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