Thallium (Tl) Elemental Symbol

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Thallium(Tl) atomic and molecular weight, atomic number and elemental symbolThallium is a post-transition metal that is not found free in nature. It is a Block P, Group 13, Period 6 element. Thallium Bohr ModelThe number of electrons in each of Thallium's shells is 2, 8, 18, 32, 18, 3 and its electron configuration is [Xe] 4f14 5d10 6s2 6p1. The Thallium atom has a radius of and its Van der Waals radius is Elemental ThalliumIn its elemental form, CAS 7440-28-0, thallium has a silvery white appearance. Thallium was first discovered by Sir William Crookes in 1861 and gets its name from the Greek word "thallos" which means twig or green shoot. Thallium is produced from trace amounts that are found in copper, lead, zinc, and other heavy-metal-sulfide ores. Thallium information, including technical data, safety data, high purity properties, research, applications and other useful facts are discussed below. Scientific facts such as the atomic structure, ionization energy, abundance on earth, conductivity and thermal properties are also included.

Thallium is primarily used for its electrical conductivity as thallium sulfide which changes with exposure to infrared light. High Purity (99.999%) Thallium Oxide (Tl2O) PowderThis ability makes the compound useful in photocells. Thallium bromide-iodide crystals have been used as infrared optical materials. Thallium has also been used with sulfur, selenium or arsenic to produce low melting glasses which become fluid between 125° and 150 C°. High Purity (99.999%) Thallium (Tl) Sputtering TargetThese glasses have properties at room temperatures similar to ordinary glasses and are said to be durable and insoluble in water. Thallium oxide has been used to produce glasses with a high index of refraction, and is also used in the manufacture of photo cells. Oxides are available in forms including powders and dense pellets for such uses as optical coating and thin film applications. Thallium is also available in many other specific states, forms and shapes including pellets, rod, wire and granules for evaporation source material purposes. Nanoparticles and nanopowders provide ultra-high surface area which nanotechnology research and recent experiments demonstrate function to create new and unique properties and benefits.

Thallium and its compounds are highly toxic. Safety data for Thallium metal, nanoparticles and its compounds can vary widely depending on the form. For potential hazard information, toxicity, and road, sea and air transportation limitations, such as DOT Hazard Class, DOT Number, EU Number, NFPA Health rating and RTECS Class, please see the specific Thallium material or compound referenced in the “Thallium Products” tab below.

  • Properties
  • Safety Data
  • Products
  • Research
  • Isotopes
  • Other Elements

Thallium Properties

Symbol: Tl Melting Point: 577 K, 304 °C, 579 °F
Atomic Number: 81 Boiling Point: 1746 K, 1473 °C, 2683 °F
Atomic Weight: 204.3833 Density: 11.85 g·cm−3
Element Category: post-transition metal Liquid Density @ Melting Point: 11.22 g·cm−3
Group, Period, Block: 13, 6, p Specific Heat: 129 J/(kg K)
    Heat of Vaporization 166.1 kJ mol-1
CHEMICAL STRUCTURE Heat of Fusion 4.31 kJ mol-1
Electrons: 81 Thermal Conductivity: 46.1 W·m−1·K−1
Protons: 81 Thermal Expansion: (25 °C) 29.9 µm·m−1·K−1
Neutrons: 123 Electrical Resistivity: (20 °C) 0.18 µΩ·m
Electron Configuration: Xe 4f14 5d10 6s2 6p1 2, 8, 18, 32, 18, 3 Electronegativity: 1.62 (Pauling scale)
Atomic Radius: 170 pm Tensile Strength:  
Covalent Radius: 145±7 pm Molar Heat Capacity: 26.32 J·mol−1·K−1
Van der Waals radius: 196 pm Young's Modulus: 8 GPa
Oxidation States: 3, 2, 1 (mildly basic oxide) Shear Modulus: 2.8 GPa
Phase: Solid Bulk Modulus: 43 GPa
Crystal Structure: hexagonal close-packed Poisson Ratio: 0.45
Magnetic Ordering: diamagnetic Mohs Hardness: 1.2
1st Ionization Energy: 589.36 kJ mol-1 Vickers Hardness: N/A
2nd Ionization Energy: 1971.02 kJ mol-1 Brinell Hardness: 26.4 MPa
3rd Ionization Energy: 2878.18 kJ mol-1 Speed of Sound: (20 °C) 818 m·s−1
CAS Number: 7440-28-0 Abundance in typical human body, by weight: N/A
ChemSpider ID: 4514293 Abundance in typical human body, by atom: N/A
PubChem CID: 5359464 Abundance in universe, by weight: 0.5 ppb
MDL Number: MFCD00134063 Abundance in universe, by atom: 0.003 ppb
EC Number: 231-138-1 Discovered By: William Crookes
Beilstein Number: N/A Discovery Date: 1861
SMILES Identifier: [Tl]  
InChI Identifier: InChI=1S/Tl Other Names:  

Health, Safety & Transportation Information for Thallium

Material Safety Data Sheet MSDS
Signal Word Danger
Hazard Statements H300-H330-H373-H413
Hazard Codes T+
Risk Codes 26/28-33-53
Safety Precautions 13-28-45-61
RTECS Number XG3425000
Transport Information UN 3288 6.1/PG 2
WGK Germany 3
Globally Harmonized System of
Classification and Labelling (GHS)
Skull and Crossbones-Acute Toxicity  Health Hazard  

Thallium Products

Metal Forms  •  Compounds  •  Oxide Forms  •  Organometallic Compounds
Sputtering Targets  •  Nanomaterials  •  Semiconductor Materials •  Isotopes

Recent Research & Development for Thallium

  • A case of severe thallium poisoning successfully treated with hemoperfusion and continuous veno-venous hemofiltration. Huang C, Zhang X, Li G, Jiang Y, Wang Q, Tian R. Hum Exp Toxicol. 2014.
  • Phytoremediation of Water Polluted by Thallium, Cadmium, Zinc, and Lead with the Use of Macrophyte Callitriche cophocarpa. Augustynowicz J, Tokarz K, Baran A, Plachno BJ. Arch Environ Contam Toxicol. 2014.
  • Comparison of urinary thallium levels in non-occupationally exposed people and workers. Staff JF, Cotton RJ, Warren ND, Morton J. Int Arch Occup Environ Health. 2014.
  • Formic acid electrooxidation on thallium-decorated shape-controlled platinum nanoparticles: an improvement in electrocatalytic activity. Busó-Rogero C, Perales-Rondón JV, Farias MJ, Vidal-Iglesias FJ, Solla-Gullon J, Herrero E, Feliu JM. Phys Chem Chem Phys. 2014.
  • Misdiagnosis and long-term outcome of 13 patients with acute thallium poisoning in China. Li JM, Wang W, Lei S, Zhao LL, Zhou D, Xiong H. Clin Toxicol (Phila). 2014.
  • Distributions and concentrations of thallium in surface waters of a region impacted by historical metal mining (Cornwall, UK). Tatsi K, Turner A. Sci Total Environ. 2014.
  • Synthesis and structural characterization of tris(2-pyridonyl)methyl complexes of zinc and thallium: a new class of metallacarbatranes and a monovalent thallium alkyl compound. Al-Harbi A, Rong Y, Parkin G. Dalton Trans.
  • Role of multimodality imaging including Thallium-201 myocardial perfusion imaging in the diagnosis and monitoring of treatment response in cardiac sarcoidosis. Surasi DS, Manapragada PP, Lloyd SG, Bhambhvani P. J Nucl Cardiol. 2014.
  • Influence of left ventricular geometry on thallium-201 gated single-photon emission tomographic findings in patients with known or suspected coronary artery disease. Kurisu S, Iwasaki T, Ikenaga H, Watanabe N, Higaki T, Shimonaga T, Ishibashi K, Mitsuba N, Dohi Y, Kihara Y. Ann Nucl Med. 2014.
  • Influence of the cavity size of water-soluble cryptophanes on their binding properties for cesium and thallium cations. Brotin T, Goncalves S, Berthault P, Cavagnat D, Buffeteau T. J Phys Chem B.
  • Benzannulated tris(2-mercapto-1-imidazolyl)hydroborato ligands: tetradentate ?(4)-S3H binding and access to monomeric monovalent thallium in an [S3] coordination environment. Rong Y, Palmer JH, Parkin G. Dalton Trans. 2014 Jan.
  • Thallium(I) sorption using Prussian blue immobilized in alginate capsules. Vincent T, Taulemesse JM, Dauvergne A, Chanut T, Testa F, Guibal E. Carbohydr Polym. 2014.
  • Enhancement of lanthanide evaporation by complexation: Dysprosium tri-iodide mixed with indium iodide and thulium tri-iodide mixed with thallium iodide. Curry JJ, Estupiñán EG, Henins A, Lapatovich WP, Shastri SD, Hardis JE. J Chem Phys.
  • [Thallium poisoning in an adolescent girl]. López Segura N, Aznar Laín G, Nolla Salas J, Mur Sierra A. Med Clin (Barc). 2013 Dec.
  • Evaluation of cytogenetic and DNA damage caused by thallium(I) acetate in human blood cells. Rodríguez-Mercado JJ, Hernández-de la Cruz H, Felipe-Reyes M, Jaramillo-Cruz E, Altamirano-Lozano MA. Environ Toxicol. 2013 Dec.
  • Influence of the Cavity Size of Water-Soluble Cryptophanes on Their Binding Properties for Cesium and Thallium Cations. Buffeteau T, Goncalves S, Berthault P, Cavagnat D, Brotin T. J Phys Chem B. | first author:Buffeteau T
  • Nondestructive method for quantifying thallium dopant concentrations in CsI:Tl crystals. Miller SR, Ovechkina EE, Bennett P, Brecher C. Appl Radiat Isot. 2013 Dec.
  • Preoperative Cardiac Evaluation by Dipyridamole Thallium-201 Myocardial Perfusion Scan Provides no Benefit in Patients with Abdominal Aortic Aneurysm. Shin S, Kwon TW, Cho YP, Lee JY, Park H, Han Y. World J Surg.
  • Alsobacter metallidurans gen. nov., sp. nov., a thallium-tolerant soil bacterium in the order Rhizobiales. Zhihua B, Sato Y, Fujimura R, Ohta H. Int J Syst Evol Microbiol.
  • Thallium(I) complexes of fluorinated bis- and tris(pyrazolyl)borate ligands: [H2B{3,5-(CF3)2pz}2]Tl and [HB{3,5-(CF3)2pz}3]Tl. Dias HV, Thankamani J. Acta Crystallogr C. | first author:Dias HV

Thallium Isotopes

Thallium (Tl) has 37 isotopes with atomic masses ranging from 176 to 212. Only 203Tl and 205Tl are stable.

Nuclide Symbol Isotopic Mass Half-Life Nuclear Spin
203Tl 202.9723442 Stable 1/2+
205Tl 204.9744275 Stable 1/2+