Quick answerThallium (Tl) is a post-transition metal with atomic number 81 and an atomic mass of 204.38 (2023), in group 13, period 6. It was discovered by William Crookes in 1861. It is used for electronics and heart imaging. Its electron configuration is [Xe] 4f14 5d10 6s2 6p1.
Thallium is a soft, toxic metal once used as rat poison, now confined to electronics and medical heart scans.
Key facts
| Symbol | Tl |
|---|---|
| Atomic number | 81 |
| Atomic mass | 204.38 (IUPAC standard atomic weight, 2023) |
| Category | post-transition metal |
| Group | 13 |
| Period | 6 |
| Block | p-block |
| Electron configuration | [Xe] 4f14 5d10 6s2 6p1 |
| Discovered | William Crookes, 1861 |
| Uses | electronics, heart imaging, infrared detectors, high-temperature superconductors, glass manufacturing |
Quick quiz
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Keep exploring
- Periodic table — all 118 elements
- Gallium (Ga) — another post-transition metal, atomic number 31
- Indium (In) — another post-transition metal, atomic number 49
- Tin (Sn) — another post-transition metal, atomic number 50
- Lead (Pb) — another post-transition metal, atomic number 82
- Bismuth (Bi) — another post-transition metal, atomic number 83
- Polonium (Po) — another post-transition metal, atomic number 84
- Nihonium (Nh) — another post-transition metal, atomic number 113
- Flerovium (Fl) — another post-transition metal, atomic number 114
- Moscovium (Mc) — another post-transition metal, atomic number 115
- Livermorium (Lv) — another post-transition metal, atomic number 116
- All post-transition metal elements — on the periodic table
Sources & last updated
- CIAAW — Standard Atomic Weights
- PubChem Periodic Table
- Wikipedia — Timeline of chemical element discoveries
Last updated: . Figures are shown with their year; where sources disagree, the value is left out rather than estimated.