Thallium Facts

Chemical & Physical Properties

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Thallium Basic Facts

Atomic Number: 81

Symbol: Tl

Atomic Weight: 204.3833

Discovery: Crookes 1861

Electron Configuration: [Xe] 4f14 5d10 6s2 6p1

Element Classification: metal

Discovered By: Sir William Crookes

Discovery Date: 1861 (England)

Name Origin: Greek: thallos (green twig), named for a bright green line in its spectrum.

Thallium Physical Data

Density (g/cc): 11.85

Melting Point (°K): 576.6

Boiling Point (°K): 1730

Appearance: soft bluish-gray metal

Atomic Radius (pm): 171

Atomic Volume (cc/mol): 17.2

Covalent Radius (pm): 148

Ionic Radius: 95 (+3e) 147 (+1e)

Specific Heat (@20°C J/g mol): 0.128

Fusion Heat (kJ/mol): 4.31

Evaporation Heat (kJ/mol): 162.4

Thermal Conductivity: 46.1 J/m-sec-deg

Debye Temperature (°K): 96.00

Pauling Negativity Number: 1.62

First Ionizing Energy (kJ/mol): 588.9

Oxidation States: 3, 1

Lattice Structure: hexagonal

Lattice Constant (Å): 3.460

Lattice C/A Ratio: 1.599

Uses: infrared detectors, photomultipliers

Source: obtained as a by-product of Zn/Pb smelting

References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952)

Periodic Table of the Elements

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Helmenstine, Anne Marie, Ph.D. "Thallium Facts." ThoughtCo, Mar. 11, 2017, Helmenstine, Anne Marie, Ph.D. (2017, March 11). Thallium Facts. Retrieved from Helmenstine, Anne Marie, Ph.D. "Thallium Facts." ThoughtCo. (accessed January 17, 2018).