Tellurium

Tellurium,  ₅₂Te

Metallic tellurium, diameter 3.5 cm
General properties
Name, symbol	Tellurium, Te
Appearance	silvery lustrous gray (crystalline), brown-black powder (amorphous)
Tellurium in the periodic table
Se ↑ Te ↓ Po Antimony ← Tellurium → Iodine
Atomic number	52
Standard atomic weight (Ar)	127.6
Group, block	, p-block
Period	period 4
Electron configuration	[Kr] 4d10 5s2 5p4
per shell	2, 8, 18, 18, 6
Physical properties
silvery-gray
Phase	solid
Melting point	722.66 K ​(449.51 °C, ​​841.12 °F)
Boiling point	1261 K ​(988 °C, ​1810 °F)
Density near r.t.	6.24 g/cm3
when liquid, at	5.70 g/cm3
Heat of fusion	17.49 kJ/mol
Heat of	114.1 kJ/mol
Molar heat capacity	25.73 J/(mol·K)
pressure
Atomic properties
Oxidation states	6, 5, 4, 3, 2, 1, −1, −2 ​a mildly acidic oxide
Electronegativity	Pauling scale: 2.1
energies	1st: 869.3 kJ/mol 2nd: 1790 kJ/mol 3rd: 2698 kJ/mol
Atomic radius	empirical: 140 pm
Covalent radius	138±4 pm
Van der Waals radius	206 pm
Miscellanea
Crystal structure	​
Speed of sound thin rod	2610 m/s (at 20 °C)
Thermal expansion	18 µm/(m·K)
Thermal conductivity	1.97–3.38 W/(m·K)
Magnetic ordering	diamagnetic
Young's modulus	43 GPa
Shear modulus	16 GPa
Bulk modulus	65 GPa
Mohs hardness	2.25
Brinell hardness	180–270 MPa
CAS Registry Number	13494-80-9
History
Naming	after Roman Tellus, deity of the Earth
Discovery	Franz-Joseph Müller von Reichenstein (1782)
First isolation	Martin Heinrich Klaproth

Tellurium is the element with symbol Te and atomic number 52.

Properties

Chemical

It is usually found in -2, +2, +4 and +6 oxidation states. It has chemical properties similar to selenium, being dissolved by sulphuric and nitric acid and potassium hydroxide solutions but not in water. It corrodes copper, iron and stainless steel when it's molten. It reacts with oxygen in air, hydrogen and with halogens. It burns with a blueish grey flame. Although being mildly toxic, it is infamous for making you smell really bad so don´t handle it without correct safety equipment.

Physical

Tellurium is a whitish-silvery solid, crystalline element which has a nice, metallic luster. It's a brittle and easily powderized metalloid. It's a good semiconductor, and conductivity increases slightly when exposed to light. It melts at 450 ºC and boils at almost 1000 ºC.

Availability

Tellurium is one of the rarest stable elements on Earth's crust. Applications are scarce, most commonly used in electronics and solar panels. Prices are high and it has few uses for home chemists, in addition to collecting elements.

Rewritable disks contain a small layer of tellurium oxide, though you will need dozens if not hundreds to isolate a significant amount of elemental tellurium.

Tellurium is sometimes found in its native (i.e., elemental) form, but is more often found as the tellurides of gold such as calaverite and krennerite (two different polymorphs of AuTe₂), petzite, Ag₃AuTe₂, and sylvanite, AgAuTe₄.

Production

Tellurium can be prepared by reducing tellurium compounds, like metal tellurides. The procedure is very hazardous, as hydrogen telluride may form during the process. Purchasing the free element may be cheaper.

Gold, silver, copper tellurides are roasted with sodium carbonate under air at temperatures of 500 °C. The metal ions are reduced to the metals, while the telluride is converted to sodium tellurite.

M₂Te + O₂ + Na₂CO₃ → Na₂TeO₃ + 2 M + CO₂

Tellurites can be leached from the mixture with water and are normally present as hydrotellurites HTeO₃⁻ in solution. Selenites may also be formed during this process if any selenides are present, but they can be separated by adding sulfuric acid. The hydrotellurites are converted into the insoluble tellurium dioxide, while the selenites stay in solution.

HTeO−
3 + OH⁻ + H₂SO₄ → TeO₂ + SO2−
4 + 2 H₂O

Elemental tellurium is obtained by reducing the oxide either by electrolysis or by reacting the tellurium dioxide with sulfur dioxide in sulfuric acid.

TeO₂ + 2 SO₂ + 2H₂O → Te + 2 SO2−
4 + 4 H⁺

The above procedure may not work on other tellurides, like cadmium telluride.

Projects

• Make tellurium dioxide
• Make sodium tellurite

Handling

Safety

Wear appropriate protection when handling it or it's compounds. Certain compounds such as cadmium telluride are highly toxic.

When small amounts are ingested, tellurium and its compounds are metabolized to dimethyl telluride, causing a foul garlic-like odor named "tellurium breath".

Storage

Tellurium should be stored in closed containers.

Disposal

It is best to try to recycle it.

References

Relevant Scencemadness threads

• Tellurium
• tellurium at a good price
• quite the silly question: Tellerium