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

  • C. Karunakaran, S. Kalaivani, Enhanced visible light-photocatalysis by hydrothermally synthesized thallium-doped bismuth vanadate nanoparticles, Materials Science in Semiconductor Processing, Volume 27, November 2014
  • Remigijus Ivanauskas, Linas Samardokas, Marius Mikolajunas, Darius Virzonis, Jonas Baltrusaitis, Polyamide–thallium selenide composite materials via temperature and pH controlled adsorption–diffusion method, Applied Surface Science, Volume 317, 30 October 2014
  • Wen Liu, Pan Zhang, Alistair G.L. Borthwick, Hao Chen, Jinren Ni, Adsorption mechanisms of thallium(I) and thallium(III) by titanate nanotubes: Ion-exchange and co-precipitation, Journal of Colloid and Interface Science, Volume 423, 1 June 2014
  • Sudha Rana, Navneet Sharma, Himanshu Ojha, Hosakote Gurumalappa Shivkumar, Sarwat Sultana, Rakesh Kumar Sharma, p-Tertbutylcalix[4]arene nanoemulsion: Preparation, characterization and comparative evaluation of its decontamination efficacy against Technetium-99m, Iodine-131 and Thallium-201, Colloids and Surfaces B: Biointerfaces, Volume 117, 1 May 2014
  • M. Bokova, I. Alekseev, D. Kalyagin, V. Tsegelnik, Yu. Ermolenko, E. Bychkov, 204Tl tracer diffusion and conductivity in thallium thiogermanate glasses, Solid State Ionics, Volume 253, 15 December 2013
  • G.S. Sivagurunathan, K. Ramalingam, C. Rizzoli, Nanothallium(III) sulfide from dithiocarbamate precursors: Synthesis, single crystal X-ray structures and characterization, Polyhedron, Volume 65, 28 November 2013
  • I. Mucha, Reinvestigation of phase equilibria in the thallium(I) selenide–antimony(III) selenide system, Thermochimica Acta, Volume 563, 10 July 2013
  • Maryam Mohammadi, Kamran Akhbari, Younes Hanifehpour, Ali Morsali, Sang Woo Joo, Giuseppe Bruno, Hadi Amiri Rudbari, Synthesis of one-dimensional Tl2O3 nano-structures from thermolyses of a new two-dimensional thallium(I) supramolecular polymer with secondary polyhapto Tl?C interactions, Journal of Organometallic Chemistry, Volume 733, 1 June 2013
  • Saeed ur Rehman, Najeeb Ullah, Ali Reza Kamali, Khurshid Ali, Cemile Yerlikaya, Hanif ur Rehman, Study of thallium (III) adsorption onto multiwall carbon nanotubes, Carbon, Volume 55, April 2013
  • I. Mucha, Phase diagram for the quasi-binary thallium(I) selenide–indium(III) selenide system, Thermochimica Acta, Volume 550, 20 December 2012

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+