T

Thallium

IUPAC: Thallium

Tl Elements CAS 7440-28-0
Quick Reference
Formula / NotationTl
CAS Number7440-28-0
Molecular Weight204.38
Melting Point304.0
Boiling Point1473.0
Density11.85
SolubilitySlightly soluble (soluble as Tl+ salts)
AppearanceSoft, silvery-grey metal
Also Known AsTl, thallium metal
CategoryElements

What is Thallium?

Thallium is a soft, grey post-transition metal, atomic number 81. Extremely toxic - tasteless, odourless thallium salts have been used as rat poison and murder weapon. Thallium-201 is used in cardiac stress tests in nuclear medicine.

Formula & Notation

Tl

IUPAC Name: Thallium

Other Names / Synonyms: Tl, thallium metal

Properties & Characteristics

Atomic number: 81. Atomic mass: 204.38 g/mol. Period 6, Group 13. Melting point: 304 C. Boiling point: 1473 C. Density: 11.85 g/cm3. Electronegativity: 1.62. Oxidation states: +1, +3. Two stable isotopes: Tl-203 (29.5%), Tl-205 (70.5%).

Physical Data

PropertyValue
Melting Point304.0
Boiling Point1473.0
Density11.85
Molecular Weight204.38
SolubilitySlightly soluble (soluble as Tl+ salts)
AppearanceSoft, silvery-grey metal

Uses & Applications

Tl-201 cardiac SPECT imaging (stress tests). Infrared optics (thallium bromide-iodide). Thallium doped caesium iodide scintillators. Rodenticide (now mostly banned). Superconductors (Tl-Ba-Ca-Cu-O). Low-melting glass.

Safety Information

Extremely toxic - LD50 ~15 mg/kg. Tl+ ions mimic K+ - disrupts potassium-dependent processes. Causes hair loss, peripheral neuropathy, organ failure. Tasteless and odourless - classic untraceable poison. Thallium-201: low-level radioactive, radiation precautions needed. Strict regulatory control in most countries.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Thallium
Formula Tl
CAS Number 7440-28-0
Molecular Weight 204.38
Category Elements
Synonyms Tl, thallium metal

Frequently Asked Questions

Thallium is a soft, grey post-transition metal, atomic number 81. Extremely toxic - tasteless, odourless thallium salts have been used as rat poison and murder weapon. Thallium-201 is used in cardiac stress tests in nuclear medicine.

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