Symbol: Tl
Atomic Number: 81
Atomic Weight: 204.3833
Element Classification: Other Metal
Discovered By: Sir William Crookes
Discovery Date: 1861 (England)
Name Origin: Greek: thallos (green twig), for a bright green line in its spectrum.

Density (g/cc): 11.85
Melting Point (K): 576.6
Boiling Point (K): 1730
Appearance: Soft, gray metal
Atomic Radius (pm): 171
Atomic Volume (cc/mol): 17.2
Covalent Radius (pm): 148
Ionic Radius: 95 (+3e) 147 (+1e)
Specific Heat (@20C J/g mol): 0.128
Fusion Heat (kJ/mol): 4.31
Evaporation Heat (kJ/mol): 162.4
Thermal Conductivity (@25C W/m K):
Debye Temperature (K): 96.00
Pauling Negativity Number: 1.62
First Ionizing Energy (kJ/mol): 588.9
Oxidation States: 3, 1
Electronic Configuration: [Xe] 4f14 5d10 6s2 6p1
Lattice Structure: Hexagonal (HEX)
Lattice Constant (): 3.460
Lattice C/A Ratio: 1.599

Mineral Hardness [no units]: 1.2
Brinell Hardness [/MN m-2]: 26.4

Note: Thallium is soft and have a low recrystallization temperature. Pressure during grinding and polishing, and heating through ftiction should be as low as possible; otherwise deformed layers may form or fictious microstructures may be observed. Thallium is toxic.

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