thallium

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	diamagnetic[1]
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.^[2] It is also used in infrared detectors. Thallium is highly toxic and is used in rat poisons and insecticides, but its use has been cut back or eliminated in many countries. Because of its use for murder, thallium has gained the nicknames "The Poisoner's Poison" and "Inheritance Powder" (alongside arsenic).

Characteristics

1 gram of Thallium

Thallium is very soft and malleable and can be cut with a knife at room temperature. 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.

History

Thallium (Greek θαλλός, thallos, meaning "a green shoot or twig")^[3] was discovered by flame spectroscopy in 1862. The name comes from thallium's bright green spectral emission lines.

After the publication of the improved method of flame spectroscopy by Robert Bunsen and Gustav Kirchhoff^[4] and the discovery of caesium and rubidium in the years 1859 to 1860 flame spectroscopy became an approved method to determine the composition of minerals and chemical products. William Crookes and Claude-Auguste Lamy both started to use the new method. William Crookes used it to make spectroscopic determinations for tellurium on selenium compounds deposited in the lead chamber of a sulfuric acid production plant near Tilkerode in the Harz mountains. He had obtained the samples for his research on selenium cyanide from August Hofmann years earlier.^[5][6] By 1862 Crookes was able to isolate small quantities of the element and determine the properties of a few compounds.^[7] Claude-Auguste Lamy used a similar spectrometer to Crookes' to determine the composition of a selenium-containing substance which deposited during the production of sulfuric acid from pyrite. He also noticed the new green line in the spectra and concluded that a new element was present. Lamy had received this material from the sulfuric acid plant of his friend Fréd Kuhlmann and this byproduct was available in large quantities. Lamy started to isolate the new element from that source.^[8] The fact that Lamy was able to work ample quantities of thallium enabled him to determine the properties of several compounds and in addition he prepared a small ingot of metallic thallium which he prepared by remelting thallium he had obtained by electrolysis of thallium salts.

As both scientists discovered thallium independently and a large part of the work, especially the isolation of the metallic thallium was done by Lamy, Crookes tried to secure his priority on the work. Lamy was awarded a medal at the International Exhibition in London 1862: For the discovery of a new and abundant source of thallium and after heavy protest Crookes also received medal: thallium, for the discovery of the new element. The controversy between both scientists continued through 1862 and 1863. Most of the discussion ended after Crookes was elected Fellow of the Royal Society in June 1863.^[9][10]

Occurrence and production

Corroded thallium rod

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.^[2] 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. Thallium metal can also be obtained as a by-product in the production of sulfuric acid by roasting of pyrite.^[2][11]

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.

²⁰²Tl (half life 12.23 days) can be made in a cyclotron,^[12] while ²⁰⁴Tl (half life 3.78 years) is made by the neutron activation of stable thallium in a nuclear reactor.^[13]

Compounds

Fluorides: Thallium(I) fluoride (TlF), Thallium(III) fluoride (TlF₃)
Chlorides: Thallium(I) chloride (TlCl), Thallium(II) chloride (TlCl₂), Thallium(III) chloride (TlCl₃)
Bromides: Thallium(I) bromide (TlBr), Thallium(II) bromide (Tl₂Br₄)
Iodides: Thallium triiodide (TlI), Thallium triiodide (TlI₃)
Hydrides: none listed
Oxides: Thallium oxide (Tl₂O), Thallium(III) oxide (Tl₂O₃)
Sulfides: Thallium(I) sulfide Tl₂S
Selenides: Thallium(I) selenide Tl₂Se
Tellurides: none listed
Nitrides: none listed

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.^[2] Other uses:

• thallium(I) sulfide's electrical conductivity changes with exposure to infrared light therefore making this compound useful in photocells.^[14][15]
• thallium(III) salts, as thallium trinitrate or triacetate, are useful reagents in organic synthesis performing different transformations in aromatics, ketones, olefins, among others.
• Thallium(I) bromide and thallium(I) 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.^[14]
• used in semiconductor materials for selenium rectifiers,^[14]
• 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.^[14]
• 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).^[16][17] This isotope of thallium can be generated using a transportable generator which is similar to the technetium cow.^[18] 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.^[19]
• Thallium oxide has been used to manufacture glasses that have a high index of refraction. 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.^[14]
• A mercury-thallium alloy, which forms a eutectic at 8.5% thallium, is reported to freeze at –60 °C,

some 20 °C below the freezing point of mercury. This allow is used in thermometers and low-temperature switches.^[14]

• thallium is used in the electrodes in dissolved oxygen analyzers.^[2]
• thallium is a constituent of the alloy in the anode plates in magnesium seawater batteries.^[2]

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. After the discovery of the first thallium barium calcium copper oxide superconductor in 1988 the research in applications started.^[20]

Toxicity

Thallium and its compounds are extremely 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.^[21].

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. Up to 20 g per day of Prussian blue is fed by mouth to the person, and it passes through their digestive system and comes out in the stool. Hemodialysis and hemoperfusion are also used to remove thallium from the blood serum. At later stage of the treatment additional potassium is used to mobilize thallium from the tissue.^[22][23]

Bioconcentration

According to the United States Environmental Protection Agency (EPA), thallium release to the environment was reported in Texas and Ohio. This may indicate bioconcentration in aquatic ecosystems.^[24]

See also

• Thallium poisoning
• Thallium compounds

References

External links

Wikimedia Commons has media related to: Thallium

Look up thallium in Wiktionary, the free dictionary.

• WebElements.com — Thallium
• pure Thallium >=99,99% picture in the element collection from Heinrich Pniok
• Toxicity, Thallium
• NLM Hazardous Substances Databank – Thallium, Elemental
• ATSDR - ToxFAQs*pure Thallium cast in acrylic for safe handling