Quick Facts
| Property | Value |
|---|---|
| Symbol | Tl |
| Atomic Number | 81 |
| Atomic Mass | 204.38 u |
| Category | Post-Transition Metal |
| Period | 6 |
| Group | 13 |
| Block | p |
| Electron Configuration | [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹ |
History and Discovery
Discovered by: William Crookes Year of Discovery: 1861 Location: London, England
Etymology
From Greek "thallos" meaning "green shoot," due to its bright green spectral line.
Applications and Uses
- Thallium-201 for cardiac imaging
- Low-temperature thermometers
- Infrared detectors
- Specialty glass (high refractive index)
- Historically used as rat poison (now banned)
Toxicity
Thallium is extremely toxic. It was once used as a murder weapon because it is colorless, odorless, and tasteless.
Interesting Facts
- Called "the poisoner's poison" due to its undetectable nature
- Agatha Christie featured it in "The Pale Horse"
- Now heavily regulated due to toxicity
- Discovered by its green spectral line
- Bioaccumulates and is extremely dangerous