thalliums

Thallium is a chemical element with the symbol Tl and atomic number 81. It is a soft, silvery post-transition metal in group 13, known for tarnishing in air. Its melting point is about 304°C and its boiling point exceeds 1,400°C, giving it a relatively wide liquid range for a metal.

In nature thallium is extremely rare and occurs only in trace amounts. Commercial thallium is produced mainly as a byproduct of refining zinc and copper ores, and from certain sulfide minerals.

Chemically, thallium most often exists in the +1 oxidation state (Tl(I)) in salts, while +3 compounds are less common and more oxidizing. Natural thallium comprises two stable isotopes, Tl-203 and Tl-205.

Uses include thallium-doped materials for electronics and optics. Tl-doped sodium iodide (NaI(Tl)) is a widely used scintillator in radiation detectors, and the radionuclide Tl-201 is used in myocardial perfusion imaging. Historically, thallium salts were once used as rodenticides and insecticides, though safety concerns have led to restrictions.

Toxicity and safety: Thallium compounds are highly toxic; exposure can cause hair loss, nerve damage, and organ injury. Handling requires strict safety procedures, proper disposal, and regulatory compliance; environmental releases are tightly controlled.

Thallium was discovered in 1861 by William Crookes and Claude-Auguste Lamy, and named for the green spectral lines observed in its emission spectrum, from the Greek thallos, meaning green shoot.