Thallium

From Wikipedia, the free encyclopedia

81 mercury ← thallium → lead In ↑ Tl ↓ Uut Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	thallium, Tl, 81
Element category	poor metals
Group, Period, Block	13, 6, p
Appearance	silvery white
Standard atomic weight	204.3833(2)  g·mol−1
Electron configuration	[Xe] 4f14 5d10 6s2 6p1
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
Specific heat capacity	(25 °C) 26.32  J·mol−1·K−1
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 µ Ω·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
Most-stable isotopes
Main article: Isotopes of thallium iso NA half-life DM DE (MeV) DP 203Tl 29.524% 203Tl is stable with 122 neutrons 204Tl syn 119 Ms (3.78 y) β- 0.764 204Pb ε 0.347 204Hg 205Tl 70.476% 205Tl is stable with 124 neutrons
References

Thallium (pronounced /ˈθæliəm/) is a chemical element with the symbol Tl and atomic number 81. This soft gray malleable poor metal resembles tin but discolors when exposed to air. Approximately 60-70% of thallium production is used in the electronics industry, and the rest is used in the pharmaceutical industry and in glass manufacturing. It is also used in infrared detectors. Thallium is highly toxic and is used in rat poisons and insecticides, and its use has been cut back or eliminated in many countries. It is used in murders and has the nicknames "The Poisoner's Poison" and "Inheritance powder" (alongside arsenic).

Characteristics

Thallium is very soft and malleable and can be cut with a knife. It has a metallic luster, but when exposed to air, it quickly tarnishes with a bluish-grey 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.

Occurrence and production

Thallium occurs naturally in the minerals crookesite, lorandite, hutchinsonite, and pyrite.

Thallium metal is obtained as a by-product in the production of sulfuric acid by roasting of pyrite, and also in the smelting of lead and zinc ores.

Applications

The odorless and tasteless thallium sulfate was once widely used as rat poison and ant killer. Since 1975, this use in the United States and many other countries is prohibited 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(III) salts, as thallium trinitrate or triacetate, are useful reagents in organic synthesis performing different transformations in aromatics, ketones, olefins, among others.
• thallium bromide-iodide crystals have been used as infrared optical materials, because they are harder than other common infrared optics, and because they have transmission at significantly longer wavelengths. The trade name KRS-5 refers to this material.
• thallium oxide has been used to manufacture glasses that have a high index of refraction.
• used in semiconductor materials for selenium rectifiers,
• used as a dopant for sodium iodide crystals in gamma radiation detection equipment, such as scintillation counters,
• 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 therapeutic index.
• 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 A(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 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.
• an 8.5% thallium amalgam is used in thermometers and switches for use in low temperatures, because it freezes at -58 °C (pure mercury freezes at -38 °C).
• thallium is used in the electrodes in dissolved oxygen analyzers.
• thallium is a constituent of the alloy in the anode plates in magnesium seawater batteries.

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 TlCu₇Se₄, hutchinsonite TlPbAs₅S₉, and lorandite TlAsS₂. It also occurs as trace in pyrite and extracted as a by-product of roasting this ore for sulfuric acid production. The metal can be obtained 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

Main article: isotopes of thallium

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.

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

Compounds

Fluorides: TlF, TlF₃
Chlorides: TlCl, TlCl₂, TlCl₃
Bromides: TlBr, Tl₂Br₄
Iodides: TlI, TlI₃
Hydrides: none listed
Oxides: Tl₂O, Tl₂O₃
Sulfides: Tl₂S
Selenides: Tl₂Se
Tellurides: none listed
Nitrides: none listed

Toxicity

Thallium and its compounds are very toxic, and should be handled with great care[1]. Contact with skin is dangerous, and adequate ventilation should be provided when melting this metal[2].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 (as the atomic radius is almost identical). 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 due to the presence of empty d-orbitals), and so this substitution disrupts many cellular processes (for instance, thallium may attack sulfur-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.

Among the distinctive effects of thallium poisoning are loss of hair (which 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

• 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.
• In 1957, Nikolai Khokhlov, a former KGB assassin, was poisoned with thallium. Khokhlov fell ill with stomach cramps and nausea and within days his hair had fallen out and he was covered with marks on his skin. He fled the Soviet Union to Germany where doctors suspected thallium poisoning and tried every known antidote without success. Khokhlov was then taken to the US hospital and treated with hydrocortisone, steroids, and blood and plasma transfusions and he eventually recovered.
• In 1971, thallium was the main poison that Graham Frederick Young used to poison around 70 people in the English village of Bovingdon, Hertfordshire, of which 2 died.^{[citation needed]}
• Zhu Ling (1973) the victim of an unsolved 1995 thallium poisoning case in Beijing, China. In 1994, Zhu Ling was a sophomore in Class Wuhua2 (Physical Chemistry) at Tsinghua University in Beijing. She began to show strange and debilitating symptoms at the end of 1994, when she reported experiencing acute stomach pain, along with extensive hair loss. Ultimately she was diagnosed on Usenet with poisoning by thallium. To this date speculation of the true poisoner is still discussed by many Chinese expatriates overseas
• In 1988, members of the Carr family from Alturas, Polk County, Florida fell ill from what appeared to be thallium poisoning. Peggy Carr, the mother, died slowly and painfully from the poison. Her son and stepson were critically ill but eventually recovered. The Carr's neighbor, George J. Trepal, a chemist and member of Mensa, was convicted of murdering Mrs. Carr and attempting to murder her family and sentenced to death. The thallium was slipped into bottles of Coca-Cola at the Carr's home and Trepal's.

• 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.
• In February 2007, two Americans, Marina and Yana Kovalevsky, a mother and daughter, visiting Russia were hospitalized due to thallium poisoning. Both had emigrated from the Soviet Union to the United States in 1989 and had made several trips to Russia since then.
• In February 2008, members of Iraqi air force club and some of their children were poisoned by cake laced with thallium. Two of the children died.

In fiction

• 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. This novel is notable as being credited with having saved at least two lives after readers recognised the symptoms of thallium poisoning that Christie described.

• In Nigel Williams' 1990 novel The Wimbledon Poisoner, Henry Far uses thallium to baste a roast chicken in a failed attempt to murder his wife.

• Thallium figures prominently in the 1995 film The Young Poisoner's Handbook, a dark comedy loosely based on the life of Graham Frederick Young.

• "Concentrated thallium" is used as the poison of choice of the Wyoming Widow in the 2006 comedy Big Nothing