Atomic number: 81
Category: transition metal
Density at 25°C: solid: density: 11.85 g·cm−3
Well after the excitement of mercury thallium is almost back to the usual elements, but it is very soft indeed and can be cut easily with a knife. Thallium compounds are used in optics and were used in poisons. So thallium tends to be pretty toxic.
Use, natural applications or common combinations:
- mercury-thallium alloy for cold thermometers that won't freeze until -60°C
- optical photoresistors
- Standard atomic weight: [204.382; 204.385]
- Melting point: 304 °C
- Boiling point: 1473 °C
- Radioactivity: all naturally stable. Some isotopes have very long half lives.