Element 81
Thallium
Post-transition metals
Thallium (Tl) is in the p-block of the periodic table — group 13, period 6.
Thallium is a chemical element with symbol Tl and atomic number 81.
Key data
- Atomic number
- 81
- Atomic mass
- 204.380 u
- Group / Period
- 13 / 6
- Block
- p-block
- Phase at STP
- Solid
- Density
- 11.85 g/cm³
- Melting point
- 303.9 °C
- Boiling point
- 1472.8 °C
- Electron configuration
- [Xe] 4f14 5d10 6s2 6p1
Periodic table block
Thallium is in the p-block (group 13, period 6). Elements land in the p-block when their highest-energy electrons fill a p subshell — this region holds most nonmetals, the metalloids, and the metals on the right of the table.
New to this? Periodic table blocks explained: s, p, d, and f
Common uses
- •Rat poison (banned)
- •Infrared detectors
- •Heart imaging
Discovery
Year: 1861
Discovered by: William Crookes
Frequently asked questions
What is the atomic number of Thallium?
Thallium has atomic number 81. Its symbol is Tl and its atomic mass is 204.38 u.
What category of element is Thallium?
Thallium is classified as post-transition metals. It sits in group 13, period 6 of the periodic table.
What block of the periodic table is Thallium in?
Thallium is in the p-block (group 13, period 6). Its highest-energy electrons occupy the p subshell — you can see this in its electron configuration, [Xe] 4f14 5d10 6s2 6p1.
What is Thallium used for?
Common uses of Thallium include: Rat poison (banned), Infrared detectors, Heart imaging.
When was Thallium discovered?
Thallium was discovered in 1861 by William Crookes.
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