Tl
204.380Thallium
Talyum
Thallium is a highly toxic post-transition metal with atomic number 81. It is known for thallium-201 myocardial perfusion SPECT imaging, thallium bromide radiation detectors, NaI(Tl) scintillators and the inert pair effect.
81
204.38 g/mol
[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹
2 | 8 | 18 | 32 | 18 | 3
1.62
11.85 g/cm³
303.9 °C
1472.8 °C
William Crookes
Thallium was discovered in 1861 by William Crookes from a bright green spectral line in residues from sulfuric acid production. Its name comes from the Greek thallos, meaning green shoot, and Claude-Auguste Lamy soon isolated the metal.
Thallium-201
Half-life: About 73 hours. Artificial radioisotope used in myocardial perfusion SPECT imaging.Thallium-203
Natural abundance: About 29.5%. Stable natural thallium isotope.Thallium-205
Natural abundance: About 70.5%. Dominant stable natural thallium isotope.TlBr
Thallium(I) BromideRoom-temperature radiation detector crystal.NaI(Tl)
Thallium-Doped Sodium IodideCommon gamma scintillation detector material.Tl₂SO₄
Thallium(I) SulfateHistorical rodenticide; highly toxic and now restricted or banned.TlCl
Thallium(I) ChlorideThallium chemistry precursor and radioisotope formulation context.- Thallium-201 chloride for myocardial perfusion SPECT and cardiac viability imaging
- Thallium bromide and iodide crystals for room-temperature radiation detectors
- NaI(Tl) scintillation crystals for gamma-ray detection
- Low-temperature mercury-thallium alloys in historical thermometer applications
- Thallium sulfate as a historical rodenticide, now banned or restricted in many places
Thallium has no essential biological role and is highly toxic. Tl⁺ can mimic potassium ions in some biological transport systems, which helps explain its neurological and systemic toxicity.
- Thallium poisoning can be difficult to recognize because it may be colorless, tasteless and delayed in symptoms.
- Prussian blue is used as an antidote because it can bind thallium ions in the gut and reduce reabsorption.
- Thallium often prefers the +1 oxidation state because of the inert pair effect on the 6s² electrons.
- Thallium-201 behaves partly like potassium in heart tissue, which is why it can map myocardial perfusion.
- Thallium has atomic number 81 and symbol Tl.
- Its electron configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹.
- The +1 oxidation state is especially important because of the inert pair effect.
- Remember thallium for toxicity, Tl-201 SPECT and NaI(Tl) scintillators.
What is the atomic number of thallium?
The atomic number of thallium is 81.
What is the electron configuration of thallium?
Thallium has the electron configuration [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹.
What is thallium used for?
Thallium is used in Tl-201 medical imaging, radiation detector crystals, NaI(Tl) scintillators and some specialized materials.
Why is thallium toxic?
Thallium ions can interfere with potassium-dependent biological processes and damage the nervous system and other organs.
What is thallium-201 used for?
Thallium-201 is used in myocardial perfusion imaging to evaluate blood flow and viability in heart muscle.
What is the inert pair effect in thallium?
The inert pair effect makes thallium’s 6s² electron pair less available for bonding, so Tl⁺ is often more stable than Tl³⁺.