Introduction to Tellurium
Tellurium, symbolized as Te, is a brittle, silvery-white metalloid element with an atomic number of 52. It is situated in Group 16 of the periodic table, alongside oxygen, sulfur, and selenium, and is thus classified as a chalcogen. Tellurium is a relatively rare element, found in the Earth’s crust at an abundance comparable to gold. Its properties often bridge those of metals and nonmetals.
Chemical Reactivity
The chemical reactivity of tellurium is influenced by its position in the periodic table. It exhibits characteristics of both metallic and nonmetallic elements.
Reaction with Water
Tellurium generally shows very low reactivity with water. At standard temperatures and pressures, elemental tellurium does not react with water. Under extremely high temperatures, such as when exposed to steam, a reaction may occur, but this is not typical under normal environmental conditions.
Reaction with Air
Tellurium is stable in air at room temperature and does not readily oxidize. However, when heated in air or oxygen, tellurium burns with a distinctive blue-green flame. This combustion reaction forms tellurium dioxide (TeO2), a white, crystalline solid.
Te(s) + O₂(g) → TeO₂(s)
This behavior aligns with its group members, where heavier chalcogens require heating to react with oxygen.
General Chemical Behavior
Tellurium exhibits various oxidation states, most commonly -2, +2, +4, and +6. It readily forms compounds with halogens, such as tellurium tetrafluoride (TeF4) and tellurium tetrachloride (TeCl4). It also forms tellurides with many metals, which are compounds where tellurium is in the -2 oxidation state, similar to how oxygen forms oxides or sulfur forms sulfides.
Safety and Physical Properties
Understanding tellurium’s safety and physical properties is crucial for its handling and application.
Toxicity
Tellurium and many of its compounds are considered toxic. Exposure can occur through inhalation, ingestion, or skin contact. A characteristic symptom of tellurium exposure, even at very low levels, is a strong garlic-like odor on the breath and body, often referred to as “tellurium breath.” This odor is caused by the body’s metabolism of tellurium into volatile dimethyl telluride ((CH3)2Te). High levels of exposure can lead to more severe health effects, including nervous system disorders, kidney damage, and liver dysfunction. Therefore, careful handling and appropriate safety measures are necessary when working with tellurium and its compounds.
Radioactivity
Tellurium is not generally classified as a radioactive element that poses a significant hazard. While it has several naturally occurring isotopes, including eight stable ones, some isotopes exhibit extremely long half-lives for processes like double beta decay (e.g., Tellurium-128 with a half-life estimated to be 2.2 × 10^24 years). This decay rate is so slow that it does not contribute to practical radioactivity concerns or applications. Tellurium is not used in radioactive sources or nuclear applications.
Flammability
Elemental tellurium is not considered flammable under normal atmospheric conditions or at room temperature. As noted previously, it will burn when heated to elevated temperatures in the presence of air or oxygen, producing tellurium dioxide. This is a combustion reaction rather than an inherent flammability at ambient conditions.
Notable Chemical Reaction Example
One of the most notable chemical reactions involving tellurium occurs naturally in geological processes: the formation of gold tellurides. Gold, typically known for its inertness and reluctance to form chemical compounds, readily combines with tellurium to form stable minerals. Examples include calaverite (AuTe2) and sylvanite ((Au,Ag)Te2). These gold telluride ores are significant sources of gold in various mining regions globally, such as Kalgoorlie in Western Australia and Cripple Creek in Colorado, USA. The chemical reaction between gold and tellurium in these geological formations demonstrates tellurium’s unique ability to bond with an otherwise unreactive noble metal. This reactivity is critical for the processes used to extract gold from these specific ore types.