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Tellurium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                52              antimony ← tellurium → iodine
                Se
                ↑
                Te
                ↓
                Po

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                    Name, Symbol, Number tellurium, Te, 52
                                                Chemical series metalloids
                                             Group, Period, Block 16, 5, p
                                          Appearance silvery lustrous gray
                                              Atomic mass 127.60 (3) g/mol
                               Electron configuration [Kr] 4d^10 5s^2 5p^4
                                       Electrons per shell 2, 8, 18, 18, 6
                                                       Physical properties
                                                               Phase solid
                                       Density (near r.t.) 6.24 g·cm^−3
                                    Liquid density at m.p. 5.70 g·cm^−3
                                                   Melting point 722.66  K
                                                (449.51 ° C, 841.12 ° F)
                                                      Boiling point 1261 K
                                                     (988 ° C, 1810 ° F)
                                         Heat of fusion 17.49 kJ·mol^−1
                                   Heat of vaporization 114.1 kJ·mol^−1
                          Heat capacity (25 °C) 25.73 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                         P/Pa  1 10  100   1 k  10 k 100 k
                                        at T/K      (775) (888) 1042 1266

                                                         Atomic properties
                                               Crystal structure hexagonal
                                                Oxidation states ±2, 4, 6
                                                     (mildly acidic oxide)
                                     Electronegativity 2.1 (Pauling scale)
                                                       Ionization energies
                                           ( more) 1st: 869.3 kJ·mol^−1
                                                    2nd: 1790 kJ·mol^−1
                                                    3rd: 2698 kJ·mol^−1
                                                      Atomic radius 140 pm
                                              Atomic radius (calc.) 123 pm
                                                    Covalent radius 135 pm
                                               Van der Waals radius 206 pm
                                                             Miscellaneous
                                             Magnetic ordering nonmagnetic
                                              Thermal conductivity (300 K)
                                           (1.97–3.38) W·m^−1·K^−1
                               Speed of sound (thin rod) (20 °C) 2610 m/s
                                                    Young's modulus 43 GPa
                                                      Shear modulus 16 GPa
                                                       Bulk modulus 65 GPa
                                                        Mohs hardness 2.25
                                                  Brinell hardness 180 MPa
                                            CAS registry number 13494-80-9
                                                         Selected isotopes

                CAPTION: Main article: Isotopes of tellurium

                        iso     NA     half-life     DM   DE ( MeV)   DP
                       ^120Te 0.096%  >2.2×10^16 y ε ε    1.701     ^120Sn
                       ^121Te syn     16.78 d      ε      1.040     ^121Sb
                       ^122Te 2.603%  Te is stable with 70 neutrons
                       ^123Te 0.908%  >1.0×10^13 y ε      0.051     ^123Sb
                       ^124Te 4.816%  Te is stable with 72 neutrons
                       ^125Te 7.139%  Te is stable with 73 neutrons
                       ^126Te 18.952% Te is stable with 74 neutrons
                       ^127Te syn     9.35 h       β^-    0.698     ^127I
                       ^128Te 31.687% 2.2×10^24 y  β^−β^− 0.867     ^128Xe
                       ^129Te syn     69.6 min     β^-    1.498     ^129I
                       ^130Te 33.799% 7.9×10^20 y  β^−β^− 2.528     ^130Xe

                                                                References

   Tellurium ( IPA: /tiˈlʊəriəm, tɛ-/) is a chemical element in the
   periodic table that has the symbol Te and atomic number 52. A brittle
   silver-white metalloid which looks like tin, tellurium is chemically
   related to selenium and sulfur. This element is primarily used in
   alloys and as a semiconductor.

Notable characteristics

   Tellurium crystal
   Enlarge
   Tellurium crystal

   Tellurium is a relatively rare element, in the same chemical family as
   oxygen, sulfur, selenium, and polonium (the chalcogens).

   When crystalline, tellurium is silvery-white and when it is in its pure
   state it has a metallic luster. This is a brittle and easily pulverized
   metalloid. Amorphous tellurium is found by precipitating it from a
   solution of tellurous or telluric acid (Te(OH)[6]). However, there is
   some debate whether this form is really amorphous or made of minute
   crystals. Tellurium is a p-type semiconductor that shows a greater
   conductivity in certain directions which depends on atomic alignment.

   Chemically related to selenium and sulfur, the conductivity of this
   element increases slightly when exposed to light. It can be doped with
   copper, gold, silver, tin, or other metals. Tellurium gives a
   greenish-blue flame when burned in normal air and forms tellurium
   dioxide as a result. When in its molten state, tellurium is corrosive
   to copper, iron, and stainless steel.

Applications

   It is mostly used in alloys with other metals. It is added to lead to
   improve its strength, durability and to decrease the corrosive action
   of sulfuric acid. When added to stainless steel and copper it makes
   these metals more workable. Other uses:
     * It is alloyed into cast iron for chill control.
     * Used in ceramics.
     * It is used in chalcogenide glasses.
     * Bismuth telluride (Bi[2]Te[3]) has found use in thermoelectric
       devices.

   Tellurium is also used in blasting caps, and has potential applications
   in cadmium telluride (CdTe) solar panels. Some of the highest
   efficiencies for solar cell electric power generation have been
   obtained by using this material, but this application has not yet
   caused demand to increase significantly. If some of the cadmium in CdTe
   is replaced by zinc then CdZnTe is formed which is used in solid-state
   x-ray detectors.

   Alloyed with both cadmium and mercury, to form mercury cadmium
   telluride, an infrared sensitive semiconductor material is formed.
   Organotellurium compounds such as dimethyl telluride, diethyl
   telluride, diisopropyl telluride, diallyl telluride and methyl allyl
   telluride are used as precursors for MOVPE growth of II-VI compound
   semiconductors. Diisopropyl telluride (DIPTe) is employed as the
   preferred precursor for achieving the low temperature growth of CdHgTe
   by MOVPE. High purity metalorganics of both selenium and tellurium are
   reported to be obtained by using innovative chemical purification
   strategy, also called adduct purification.

   Organic tellurides have also been employed as initiators for living
   radical polymerisation and electron-rich mono- and di-tellurides
   possess antioxidant activity.

History

   Tellurium (Latin tellus meaning "earth") was discovered in 1782 by the
   Romanian Franz-Joseph Müller von Reichenstein (Müller Ferenc) in Sibiu,
   Romania. In 1789, another Hungarian scientist, Pál Kitaibel, also
   discovered the element independently, but later he gave the credit to
   Müller. In 1798, it was named by Martin Heinrich Klaproth who earlier
   isolated it.

   Tellurium was used as a chemical bonder in the making of the outer
   shell of the first atom bomb. The 1960s brought growth in
   thermoelectric applications for tellurium, as well as its use in
   free-machining steel, which became the dominant use.

Occurrence

   Tellurium is sometimes found in its native (elemental) form, but is
   more often found as the tellurides of gold ( calaverite, krennerite,
   petzite, sylvanite, and others). Tellurium compounds are the only
   chemical compounds of gold found in nature, but tellurium itself
   (unlike gold) is also found combined with other elements (in metallic
   salts). The principal source of tellurium is from anode sludges
   produced during the electrolytic refining of blister copper. It is a
   component of dusts from blast furnace refining of lead. Tellurium is
   produced mainly in the US, Canada, Peru, and Japan.

   Commercial-grade tellurium is usually marketed as minus 200-mesh powder
   but is also available as slabs, ingots, sticks, or lumps. The year-end
   price for tellurium in 2000 was US$ 14 per pound.

Compounds

   Tellurium is in the same series as sulfur and selenium and forms
   similar compounds. A compound with metal or hydrogen and similar ions
   is called a telluride. Gold and silver tellurides are considered good
   ores. Compounds with tellurate ions complexes TeO[4]^2- or TeO[6]^6-
   are known as tellurates.

Isotopes

   There are 30 known isotopes of tellurium with atomic masses that range
   from 108 to 137. Naturally found tellurium consists of eight isotopes
   (listed in the table to the right); three of them are observed to be
   radioactive. ^128Te has the longest known half-life, 2.2×10^24 years,
   among all radioactive isotopes. Tellurium is the first element which
   can undergo Alpha Decay, with isotopes ^106Te to ^110Te being able to
   undergo this mode of decay.

Precautions

   Humans exposed to as little as 0.01 mg/m^3 or less in air develop
   "tellurium breath", which has a garlic-like odor. The garlic odour that
   is associated with human intake of tellurium compounds is caused from
   the tellurium being metabolized by the body. When the body metabolizes
   tellurium in any oxidation state, the tellurium gets converted into
   dimethyl telluride. Dimethyl telluride is volatile and produces the
   garlic-like smell.

   Tellurium and tellurium compounds should be considered to be toxic and
   need to be handled with care.
   Retrieved from " http://en.wikipedia.org/wiki/Tellurium"
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