Thallium
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.
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)
