Tellurium (Te)

Stable isotopes of tellurium available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Chemical Form
Te-120  52  68  119.904048 0.09%  99.90% Metal
Te-120 52 68 119.904048 0.09% 99.40-99.90% Oxide
Te-122 52 70 121.903056 2.55% 99.90% Metal
Te-122 52 70 121.903056 2.55% 99.90% Oxide
Te-123 52 71 122.904271 0.89% 99.90% Metal
Te-123 52 71 122.904271 0.89% 99.90% Oxide
Te-124 52 72 123.902819 4.74% 99.90% Metal
Te-124 52 72 123.902819 4.74% 99.90% Oxide
Te-125 52 73 124.904424 7.07% 99.00-99.90% Metal
Te-125 52 73 124.904424 7.07% 99.00-99.90% Oxide
Te-126 52 74 125.903305 18.84% 96.60-99.90% Metal
Te-126 52 74 125.903305 18.84% 96.60-99.90% Oxide
Te-128 52 76 127.904462 31.74% 99.90% Metal
Te-128 52 76 127.904462 31.74% 98.80-99.90% Oxide
Te-130  52  78  129.906229 34.08%  ≥99.70% Metal
Te-130 52 78 129.906229 34.08% ≥99.70% Oxide

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Tellurium was discovered in 1783 by Franz-Joseph Müller Freiherr von Reichenstein, an Austrian mineralogist and mining engineer. Its name originates with the Latin word tellus, meaning “earth.”

Tellurium is a silvery white, lustrous solid. It is soluble in sulfuric acid, nitric acid, potassium hydroxide, potassium cyanide solution, caustic potash, and solutions of alkali metal cyanides. It is insoluble in water, carbon disulfide, benzene and hydrochloric acid. It burns in air with a greenish-blue flame; the combustion product is dioxide, the most stable oxide of the metal. Tellurium also forms other oxides: monoxide, trioxide and pentoxide. It combines with halogens, forming halides at different oxidation states. It also forms a black dichloride and a brown dibromide, usually by its reaction with dichlorodifluoromethane and trifluorobromomethane. It forms binary tellurides with several metals: the reaction is carried out by heating tellurium with a metal in stoichiometric amounts in the absence of air in an evacuated ampoule. Tellurium reacts with halides of several metals, when heated in a stream of hydrogen, to produce metal tellurides.

Small amounts of tellurium are added to stainless steel and copper to improve their machinability. It enhances the strength and hardness of lead and protects lead from the corrosive action of sulfuric acid. Tellurium also is a strong chilling agent in iron castings: it controls the chill and imparts a tough abrasion resistance to the surface. Tellurium is a curing agent for natural and synthetic rubber: it improves mechanical properties of the rubber, imparting resistance to heat and abrasion. It is a coloring agent in glass, ceramics and enamels. Traces of tellurium incorporated into platinum catalysts make the catalytic hydrogenation of nitric oxide favorable to the formation of hydroxylamine. A major application of tellurium is in semiconductor research. Tellurides of lead and bismuth are used in thermoelectric devices for power generation and refrigeration.

Human exposure to tellurium causes “garlic breath” due to dimethyl telluride, which persists for a considerable period after exposure. The toxic effects of tellurium are nausea, giddiness, headache, metallic taste, and dryness in the throat.

Properties of Tellurium

Name Tellurium 
Symbol Te 
Atomic number 52 
Atomic weight 127.60 
Standard state Solid at 298 °K 
CAS Registry ID 13494-80-9 
Group in periodic table 16 
Group name Chalcogen 
Period in periodic table
Block in periodic table p-block 
Color Silvery lustrous gray 
Classification Semi-metallic 
Melting point 452 °C
Boiling point 989.8 °C
Vaporization point 990 ºC
Thermal conductivity (1.97–3.38) W/(m·K)
Electrical resistivity 4.36 x 105 µΩ·cm at 25 °C 
Electronegativity 2.1 
Heat of vaporization 48 kJ·mol-1
Heat of fusion 17.5 kJ·mol-1
Density of liquid 5.70 g/cm3 at 452 °C 
Density of solid 6.24 g/cm
Mohs hardness scale 2.3
Electron configuration [Kr]4d105s25p4
Atomic radius 1.42 Å 
Ionic radii Te+4: 0.97 Å and Te+6: 0.5 6Å (coordination number 6)
Oxidation states  +2, +4, +6 

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