Thallium

Thallium is a chemical element with symbol Tl and atomic number 81. It is a gray post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Chemists William Crookes and Claude-Auguste Lamy discovered thallium independently in 1861, in residues of sulfuric acid production. Both used the newly developed method of flame spectroscopy, in which thallium produces a notable green spectral line. Thallium, from Greek θαλλός, thallós, meaning "a green shoot or twig", was named by Crookes. It was isolated by both Lamy and Crookes in 1862; Lamy by electrolysis, and Crookes by precipitation and melting of the resultant powder. Crookes exhibited it as a powder precipitated by zinc at the International exhibition, which opened on 1 May that year.[5]

Thallium tends to oxidize to the +3 and +1 oxidation states as ionic salts. The +3 state resembles that of the other elements in group 13 (boron, aluminium, gallium, indium). However, the +1 state, which is far more prominent in thallium than the elements above it, recalls the chemistry of alkali metals, and thallium(I) ions are found geologically mostly in potassium-based ores, and (when ingested) are handled in many ways like potassium ions (K+) by ion pumps in living cells.

Commercially, thallium is produced not from potassium ores, but as a byproduct from refining of heavy-metal sulfide ores. Approximately 60–70% of thallium production is used in the electronics industry, and the remainder is used in the pharmaceutical industry and in glass manufacturing.[6] It is also used in infrared detectors. The radioisotope thallium-201 (as the soluble chloride TlCl) is used in small, nontoxic amounts as an agent in a nuclear medicine scan, during one type of nuclear cardiac stress test.

Soluble thallium salts (many of which are nearly tasteless) are toxic, and they were historically used in rat poisons and insecticides. Use of these compounds has been restricted or banned in many countries, because of their nonselective toxicity. Thallium poisoning usually results in hair loss, although this characteristic symptom does not always surface. Because of its historic popularity as a murder weapon, thallium has gained notoriety as "the poisoner's poison" and "inheritance powder" (alongside arsenic).[7]

Thallium,  81Tl
Thallium pieces in ampoule
Thallium
Pronunciation/ˈθæliəm/ (THAL-ee-əm)
Appearancesilvery white
Standard atomic weight Ar, std(Tl)[204.382204.385] conventional: 204.38
Thallium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
In

Tl

Nh
mercurythalliumlead
Atomic number (Z)81
Groupgroup 13 (boron group)
Periodperiod 6
Blockp-block
Element category  post-transition metal
Electron configuration[Xe] 4f14 5d10 6s2 6p1
Electrons per shell
2, 8, 18, 32, 18, 3
Physical properties
Phase at STPsolid
Melting point577 K ​(304 °C, ​579 °F)
Boiling point1746 K ​(1473 °C, ​2683 °F)
Density (near r.t.)11.85 g/cm3
when liquid (at m.p.)11.22 g/cm3
Heat of fusion4.14 kJ/mol
Heat of vaporization165 kJ/mol
Molar heat capacity26.32 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 882 977 1097 1252 1461 1758
Atomic properties
Oxidation states−5,[1] −2, −1, +1, +2, +3 (a mildly basic oxide)
ElectronegativityPauling scale: 1.62
Ionization energies
  • 1st: 589.4 kJ/mol
  • 2nd: 1971 kJ/mol
  • 3rd: 2878 kJ/mol
Atomic radiusempirical: 170 pm
Covalent radius145±7 pm
Van der Waals radius196 pm
Color lines in a spectral range
Spectral lines of thallium
Other properties
Natural occurrenceprimordial
Crystal structurehexagonal close-packed (hcp)
Hexagonal close packed crystal structure for thallium
Speed of sound thin rod818 m/s (at 20 °C)
Thermal expansion29.9 µm/(m·K) (at 25 °C)
Thermal conductivity46.1 W/(m·K)
Electrical resistivity0.18 µΩ·m (at 20 °C)
Magnetic orderingdiamagnetic[2]
Magnetic susceptibility−50.9·10−6 cm3/mol (298 K)[3]
Young's modulus8 GPa
Shear modulus2.8 GPa
Bulk modulus43 GPa
Poisson ratio0.45
Mohs hardness1.2
Brinell hardness26.5–44.7 MPa
CAS Number7440-28-0
History
Namingafter Greek thallos, green shoot or twig
DiscoveryWilliam Crookes (1861)
First isolationClaude-Auguste Lamy (1862)
Main isotopes of thallium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
203Tl 29.5% stable
204Tl syn 3.78 y β 204Pb
ε 204Hg
205Tl 70.5% stable

Characteristics

A thallium atom has 81 electrons, arranged in the electron configuration [Xe]4f145d106s26p1; of these, the three outermost electrons in the sixth shell are valence electrons. Due to the inert pair effect, the 6s electron pair is relativistically stabilised and it is more difficult to get them involved in chemical bonding than for the heavier elements. Thus, very few electrons are available for metallic bonding, similar to the neighboring elements mercury and lead, and hence thallium, like its congeners, is a soft, highly electrically conducting metal with a low melting point of 304 °C.[8]

A number of standard electrode potentials, depending on the reaction under study,[9] are reported for thallium, reflecting the greatly decreased stability of the +3 oxidation state:[8]

+0.73 Tl3+ + 3 e ↔ Tl
−0.336 Tl+ + e ↔ Tl

Thallium is the first element in group 13 where the reduction of the +3 oxidation state to the +1 oxidation state is spontaneous under standard conditions.[8] Since bond energies decrease down the group, with thallium, the energy released in forming two additional bonds and attaining the +3 state is not always enough to outweigh the energy needed to involve the 6s-electrons.[10] Accordingly, thallium(I) oxide and hydroxide are more basic and thallium(III) oxide and hydroxide are more acidic, showing that thallium conforms to the general rule of elements being more electropositive in their lower oxidation states.[10]

Thallium is malleable and sectile enough to be cut with a knife at room temperature. It has a metallic luster that, when exposed to air, quickly tarnishes to a bluish-gray tinge, resembling lead. It may be preserved by immersion in oil. A heavy layer of oxide builds up on thallium if left in air. In the presence of water, thallium hydroxide is formed. sulfuric and nitric acid dissolve thallium rapidly to make the sulfate and nitrate salts, while hydrochloric acid forms an insoluble thallium(I) chloride layer.[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 make up nearly all of natural thallium. 204Tl is the most stable radioisotope, with a half-life of 3.78 years.[12] It is made by the neutron activation of stable thallium in a nuclear reactor.[12][13] The most useful radioisotope, 201Tl (half-life 73 hours), decays by electron capture, emitting X-rays (~70–80 keV), and photons of 135 and 167 keV in 10% total abundance;[12] therefore, it has good imaging characteristics without excessive patient radiation dose. It is the most popular isotope used for thallium nuclear cardiac stress tests.[14]

Compounds

Thallium(III)

Thallium(III) compounds resemble the corresponding aluminium(III) compounds. They are moderately strong oxidizing agents and are usually unstable, as illustrated by the positive reduction potential for the Tl3+/Tl couple. Some mixed-valence compounds are also known, such as Tl4O3 and TlCl2, which contain both thallium(I) and thallium(III). Thallium(III) oxide, Tl2O3, is a black solid which decomposes above 800 °C, forming the thallium(I) oxide and oxygen.[11]

The simplest possible thallium compound, thallane (TlH3), is too unstable to exist in bulk, both due to the instability of the +3 oxidation state as well as poor overlap of the valence 6s and 6p orbitals of thallium with the 1s orbital of hydrogen.[15] The trihalides are more stable, although they are chemically distinct from those of the lighter group 13 elements and are still the least stable in the whole group. For instance, thallium(III) fluoride, TlF3, has the β-BiF3 structure rather than that of the lighter group 13 trifluorides, and does not form the TlF
4
complex anion in aqueous solution. The trichloride and tribromide disproportionate just above room temperature to give the monohalides, and thallium triiodide contains the linear triiodide anion (I
3
) and is actually a thallium(I) compound.[16] Thallium(III) sesquichalcogenides do not exist.[17]

Thallium(I)

The thallium(I) halides are stable. In keeping with the large size of the Tl+ cation, the chloride and bromide have the caesium chloride structure, while the fluoride and iodide have distorted sodium chloride structures. Like the analogous silver compounds, TlCl, TlBr, and TlI are photosensitive.[18] The stability of thallium(I) compounds demonstrates its differences from the rest of the group: a stable oxide, hydroxide, and carbonate are known, as are many chalcogenides.[19]

The double salt Tl
4
(OH)
2
CO
3
has been shown to have hydroxyl-centred triangles of thallium, [Tl
3
(OH)]2+
, as a recurring motif throughout its solid structure.[20]

Organothallium compounds

Organothallium compounds tend to be thermally unstable, in concordance with the trend of decreasing thermal stability down group 13. The chemical reactivity of the Tl–C bond is also the lowest in the group, especially for ionic compounds of the type R2TlX. Thallium forms the stable [Tl(CH3)2]+ ion in aqueous solution; like the isoelectronic Hg(CH3)2 and [Pb(CH3)2]2+, it is linear. Trimethylthallium and triethylthallium are, like the corresponding gallium and indium compounds, flammable liquids with low melting points. Like indium, thallium cyclopentadienyl compounds contain thallium(I), in contrast to gallium(III).[21]

History

Thallium (Greek θαλλός, thallos, meaning "a green shoot or twig")[22] was discovered by flame spectroscopy in March 1861.[23] The name comes from thallium's bright green spectral emission lines.[24]

After the publication of the improved method of flame spectroscopy by Robert Bunsen and Gustav Kirchhoff[25] 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.[26][27] By 1862, Crookes was able to isolate small quantities of the new element and determine the properties of a few compounds.[28] Claude-Auguste Lamy used a spectrometer that was similar to Crookes' to determine the composition of a selenium-containing substance which was 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 by-product was available in large quantities. Lamy started to isolate the new element from that source.[29] 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 own 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 a 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.[30][31]

The dominant use of thallium was the use as poison for rodents. After several accidents the use as poison was banned in the United States by Presidential Executive Order 11643 in February 1972. In subsequent years several other countries also banned its use.[32]

Occurrence and production

Although thallium is a modestly abundant element in the Earth's crust, with a concentration estimated to be about 0.7 mg/kg,[33] mostly in association with potassium-based minerals in clays, soils, and granites, thallium is not generally economically recoverable from these sources. The major source of thallium for practical purposes is the trace amount that is found in copper, lead, zinc, and other heavy-metal-sulfide ores.[34][35]

Hutchinsonite-131710
Crystals of hutchinsonite (TlPbAs5S9)

Thallium is found in the minerals crookesite TlCu7Se4, hutchinsonite TlPbAs5S9, and lorándite TlAsS2.[36] Thallium also occurs as a trace element in iron pyrite, and thallium is extracted as a by-product of roasting this mineral for the production of sulfuric acid.[6][37]

Thallium can also be obtained from the smelting of lead and zinc ores. Manganese nodules found on the ocean floor contain some thallium, but the collection of these nodules has been prohibitively expensive. There is also the potential for damaging the oceanic environment.[38] In addition, several other thallium minerals, containing 16% to 60% thallium, occur in nature as complexes of sulfides or selenides that primarily contain antimony, arsenic, copper, lead, and/or silver. These minerals are rare, and they have had no commercial importance as sources of thallium.[33] The Allchar deposit in southern Macedonia was the only area where thallium was actively mined. This deposit still contains an estimated 500 tonnes of thallium, and it is a source for several rare thallium minerals, for example lorándite.[39]

The United States Geological Survey (USGS) estimates that the annual worldwide production of thallium is about 10 metric tonnes as a by-product from the smelting of copper, zinc, and lead ores.[33] Thallium is either extracted from the dusts from the smelter flues or from residues such as slag that are collected at the end of the smelting process.[33] The raw materials used for thallium production contain large amounts of other materials and therefore a purification is the first step. The thallium is leached either by the use of a base or sulfuric acid from the material. The thallium is precipitated several times from the solution to remove impurities. At the end it is converted to thallium sulfate and the thallium is extracted by electrolysis on platinum or stainless steel plates.[37] The production of thallium decreased by about 33% in the period from 1995 to 2009 – from about 15 metric tonnes to about 10 tonnes. Since there are several small deposits or ores with relatively high thallium content, it would be possible to increase the production if a new application, such as a hypothetical thallium-containing high-temperature superconductor, becomes practical for widespread use outside of the laboratory.[40]

Applications

Historic uses

The odorless and tasteless thallium sulfate was once widely used as rat poison and ant killer. Since 1972 this use has been prohibited in the United States due to safety concerns.[32][6] Many other countries followed this example in subsequent years. Thallium salts were used in the treatment of ringworm, other skin infections and to reduce the night sweating of tuberculosis patients. This use has been limited due to their narrow therapeutic index, and the development of improved medicines for these conditions.[41][42][43]

Optics

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.[44] Thallium(I) 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.[45]

Electronics

Thallium rod corroded
Corroded thallium rod

Thallium(I) sulfide's electrical conductivity changes with exposure to infrared light therefore making this compound useful in photoresistors.[41] Thallium selenide has been used in a bolometer for infrared detection.[46] Doping selenium semiconductors with thallium improves their performance, thus it is used in trace amounts in selenium rectifiers.[41] Another application of thallium doping is the sodium iodide crystals in gamma radiation detection devices. In these, the sodium iodide crystals are doped with a small amount of thallium to improve their efficiency as scintillation generators.[47] Some of the electrodes in dissolved oxygen analyzers contain thallium.[6]

High-temperature superconductivity

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. The research in applications started after the discovery of the first thallium barium calcium copper oxide superconductor in 1988.[48] Thallium cuprate superconductors have been discovered that have transition temperatures above 120 K. Some mercury-doped thallium-cuprate superconductors have transition temperatures above 130 K at ambient pressure, nearly as high as the world-record-holding mercury cuprates.[49]

Medical

Before the widespread application of technetium-99m in nuclear medicine, the radioactive isotope thallium-201, with a half-life of 73 hours, was the main substance for nuclear cardiography. The nuclide is still used for stress tests for risk stratification in patients with coronary artery disease (CAD).[50] This isotope of thallium can be generated using a transportable generator, which is similar to the technetium-99m generator.[51] The generator contains lead-201 (half-life 9.33 hours), which decays by electron capture to 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.[52][53]

Thallium stress test

A thallium stress test is a form of scintigraphy in which the amount of thallium in tissues correlates with tissue blood supply. Viable cardiac cells have normal Na+/K+ ion-exchange pumps. The Tl+ cation binds the K+ pumps and is transported into the cells. Exercise or dipyridamole induces widening (vasodilation) of arteries in the body. This produces coronary steal by areas where arteries are maximally dilated. Areas of infarct or ischemic tissue will remain "cold". Pre- and post-stress thallium may indicate areas that will benefit from myocardial revascularization. Redistribution indicates the existence of coronary steal and the presence of ischemic coronary artery disease.[54]

Other uses

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 alloy is used in thermometers and low-temperature switches.[41] In organic synthesis, thallium(III) salts, as thallium trinitrate or triacetate, are useful reagents for performing different transformations in aromatics, ketones and olefins, among others.[55] Thallium is a constituent of the alloy in the anode plates of magnesium seawater batteries.[6] Soluble thallium salts are added to gold plating baths to increase the speed of plating and to reduce grain size within the gold layer.[56]

A saturated solution of equal parts of thallium(I) formate (Tl(CHO2)) and thallium(I) malonate (Tl(C3H3O4)) in water is known as Clerici solution. It is a mobile, odorless liquid which changes from yellowish to colourless upon reducing the concentration of the thallium salts. With a density of 4.25 g/cm3 at 20 °C, Clerici solution is one of the heaviest aqueous solutions known. It was used in the 20th century for measuring the density of minerals by the flotation method, but its use has discontinued due to the high toxicity and corrosiveness of the solution.[57][58]

Thallium iodide is frequently used as an additive in metal-halide lamps, often together with one or two halides of other metals. It allows optimization of the lamp temperature and color rendering,[59][60] and shifts the spectral output to the green region, which is useful for underwater lighting.[61]

Toxicity

Thallium
Hazards
GHS pictograms The skull-and-crossbones pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word Danger
H300, H330, H373, H413
P260, P264, P284, P301, P310, P310[62]
NFPA 704
Flammability code 0: Will not burn. E.g., waterHealth code 4: Very short exposure could cause death or major residual injury. E.g., VX gasReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
0
4
0

Thallium and its compounds are extremely toxic, and should be handled with care. There are numerous recorded cases of fatal thallium poisoning.[63][64] The Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for thallium exposure in the workplace as 0.1 mg/m2 skin exposure over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) also set a recommended exposure limit (REL) of 0.1 mg/m2 skin exposure over an 8-hour workday. At levels of 15 mg/m2, thallium is immediately dangerous to life and health.[65]

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 by inhalation should not exceed 0.1 mg/m2 in an 8-hour time-weighted average (40-hour work week).[66] Thallium will readily absorb through the skin, and care should be taken to avoid this route of exposure, as cutaneous absorption can exceed the absorbed dose received by inhalation at the permissible exposure limit (PEL).[67] Thallium is a suspected human carcinogen.[68] For a long time thallium compounds were readily available as rat poison. This fact and that it is water-soluble and nearly tasteless led to frequent intoxication caused by accident or criminal intent.[31]

One of the main methods of removing thallium (both radioactive and normal) from humans is to use Prussian blue, a material which absorbs thallium.[69] Up to 20 grams 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 stages of the treatment, additional potassium is used to mobilize thallium from the tissues.[70][71]

According to the United States Environmental Protection Agency (EPA), man-made sources of thallium pollution include gaseous emission of cement factories, coal-burning power plants, and metal sewers. The main source of elevated thallium concentrations in water is the leaching of thallium from ore processing operations.[35][72]

See also

References

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Bibliography

External links

Boron group

The boron group are the chemical elements in group 13 of the periodic table, comprising boron (B), aluminium (Al), gallium (Ga), indium (In), thallium (Tl), and perhaps also the chemically uncharacterized nihonium (Nh). The elements in the boron group are characterized by having three electrons in their outer energy levels (valence layers). These elements have also been referred to as the triels.Boron is classified as a metalloid while the rest, with the possible exception of nihonium, are considered post-transition metals. Boron occurs sparsely, probably because bombardment by the subatomic particles produced from natural radioactivity disrupts its nuclei. Aluminium occurs widely on earth, and indeed is the third most abundant element in the Earth's crust (8.3%). Gallium is found in the earth with an abundance of 13 ppm. Indium is the 61st most abundant element in the earth's crust, and thallium is found in moderate amounts throughout the planet. Nihonium is never found in nature and therefore is termed a synthetic element.

Several group 13 elements have biological roles in the ecosystem. Boron is a trace element in humans and is essential for some plants. Lack of boron can lead to stunted plant growth, while an excess can also cause harm by inhibiting growth. Aluminium has neither a biological role nor significant toxicity and is considered safe. Indium and gallium can stimulate metabolism; gallium is credited with the ability to bind itself to iron proteins. Thallium is highly toxic, interfering with the function of numerous vital enzymes, and has seen use as a pesticide.

Isotopes of thallium

Thallium (81Tl) has 37 isotopes with atomic masses that range from 176 to 212. 203Tl and 205Tl are the only stable isotopes and 204Tl is the most stable radioisotope with a half-life of 3.78 years. 207Tl, with a half-life of 4.77 minutes, has the longest half-life of naturally occurring radioisotopes.

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.In the fully ionized state, the isotope 205Tl becomes beta-radioactive, decaying to 205Pb, but 203Tl remains stable.

Nihonium

Nihonium is a synthetic chemical element with the symbol Nh and atomic number 113. It is extremely radioactive; its most stable known isotope, nihonium-286, has a half-life of about 10 seconds. In the periodic table, nihonium is a transactinide element in the p-block. It is a member of period 7 and group 13 (boron group).

Nihonium was first reported to have been created in 2003 by a Russian–American collaboration at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, and in 2004 by a team of Japanese scientists at Riken in Wakō, Japan. The confirmation of their claims in the ensuing years involved independent teams of scientists working in the United States, Germany, Sweden, and China, as well as the original claimants in Russia and Japan. In 2015, the IUPAC/IUPAP Joint Working Party recognised the element and assigned the priority of the discovery and naming rights for the element to Riken, as it judged that they had demonstrated that they had observed element 113 before the JINR team did so. The Riken team suggested the name nihonium in 2016, which was approved in the same year. The name comes from the common Japanese name for Japan (日本, nihon).

Very little is known about nihonium, as it has only been made in very small amounts that decay away within seconds. The anomalously long lives of some superheavy nuclides, including some nihonium isotopes, are explained by the "island of stability" theory. Experiments support the theory, with the half-lives of the confirmed nihonium isotopes increasing from milliseconds to seconds as neutrons are added and the island is approached. Nihonium has been calculated to have similar properties to its homologues boron, aluminium, gallium, indium, and thallium. All but boron are post-transition metals, and nihonium is expected to be a post-transition metal as well. It should also show several major differences from them; for example, nihonium should be more stable in the +1 oxidation state than the +3 state, like thallium, but in the +1 state nihonium should behave more like silver and astatine than thallium. Preliminary experiments in 2017 showed that elemental nihonium is not very volatile; its chemistry remains largely unexplored.

Thallium(I) bromide

Thallium(I) bromide is a chemical compound of thallium and bromine with a chemical formula TlBr. It is used in room-temperature detectors of X-rays, gamma-rays and blue light, as well as in near-infrared optics.

It is a semiconductor with a band gap of 2.68 eV.The crystalline structure is of cubic CsCl type at room temperature, but it lowers to the orthorombic thallium iodide type upon cooling, the transition temperature being likely affected by the impurities. Nanometer-thin TlBr films grown on LiF, NaCl or KBr substrates exhibit a rocksalt structure.Thallium is extremely toxic and a cumulative poison which can be absorbed through the skin. Acute and chronic effects of ingesting thallium compounds include fatigue, limb pain, peripheral neuritis, joint pain, loss of hair, diarrhea, vomiting and damage to central nervous system, liver and kidneys.

Thallium(I) carbonate

Thallium(I) carbonate (Tl2CO3) is a chemical compound. It can be used for the manufacture of imitation diamonds, in chemical analysis to test for carbon disulfide, and as a fungicide. Like other thallium compounds, it is considered extremely toxic, with an oral median lethal dose of 21 mg/kg in mice. Due to its toxicity, it is listed in the United States List of Extremely Hazardous Substances as of 2007.

Thallium(I) chloride

Thallium(I) chloride, also known as thallous chloride, is a chemical compound with the formula TlCl. This colourless solid is an intermediate in the isolation of thallium from its ores. Typically, an acidic solution of thallium(I) sulfate is treated with hydrochloric acid to precipitate insoluble thallium(I) chloride. This solid crystallizes in the caesium chloride motif.The low solubility of TlCl is exploited in chemical synthesis: treatment of metal chloride complexes with TlPF6, gives the corresponding metal hexafluorophosphate derivative. The resulting TlCl precipitate is separated by filtration of the reaction mixture. The overall methodology is similar to the use of AgPF6, except that Tl+ is much less oxidizing.

The crystalline structure is of cubic caesium chloride type at room temperature, but it lowers to the orthorhombic thallium iodide type upon cooling, the transition temperature being likely affected by the impurities. Nanometer-thin TlCl films grown on KBr substrates exhibit a rocksalt structure, while the films deposited on mica or NaCl are of the regular CsCl type.A very rare mineral lafossaite, Tl(Cl,Br), is a natural form of thallium(I) chloride.Thallium(I) chloride, like all thallium compounds, is highly toxic, although its low solubility limits its toxicity.

Thallium(I) fluoride

Thallium(I) fluoride (or thallous fluoride or thallium monofluoride) is the chemical compound composed of thallium and fluorine with the formula TlF. It consists of hard white orthorhombic crystals which are slightly deliquescent in humid air but revert to the anhydrous form in dry air. It has a distorted sodium chloride (rock salt) crystal structure, due to the 6s2 inert pair on Tl+.Thallium(I) fluoride is unusual among the thallium(I) halides in that it is very soluble in water, while the others are not.

Thallium(I) hydroxide

Thallium(I) hydroxide, also called thallous hydroxide, TlOH, is a hydroxide of thallium, with thallium in oxidation state +1. Thallous hydroxide is a strong base; it is changed to thallous ion, Tl+, except in strongly basic conditions. Tl+ resembles an alkali metal ion, A+, such as Li+ or K+.

Thallium(I) oxide

Thallium(I) oxide is the inorganic compound of thallium and oxygen with the formula Tl2O in which thallium is in its +1 oxidation state. It is black and produces a basic yellow solution of thallium(I) hydroxide (TlOH) when dissolved in water. It is formed by heating solid TlOH or Tl2CO3 in the absence of air. Thallium oxide is used to make special high refractive index glass. Thallium oxide is a component of several high temperature superconductors. Thallium(I) oxide reacts with acids to make thallium(I) salts.

Tl2O adopts the anti-cadmium iodide structure in the solid state. In this way, the Tl(I) centers are pyrdamidal and the oxide centers are octahedral.

Thallium(I) oxide, like all thallium compounds, is highly toxic.

Thallium(I) sulfate

Thallium(I) sulfate (Tl2SO4) or thallous sulfate is the sulfate salt of thallium in the common +1 oxidation state, as indicated by the Roman numeral I. It is often referred to as simply thallium sulfate. Thallium(I) sulfate is colourless, odourless, tasteless, and highly toxic.

Thallium(I) sulfide

Thallium(I) sulfide, Tl2S, is a chemical compound of thallium and sulfur.

It was used in some of the earliest photo-electric detectors by T. Case who developed the so-called thalofide (sometimes spelt thallofide) cell, used in early film projectors. Case described the detector material as consisting of thallium, oxygen and sulfur, and this was incorrectly described by others as being thallium oxysulfide, which incidentally is a compound that is not known. Case's work was then built on by R.J. Cashman who recognised that the controlled oxidation of the Tl2S film was key to the operation of the cell. Cashman's work culminated in the development of long wave infrared detectors used during the Second World War. Reliable Tl2S detectors were also developed in Germany at the same time. Tl2S is found in nature as the mineral carlinite which has the distinction of being the only sulfide mineral of thallium that does not contain at least two metals. Tl2S has a distorted anti-CdI2 structure.

Tl2S can be prepared from the elements or by precipitating the sulfide from a solution of thallium(I), e.g. the sulfate or nitrate. Thin films have been deposited, produced from a mixture of citratothallium complex and thiourea. Heating the film in nitrogen at 300°C converts all the product into Tl2S

Thallium(I) telluride

Thallium(I) telluride (Tl2Te) is a chemical compound of thallium and tellurium. It has a structure related to that of Tl5Te3. This compound is not well characterized. Its existence has only recently been confirmed by differential scanning calorimetry.

Thallium(III) hydroxide

Thallium(III) hydroxide, Tl(OH)3, also known as thallic hydroxide, is a hydroxide of thallium. It is a white solid.

Thallium(III) hydroxide is a very weak base; it is changed to thallium(III) ion, Tl3+, only in strongly acid conditions.

Thallium(III) nitrate

Thallium(III) nitrate, also known as thallic nitrate, is a thallium compound with chemical formula Tl(NO3)3. It is normally found as the trihydrate. It is a colorless and highly toxic solid. It is a strong oxidizing agent useful in organic synthesis. Among its many transformations, it oxidizes methoxyl phenols to quinone acetals, alkenes to acetals, and cyclic alkenes to ring-contracted aldehydes.

Thallium(III) oxide

Thallium(III) oxide, also known as thallic oxide, is a chemical compound of thallium and oxygen. It occurs in nature as the rare mineral avicennite. Its structure is related to that of Mn2O3 which has a bixbyite like structure. Tl2O3 is metallic with high conductivity and is a degenerate n-type semiconductor which may have potential use in solar cells.

A method of producing Tl2O3 by MOCVD is known. Any practical use of thallium(III) oxide will always have to take account of thallium's poisonous nature. Contact with moisture and acids may form poisonous thallium compounds.

Thallium halides

The thallium halides include monohalides, where thallium has oxidation state +1, trihalides where thallium generally has oxidation state +3 and some intermediate halides with mixed +1 and +3 oxidation states. These materials find use in specialized optical settings, such as focusing elements in research spectrophotometers. Compared to the more common zinc selenide-based optics, materials such as thallium bromoiodide enable transmission at longer wavelengths. In the infrared, this allows for measurements as low as 350 cm−1 (28 µm), whereas zinc selenide is opaque by 21.5 µm and ZnSe optics are generally only usable to 650 cm−1 (15 µm).

Thallium hydride

Thallium hydride (systematically named thallium trihydride) is an inorganic compound with the empirical chemical formula TlH3. It has not yet been obtained in bulk, hence its bulk properties remain unknown. However, molecular thallium hydride has been isolated in solid gas matrices. Thallium hydride is mainly produced for academic purposes.

Thallium hydride is the simplest thallane. Thallium is the heaviest member of the Group 13 metals; the stability of group 13 hydrides decreases with increasing periodic number. This is commonly attributed to poor overlap of the metal valence orbitals with that of the 1s orbital of Hydrogen. Despite encouraging early reports, it is unlikely that a thallium hydride species has been isolated. Thallium hydrides have been observed only in matrix isolation studies; the infrared spectrum was obtained in the gas phase by laser ablation of thallium in the presence of hydrogen gas. This study confirmed aspects of ab initio calculations conducted by Schwerdtfeger which indicated the similar stability of thallium and indium hydrides. There has not been a confirmed isolation of a thallium hydride complex to date.

Thallium poisoning

Thallium poisoning is poisoning due to thallium and its compounds which are often highly toxic. Contact with skin is dangerous, and adequate ventilation should be provided when melting this metal. Many thallium(I) compounds are highly soluble in water 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 (due to similar ionic radii). It can thus enter the body via potassium uptake pathways. Other aspects of thallium's chemistry differ strongly from that of the alkali metals, such as its high affinity for sulfur ligands. Thus, this substitution disrupts many cellular processes by interfering with the function of proteins that incorporate cysteine, an amino acid containing sulfur. 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 hair loss (which led 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), although the loss of hair only generally occurs in low doses; in high doses the thallium kills before this can take effect. Thallium was once an effective murder weapon before its effects became understood and an antidote (Prussian blue) discovered. Indeed, thallium poisoning has been called the "poisoner's poison" since thallium is colorless, odorless and tasteless; its slow-acting, painful and wide-ranging symptoms are often suggestive of a host of other illnesses and conditions.

Thallous acetate

Thallous acetate is a salt of thallium and acetate with the chemical formula TlCH3COO. It is used in microbiology as a selective growth medium. It is poisonous.

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