, Tellurium is also brittle and can be easily pulverized into a powder, unlike metals which are generally malleable and ductile. This mechanical fragility is a property shared with nonmetals like sulfur and phosphorus. Chemically, Tellurium’s reactivity is intermediate, reacting with both metals to form tellurides and nonmetals to form various compounds.
Its electrical conductivity categorizes it as a semiconductor. Tellurium conducts electricity, but not as efficiently as a metal like copper or silver. A defining feature of its semiconductivity is that its electrical resistance decreases as its temperature increases, which is the opposite of how true metals behave. This temperature-dependent conductivity makes Tellurium highly valued in the electronics industry.
Practical Uses in Modern Technology
The semiconducting properties of Tellurium translate directly into several high-technology applications. Its most significant use is in the production of Cadmium Telluride (CdTe) thin-film solar cells, a highly efficient and cost-effective photovoltaic technology. In these devices, the Tellurium compound absorbs sunlight and converts it into electrical energy.
Tellurium is also utilized in thermoelectric devices, where compounds such as Bismuth Telluride convert temperature differences into electrical energy and vice versa. This allows for power generation from waste heat and solid-state cooling applications. Additionally, the element is used in metallurgy to create specialized free-machining alloys.
Adding a small amount of Tellurium to steel or copper significantly improves the metal’s machinability, allowing for higher cutting speeds and better surface finishes. Compounds of Tellurium are also used as a component in rewritable optical discs, such as CD-RWs and DVD-RWs. The element’s ability to change its reflective properties when heated and cooled is exploited to store and retrieve data.