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Name , symbol , atomic number Thallium, Tl, 81
Element category Metals
Group , period , block 13 , 6 , p
Appearance silvery white
CAS number 7440-28-0
EC number 231-138-1
ECHA InfoCard 100.028.307
Mass fraction of the earth's envelope 0.29 ppm
Atomic mass 204.38 (204.382-204.385) u
Atomic radius (calculated) 190 (156) pm
Covalent radius 145 pm
Van der Waals radius 196 pm
Electron configuration [ Xe ] 4 f 14 5 d 10 6 s 2 6p 1
1. Ionization energy 6th.108 287 3 (12) eV 589.36 kJ / mol
2. Ionization energy 20th.4283 (6) eV1 971.03 kJ / mol
3. Ionization energy 29.8520 (6) eV2 880.28 kJ / mol
4. Ionization energy 51.14 (4) eV4 934 kJ / mol
5. Ionization energy 62.6 (4) eV6 040 kJ / mol
Physical state firmly
Crystal structure hexagonal
density 11.85 g / cm 3
Mohs hardness 1.2
magnetism diamagnetic ( Χ m = −3.7 10 −5 )
Melting point 577 K (304 ° C)
boiling point 1733 K (1460 ° C)
Molar volume 17.22 10 −6 m 3 mol −1
Heat of evaporation 162 kJ / mol
Heat of fusion 4.2 kJ mol −1
Speed ​​of sound 818 m s −1 at 293.15 K.
Specific heat capacity 129 J kg −1 K −1
Electric conductivity 6.67 · 10 6 A · V −1 · m −1
Thermal conductivity 46 W m −1 K −1
Oxidation states 1 , 3
Normal potential −0.3363 V (Tl + + e - → Tl)
Electronegativity 1.62 ( Pauling scale )
isotope NH t 1/2 ZA ZE (M eV ) ZP
199 Tl {syn.} 7.42 h ε 1,440 199 ed
200 Tl {syn.} 26.1 h ε 2,456 200 Hg
201 Tl {syn.} 72.912 h ε 0.493 201 ed
202 Tl {syn.} 12.23 d ε 1.364 202 ed
203 Tl 29.524% Stable
204 Tl {syn.} 3.78 a β - 0.764 204 Pb
ε 0.347 204 ed
205 Tl 70.476  % Stable
206 Tl in traces 4.199 min β - 1.533 206 Pb
207 Tl in traces 4.77 min β - 1.423 207 Pb
208 Tl in traces 3.053 min β - 5.001 208 Pb
... ... ... ... ... ...
210 Tl in traces 1.30 min β - (≈ 100%) 5.484 210 Pb
β - n (0.0070%) 0.299 209 Pb
For other isotopes see list of isotopes
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary
06 - Toxic or very toxic 08 - Dangerous to health


H and P phrases H: 330-300-373-413
P: 260-264-284-301 + 310
As far as possible and customary, SI units are used.
Unless otherwise noted, the data given apply to standard conditions .

Thallium is a chemical element with the element symbol Tl and the atomic number 81. In the periodic table it is in the 3rd main group , or the 13th  IUPAC group , the boron group . The soft, gray metal , very similar to lead, is extremely poisonous.


Thallium (from ancient Greek θαλλός thallós 'green branch'; because of its green spectral line at 535 nm) was discovered spectroscopically in England by Sir William Crookes in 1861 in the lead chamber sludge of a sulfuric acid factory based on the characteristic green spectral line. At the same time, the Frenchman Auguste Lamy succeeded in making the metal electrolytically .

Occurrence, limit values

Thallium is not a rare element, but there are very few minerals with a high thallium content : Crookesite (Sweden and Russia), Lorandite (Allchar, Macedonia; USA) and Hutchinsonite . The predominant amount is contained as an accompanying element in clays , soils and granites containing potassium . The natural content is between 0.4 and 6.5 mg / kg. The amount resulting from the smelting of copper , lead , zinc and other sulphidic ores is sufficient to cover demand .

The Federal Institute for Risk Assessment assumes a tolerance value of up to 5 µg / L for drinking water .

The isotope 205 Tl is the final nuclide of the radioactive decay of 209 Bi (half-life 1.9 · 10 19 years) from the Neptunium series .

Extraction and presentation

Thallium is stored under argon because of its sensitivity to air

Metallic thallium is usually obtained by precipitation with zinc. The world production of thallium is 5  tons per year.


Fresh cut surfaces of the soft and malleable metal are high-gloss, after a short time they are covered with a blue-gray oxide film . Thallium (I) hydroxide , which is a very strong base, is formed in moist air and water . It is insoluble in alkaline solutions.

In contrast to the lighter group members, thallium occurs predominantly in the + I oxidation state . This is due to the thermodynamic 6s inert pair effect , as the ionization energy of the 6s electrons is abnormally high. The oxidation states + II and + III are also possible, but are found much less often. Therefore, thallium can be found as a companion in many different minerals.

In many properties, thallium in the + I oxidation state is very similar to the much lighter potassium, which is due not least to the very similar ionic radii. Thallium carbonate is the only heavy metal carbonate that is readily soluble in water. On the other hand, there are also parallels to the corresponding oxidation state of silver (thallium halides are sparingly soluble and sensitive to light).

Thallium compounds show an intense green flame color, in the spectroscope a sharp emission line at 535 nm is characteristic (important in forensics).

Thallium reacts with halogens even at room temperature. The thallium halides that form (with the exception of fluorides) become fluorescent through the uptake of small traces of water at -180 ° C.



Thallium is well absorbed by the body, especially through the gastrointestinal tract or the lungs. Trivalent thallium (Tl 3+ ) is quickly reduced in the body to monovalent thallium (Tl + ) and elemental thallium is oxidized to Tl + , which is distributed very quickly and via the Na + / K + pump from the bloodstream to the cell tissue and organs is transported. Due to the ionic radius of the Tl + , it is from the body, such as potassium - ions K + viewed and transported. High levels of Tl + are found in the kidney and liver, as well as in colon tissue and in certain bones. After surviving poisoning, Tl + can still be found in nails and hair for a long time. Furthermore, Tl + is questionable when excreted from the body. Similar to the amatoxins in the case of tuber agaric poisoning , Tl + is also subject to the so-called enterohepatic cycle . The attempted detoxification via the liver and finally with the bile secretion is prevented by the reabsorption of the Tl + ions in the intestine. Although this route of elimination is quantitatively smaller than that via the kidneys, the kidneys are particularly affected by the damage caused by Tl + . That is why the medically induced detoxification with iron (III) hexacyanoferrate (II) (commonly known as Berlin blue ) begins with excretion via the bile and the intestine (biliary system) . The Tl + released into the duodenum via the bile secretions are chemically bound there or in the intestine by “Berlin blue” and finally excreted in the feces.

No biological function has yet been confirmed for thallium.

safety instructions


Thallium and compounds containing thallium, such as thallium sulfate, are highly toxic and must be handled with great care. Since the general availability of the rat and mouse poison " Zelio " containing thallium sulfate, there has been an increasing number of murder and suicide cases with thallium preparations.

Corroded thallium metal rod

The lethal dose for adult humans is approximately 800 mg. Acute thallium poisoning proceeds in four phases, the first of which is relatively general symptomatically with alternating diarrhea and constipation . In this phase, changes in the hair roots can already be seen, which usually change to the hair loss typical of thallium poisoning on certain parts of the body in different degrees on the 13th day . In the second phase, neurological and psychological changes occur, which are noticeable as excessive pain perception in peripheral parts of the body. The poisoning then culminates in the third phase after the 10th day of admission. There are severe visual disturbances that are caused by the paralysis of the corresponding cranial nerves . The increased cardiac activity ( tachycardia ) is explained by the action of thallium on the stimulation of the sinus node and on the conduction of excitation, which leads to the lethal Tl poisoning due to the resulting cardiac arrhythmias . With the third week of poisoning, the probability of a lethal outcome increases and the late phase (including intestinal perforation) sets in. This usually shows irreversible damage to nerve transmission in the lower parts of the body, disturbed reflexes and muscle wasting . A permanently reduced mental performance can remain, whereby very severe poisoning can lead to severe irreversible brain damage. The body hair develops again after a few months. Smaller amounts lead to chronic poisoning , which can remain undetected for a long time ( Mees nail bands may be observed), but this usually indicates intentional poisoning, as natural absorption of toxic amounts is hardly possible.


During cement production , thallium can accumulate in the form of its volatile halides in the exhaust gas cleaning system.

Animal and vegetable foods usually contain no more than 0.1 mg / kg teaspoon. Nevertheless, mushrooms and some types of cabbage, for example, thallium can accumulate up to 1 mg / kg.

Web links

Wiktionary: Thallium  - explanations of meanings, word origins, synonyms, translations
Commons : Thallium  - album with pictures, videos and audio files

Individual evidence

  1. ^ Harry H. Binder: Lexicon of the chemical elements. S. Hirzel, Stuttgart 1999, ISBN 3-7776-0736-3 .
  2. The values ​​for the properties (info box) are taken from (Thallium) , unless otherwise stated .
  3. The standard value recommended by IUPAC is given, since the isotopic composition of this element can vary locally, the mass range given in brackets results for the mean atomic weight. See: Michael E. Wieser, Tyler B. Coplen: Atomic weights of the elements 2009 (IUPAC Technical Report). In: Pure and Applied Chemistry. 2010, p. 1, doi: 10.1351 / PAC-REP-10-09-14 .
  4. CIAAW, Standard Atomic Weights Revised 2013 .
  5. a b c d e Entry on thallium in Kramida, A., Ralchenko, Yu., Reader, J. and NIST ASD Team (2019): NIST Atomic Spectra Database (ver. 5.7.1) . Ed .: NIST , Gaithersburg, MD. doi : 10.18434 / T4W30F ( ). Retrieved June 13, 2020.
  6. a b c d e Entry on thallium at WebElements, , accessed on June 13, 2020.
  7. Robert C. Weast (Ed.): CRC Handbook of Chemistry and Physics . CRC (Chemical Rubber Publishing Company), Boca Raton 1990, ISBN 0-8493-0470-9 , pp. E-129 to E-145. Values ​​there are based on g / mol and given in cgs units. The value specified here is the SI value calculated from it, without a unit of measure.
  8. a b Yiming Zhang, Julian RG Evans, Shoufeng Yang: Corrected Values ​​for Boiling Points and Enthalpies of Vaporization of Elements in Handbooks. In: Journal of Chemical & Engineering Data . 56, 2011, pp. 328-337, doi: 10.1021 / je1011086 .
  9. a b Entry on thallium in the GESTIS substance database of the IFA , accessed on August 9, 2016(JavaScript required) .
  10. Entry on thallium in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on August 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
  11. ^ Wilhelm Gemoll : Greek-German school and hand dictionary . Munich / Vienna 1965.
  12. a b mm: Geological individual case. In: Local, Kandern. December 20, 2011 (December 4, 2011).
  13. H. Gobrecht, F. Becker: About the luminescence of thallium (I) - and lead (II) halides at low temperatures. In: Journal of Physics. 135, 1953, pp. 553-557, doi: 10.1007 / BF01338819 .
  14. TR: Electricity from waste gas heat. July 30, 2008.
  15. ^ Helmut Schubothe: Poisonings. In: Ludwig Heilmeyer (ed.): Textbook of internal medicine. Springer-Verlag, Berlin / Göttingen / Heidelberg 1955; 2nd edition ibid 1961, pp. 1195-1217, here: pp. 1205 f. ( Thallium poisoning ).
  16. ^ University of Würzburg, approx. 1978-80, two cases of high-grade poisoning, one fatal.
  17. ^ The heartbreaking saga of Zhu Ling ( memento from October 23, 2016 in the Internet Archive ).
  18. C. Thompson, J. Dent, P. Saxby: Effects of thallium poisoning on intellectual function. In: The British journal of psychiatry. Volume 153, 1988, pp. 396-399. PMID 3250680 .
  19. W. Weisweiler, E. Mallonn: thallium - Education, volatilization, enrichment . Iodine and thallium in the cement production process. Dust.