Name Thallium
Symbol Tl
Atomic Number 81
Atomic Mass 204.3833 atomic mass units
Number of Protons 81
Number of Neutrons 123
Number of Electrons 81
Melting Point 303.5 C
Boiling Point 1457.0 C
Density 11.85 grams per cubic centimeter
Normal Phase Solid
Family Transition Metals
Period 6
Cost $40 per pound



Origin of Name From the Greek word thallus, meaning young shoot
Date and Place of Discovery Discovered in 1861 in England; isolated in 1862
Discovered by Discovered by Sir William Crookes
Isolated by Crookes and Claude-Auguste Lamy
Common Compounds
Interesting facts
  • It and its compounds are very toxic.
  • It is suspected as a human carcinogen.
  • It has a metallic luster when it is first exposed to air but it tarnish quickly.
  • When left in air, oxide is created.
Common Uses
  • Rat and ant poisons
  • Infrared radiation detection
  • Glasses with high refraction
  • Semiconductors
  • Photocells
  • Treatment of ringworm and other skin infections
  • Nuclear medicine
  • Super conducting materials
  • Magnetic resonance imaging


Photo Courtesy of
Chemical Elements
Los Alamos National Labs
Mrs. Purdy's Web Page

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