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Thallium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


               81                 mercury ← thallium → lead
               In
               ↑
               Tl
               ↓
               Uut

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                     Name, Symbol, Number thallium, Tl, 81
                                               Chemical series poor metals
                                             Group, Period, Block 13, 6, p
                                                  Appearance silvery white
                                            Atomic mass 204.3833 (2) g/mol
                         Electron configuration [Xe] 4f^14 5d^10 6s^2 6p^1
                                   Electrons per shell 2, 8, 18, 32, 18, 3
                                                       Physical properties
                                                               Phase solid
                                      Density (near r.t.) 11.85 g·cm^−3
                                   Liquid density at m.p. 11.22 g·cm^−3
                                                      Melting point 577  K
                                                      (304 ° C, 579 ° F)
                                                      Boiling point 1746 K
                                                    (1473 ° C, 2683 ° F)
                                          Heat of fusion 4.14 kJ·mol^−1
                                     Heat of vaporization 165 kJ·mol^−1
                          Heat capacity (25 °C) 26.32 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                        P/Pa   1  10  100  1 k  10 k 100 k
                                       at T/K 882 977 1097 1252 1461 1758

                                                         Atomic properties
                                               Crystal structure hexagonal
                                                     Oxidation states 3, 1
                                                      (mildly basic oxide)
                                    Electronegativity 1.62 (Pauling scale)
                                     Ionization energies 1st: 589.4 kJ/mol
                                                          2nd: 1971 kJ/mol
                                                          3rd: 2878 kJ/mol
                                                      Atomic radius 190 pm
                                              Atomic radius (calc.) 156 pm
                                                    Covalent radius 148 pm
                                               Van der Waals radius 196 pm
                                                             Miscellaneous
                                                    Magnetic ordering  ???
                              Electrical resistivity (20 °C) 0.18 µΩ·m
                       Thermal conductivity (300 K) 46.1 W·m^−1·K^−1
                       Thermal expansion (25 °C) 29.9 µm·m^−1·K^−1
                                Speed of sound (thin rod) (20 °C) 818 m/s
                                                     Young's modulus 8 GPa
                                                     Shear modulus 2.8 GPa
                                                       Bulk modulus 43 GPa
                                                        Poisson ratio 0.45
                                                         Mohs hardness 1.2
                                                 Brinell hardness 26.4 MPa
                                             CAS registry number 7440-28-0
                                                         Selected isotopes

                 CAPTION: Main article: Isotopes of thallium

                              iso     NA    half-life DM  DE ( MeV)   DP
                             ^203Tl 29.524% Tl is stable with 122 neutrons
                             ^204Tl syn     119 Ms
                                            (3.78 y)  β^- 0.764     ^204Pb
                                                      ε   0.347     ^204Hg
                             ^205Tl 70.476% Tl is stable with 124 neutrons

                                                                References

   Thallium ( IPA: /ˈθaliəm/) is a chemical element in the periodic table
   that has the symbol Tl and atomic number 81. This soft gray malleable
   poor metal resembles tin but discolors when exposed to air. Thallium is
   highly toxic and is used in rat poisons and insecticides but since it
   might also cause cancer (although the EPA does not class it as
   carcinogen), this use has been cut back or eliminated in many
   countries. It is also used in infrared detectors. It has even been used
   in some murders, earning the nicknames "The Poisoner's Poison" and
   "Inheritance powder" (alongside arsenic).

Notable characteristics

   1 gram of Thallium
   Enlarge
   1 gram of Thallium

   This metal is very soft and malleable and can be cut with a knife. When
   it is first exposed to air, thallium has a metallic luster but quickly
   tarnishes with a bluish-gray tinge that resembles lead (it is preserved
   by keeping it under oil). A heavy layer of oxide builds up on thallium
   if left in air. In the presence of water, thallium hydroxide is formed.

Applications

   The odorless and tasteless thallium sulfate was widely used in the past
   as a rat poison and ant killer. In the United States and many other
   countries this use is no longer allowed due to safety concerns. Other
   uses:
     * thallium sulfide's electrical conductivity changes with exposure to
       infrared light therefore making this compound useful in photocells.
     * thallium bromide- iodide crystals have been used as infrared
       optical materials.
     * thallium oxide has been used to manufacture glasses that have a
       high index of refraction.
     * used in semiconductor materials for selenium rectifiers,
     * in gamma radiation detection equipment,
     * high-density liquid used for sink-float separation of minerals,
     * used in the treatment of ringworm and other skin infections.
       However this use has been limited due to the narrow margin that
       exists between toxicity and therapeutic benefit.
     * radioactive thallium-201 (half-life of 73 hours) is used for
       diagnostic purposes in nuclear medicine, particularly in stress
       tests used for risk stratification in patients with coronary artery
       disease (CAD). . This isotope of thallium can be generated using a
       transportable generator which is similar to the technetium cow. The
       generator contains lead-201 (half life 9.33 hours) which decays by
       electron capture to the thallium-201. The lead-201 can be produced
       in a cyclotron by the bombardment of thallium with with protons or
       deuterons by the (p,3n) and (d,4n) reactions.

     * combined with sulfur or selenium and arsenic, thallium has been
       used in the production of high- density glasses that have low
       melting points in the range of 125 and 150 °C. These glasses have
       room temperature properties that are similar to ordinary glasses
       and are durable, insoluble in water and have unique refractive
       indices.
     * thallium amalgam is used in thermometers for low temperature,
       because it freezes at -58 °C (pure mercury freezes at -38 °C).

   In addition, research activity with thallium is ongoing to develop
   high-temperature superconducting materials for such applications as
   magnetic resonance imaging, storage of magnetic energy, magnetic
   propulsion, and electric power generation and transmission.

History

   Thallium ( Greek θαλλός, thallos, meaning "a green shoot or twig") was
   discovered by Sir William Crookes in 1861 in England while he was
   making spectroscopic determinations for tellurium on residues from a
   sulfuric acid plant. The name comes from Thallium's bright green
   spectral emission lines. In 1862 Crookes and Claude-Auguste Lamy
   isolated the metal independently of each other.

Occurrence

   Although the metal is reasonably abundant in the Earth's crust at a
   concentration estimated to be about 0.7 mg/kg, mostly in association
   with potassium minerals in clays, soils, and granites, it is not
   generally considered to be commercially recoverable from those forms.
   The major source of commercial thallium is the trace amounts found in
   copper, lead, zinc, and other sulfide ores.

   Thallium is found in the minerals crookesite TlCu[7]Se[4],
   hutchinsonite TlPbAs[5]S[9], and lorandite TlAsS[2]. This metal is also
   contained in pyrites and is extracted as a by-product of sulfuric acid
   production when pyrite ore is roasted. Another way this element is
   obtained is from the smelting of lead and zinc rich ores. Manganese
   nodules found on the ocean floor also contain thallium, but nodule
   extraction is prohibitively expensive and potentially environmentally
   destructive. In addition, several other thallium minerals, containing
   16% to 60% thallium, occur in nature as sulfide or selenide complexes
   with antimony, arsenic, copper, lead, and silver but are rare and have
   no commercial importance as sources of this element. See also:
   Category:Thallium minerals.

Isotopes

   Thallium has 25 isotopes which have atomic masses that range from 184
   to 210. ^203Tl and ^205Tl are the only stable isotopes and ^204Tl is
   the most stable radioisotope with a half-life of 3.78 years.

   Thallium-202 (half life 12.23 days) can be made in a cyclotron while
   thallium-204 (half life 3.78 years) is made by the neutron activation
   of stable thallium in a nuclear reactor.

Toxicity

   Thallium and its compounds are highly toxic and should be handled with
   great care. Contact with skin is dangerous and adequate ventilation
   should be provided when melting this metal. Thallium(I) compounds have
   a high aqueous solubility and are readily absorbed through the skin.
   Exposure to them should not exceed 0.1 mg per m² of skin in an 8-hour
   time-weighted average (40-hour work week). Thallium is a suspected
   human carcinogen.

   Part of the reason for thallium's high toxicity is that, when present
   in aqueous solution as the univalent thallium(I) ion (Tl^+), it
   exhibits some similarities with essential alkali metal cations,
   particularly potassium. It can thus enter the body via potassium uptake
   pathways. However other aspects of thallium's chemistry are very
   different from that of the alkali metals (e.g. its high affinity for
   sulfur ligands), and so this substitution disrupts many cellular
   processes (for instance thallium may attack sulphur-containing proteins
   such as cysteine residues and ferredoxins).

   Thallium's toxicity has led to its use (now discontinued in many
   countries) as a rat and ant poison.

   Amongst the distinctive effects of thallium poisoning are loss of hair
   (which ironically led it to its initial use as a depilatory, before its
   toxicity was properly appreciated), and damage to peripheral nerves
   (victims may experience a sensation of walking on hot coals). Thallium
   was once an effective murder weapon before its effects became
   understood and an antidote ( prussian blue) discovered.

Treatment and internal decontamination

   One of the main methods of removing thallium (both radioactive and
   normal) from humans is to use Prussian blue, which is a solid ion
   exchange material which absorbs thallium and releases potassium. The
   prussian blue is fed by mouth to the person, and it passes through
   their digestive system and comes out in the stool.

Famous uses as a poison

     * Agatha Christie, who worked as a pharmacist, used thallium as the
       agent of murder in her detective fiction novel The Pale Horse — the
       first clue to the murder method coming from the hair loss of the
       victims.

     * The CIA is believed (by its Inspector General) to have conceived a
       scheme to poison Fidel Castro by exposure to thallium salts placed
       in his shoes while they were being polished. The goal was to
       discredit him by causing him to lose his characteristic hair and
       beard. The scheme progressed as far as testing on animals, but the
       trip during which the poison was to be administered fell through.

     * In 1953, Australian Caroline Grills was sentenced to life in prison
       after three family members and a close family friend died.
       Authorities found thallium in tea that she had given to two
       additional family members.

     * Dr. Félix-Roland Moumié, a leader of the Cameroonian anticolonial
       armed struggle against France was murdered by thallium poisoning on
       October 15, 1960. A French agent posing as a journalist was the
       main suspect of this murder.

     * It is claimed that South African agents once plotted to use it
       against Nelson Mandela while he was in prison on Robben Island. The
       Truth and Reconciliation Commission heard how agents established
       plans to add doses of the chemical to his medication.

     * In the 1960s and 1970s, Graham Frederick Young killed at least
       three people with thallium. The 1995 film The Young Poisoner's
       Handbook is based upon him.

     * In 1995, Zhu Ling, a student at Tsinghua University in Beijing,
       China, was reportedly poisoned twice by her roommate, over a period
       of a few months. The classmates of the victim asked for help
       through Usenet, to which access was very new in mainland China at
       the time. Joint efforts by physicians who responded through the web
       led to the diagnosis of thallium poisoning. The case was covered by
       news reports around the world.

   Corroded Thallium rod
   Enlarge
   Corroded Thallium rod
     * In June 2004, 25 Russian soldiers earned Honorable Mention Darwin
       Awards after becoming ill from thallium exposure when they found a
       can of mysterious white powder in a rubbish dump on their base at
       Khabarovsk in the Russian Far East. Oblivious to the danger of
       misusing an unidentified white powder from a military dump site,
       the conscripts added it to tobacco, and used it as a substitute for
       talcum powder on their feet.

     * In 2005, a 17 year old girl in Numazu, Shizuoka, Japan, admitted to
       attempting to murder her mother by lacing her tea with thallium,
       causing a national scandal.

   Retrieved from " http://en.wikipedia.org/wiki/Thallium"
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   with only minor checks and changes (see www.wikipedia.org for details
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