Thallium (Tl)

Thallium is a soft, gray post-transition metal that is not found free in nature.

Core Principles & Analysis

• William Crookes discovered thallium spectroscopically in 1861 by its bright green line, naming it from the Greek for a green shoot.
• Its colorless, nearly tasteless toxic salts earned it the nickname 'the poisoner's poison' before sales were restricted.
• Thallium-201 is used in cardiac stress-test imaging, and thallium compounds appear in infrared optics and low-temperature thermometers.

Specifications & Metrics

• NUM: 81
• SYMBOL: Tl
• CATEGORY: Post-transition Metal
• ATOMIC MASS: 204.383 u
• ELECTRONEGATIVITY: 1.62 Pauling
• ATOMIC RADIUS: 196 pm
• IONIZATION ENERGY: 6.108 eV
• ELECTRON AFFINITY: 0.2 eV
• MELTING POINT: 577 K
• BOILING POINT: 1746 K
• DENSITY: 11.8 g/cm³
• ELECTRON CONFIGURATION: [Xe]6s2 4f14 5d10 6p1
• OXIDATION STATES: +3, +1
• STANDARD STATE: Solid
• GROUP BLOCK: Post-transition metal
• YEAR DISCOVERED: 1861