81
204.38
Tl
Thallium
Identification
CAS Number: 7440-28-0
Discovery Year: 1861
Discoverer: Sir William Crookes
Discovery Location: England
Properties
Atomic Dimensions
Atomic Radius: 190 pm →
Atomic Radius (Rahm): 242 pm
Covalent Radius: 145 pm →Van der Waals Radius: 196 pm
Metallic Radius: 144 pm
Atomic Volume: 17.2 cm³/mol
Lattice Constant: 3.46 Å
Thermodynamics
Electronic Structure
Electron Config: [Xe] 4f14 5d10 6s2 6p
Block: p
Period: 6 →Group: 13 →Electronegativity: 1.8 →Electron Affinity: 0.377 eV →Oxidation States: +1, +3
Abundance & Geochemistry
Crust Abundance: 0.85 mg/kg
Sea Abundance: 0.000019 mg/L
Goldschmidt Class: chalcophile
About
Pure, unreacted thallium appears silvery-white and exhibits a metallic lustre. Upon reacting with air, it begins to turn bluish-grey and looks like lead. It is very malleable, and can be cut with a knife. There are two stable isotopes, and four radioisotopes, Tl-204 being the most stable with a half-life of 3.78 years. Thallium sulphate was used as a rodenticide. Thallium sulphine's conductivity changes with exposure to infrared light, this gives it a use in infrared detectors. Discovered by Sir William Crookes via spectroscopy. Its name comes from the Greek word thallos, which means green twig. Thallium and its compounds are toxic and can cause cancer.
Isotopes
Tl-205 205 70.41%
Tl-203 203 29.44%