Thallium

Thallium, ₈₁Tl
Thallium
Pronunciation	/ˈθæliəm/ (THAL-ee-əm)
Appearance	silvery white
Standard atomic weight Ar°(Tl)
	[204.382, 204.385]; 204.38±0.01 (abridged);
Thallium in the periodic table
	mercury ← thallium → lead
Atomic number (Z)	81
Group	group 13 (boron group)
Period	period 6
Block	p-block
Electron configuration	[Xe] 4f14 5d10 6s2 6p1
Electrons per shell	2, 8, 18, 32, 18, 3
Physical properties
Phase at STP	solid
Melting point	577 K (304 °C, 579 °F)
Boiling point	1746 K (1473 °C, 2683 °F)
Density (at 20° C)	11.873 g/cm3
when liquid (at m.p.)	11.22 g/cm3
Heat of fusion	4.14 kJ/mol
Heat of vaporization	165 kJ/mol
Molar heat capacity	26.32 J/(mol·K)
Atomic properties
Oxidation states	common: +1, +3; −5, −2,? −1,? +2?
Electronegativity	Pauling scale: 1.62
Ionization energies	1st: 589.4 kJ/mol ; 2nd: 1971 kJ/mol ; 3rd: 2878 kJ/mol ; ;
Atomic radius	empirical: 170 pm
Covalent radius	145±7 pm
Van der Waals radius	196 pm
	Spectral lines of thallium
Other properties
Natural occurrence	primordial
Crystal structure	hexagonal close-packed (hcp) (hP2)
Lattice constants	a = 345.66 pm; c = 552.52 pm (at 20 °C)
Thermal expansion	29.9 µm/(m⋅K) (at 25 °C)
Thermal conductivity	46.1 W/(m⋅K)
Electrical resistivity	0.18 µΩ⋅m (at 20 °C)
Magnetic ordering	diamagnetic
Molar magnetic susceptibility	−50.9×10−6 cm3/mol (298 K)
Young's modulus	8 GPa
Shear modulus	2.8 GPa
Bulk modulus	43 GPa
Speed of sound thin rod	818 m/s (at 20 °C)
Poisson ratio	0.45
Mohs hardness	1.2
Brinell hardness	26.5–44.7 MPa
CAS Number	7440-28-0
History
Naming	after Greek thallos, green shoot or twig
Discovery	William Crookes (1861)
First isolation	Claude-Auguste Lamy (1862)
Isotopes of thallium v; e;
ε + β+	204Hg
	Category: Thallium; view; talk; edit; \| references

Thallium is a chemical element; it has symbol Tl and atomic number 81. It is a silvery-white post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Chemists William Crookes and Claude-Auguste Lamy discovered thallium independently in 1861, in residues of sulfuric acid production. Both used the newly developed method of flame spectroscopy, in which thallium produces a notable green spectral line. Thallium, from Greek θαλλός, thallós, meaning "green shoot" or "twig", was named by Crookes. It was isolated by both Lamy and Crookes in 1862; Lamy by electrolysis and Crookes by precipitation and melting of the resultant powder. Crookes exhibited it as a powder precipitated by zinc at the international exhibition, which opened on 1 May that year.^[8]

Thallium tends to form the +3 and +1 oxidation states. The +3 state resembles that of the other elements in group 13 (boron, aluminium, gallium, indium). However, the +1 state, which is far more prominent in thallium than the elements above it, recalls the chemistry of alkali metals and thallium(I) ions are found geologically mostly in potassium-based ores and (when ingested) are handled in many ways like potassium ions (K⁺) by ion pumps in living cells.

Commercially, thallium is produced not from potassium ores, but as a byproduct from refining of heavy-metal sulfide ores. Approximately 65% of thallium production is used in the electronics industry and the remainder is used in the pharmaceutical industry and in glass manufacturing.^[9] It is also used in infrared detectors. The radioisotope thallium-201 (as the soluble chloride TlCl) is used in small amounts as an agent in a nuclear medicine scan, during one type of nuclear cardiac stress test.

Soluble thallium salts (many of which are nearly tasteless) are highly toxic and they were historically used in rat poisons and insecticides. Because of their nonselective toxicity, use of these compounds has been restricted or banned in many countries. Thallium poisoning usually results in hair loss. Because of its historic popularity as a murder weapon, thallium has gained notoriety as "the poisoner's poison" and "inheritance powder" (alongside arsenic).^[10]

^ "Standard Atomic Weights: Thallium". CIAAW. 2009.
^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
^ ^a ^b Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.
^ Dong, Z.-C.; Corbett, J. D. (1996). "Na₂₃K₉Tl_15.3: An Unusual Zintl Compound Containing Apparent Tl₅⁷⁻, Tl₄⁸⁻, Tl₃⁷⁻, and Tl⁵⁻ Anions". Inorganic Chemistry. 35 (11): 3107–12. doi:10.1021/ic960014z. PMID 11666505.
^ Lide, D. R., ed. (2005). "Magnetic susceptibility of the elements and inorganic compounds". CRC Handbook of Chemistry and Physics (PDF) (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.
^ Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
^ The Mining and Smelting Magazine Archived 2021-02-24 at the Wayback Machine. Ed. Henry Curwen Salmon. Vol. iv, July–Dec 1963, p. 87.
^ Cite error: The named reference sl2001 was invoked but never defined (see the help page).
^ Hasan, Heather (2009). The Boron Elements: Boron, Aluminum, Gallium, Indium, Thallium. Rosen Publishing Group. p. 14. ISBN 978-1-4358-5333-1.

[1] "Standard Atomic Weights: Thallium". CIAAW. 2009.

[CIAAW2021-2] Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.

[Arblaster_2018-3] Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.

[4] Dong, Z.-C.; Corbett, J. D. (1996). "Na₂₃K₉Tl_15.3: An Unusual Zintl Compound Containing Apparent Tl₅⁷⁻, Tl₄⁸⁻, Tl₃⁷⁻, and Tl⁵⁻ Anions". Inorganic Chemistry. 35 (11): 3107–12. doi:10.1021/ic960014z. PMID 11666505.

[5] Lide, D. R., ed. (2005). "Magnetic susceptibility of the elements and inorganic compounds". CRC Handbook of Chemistry and Physics (PDF) (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.

[6] Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.

[NUBASE2020-7] Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.

[8] The Mining and Smelting Magazine Archived 2021-02-24 at the Wayback Machine. Ed. Henry Curwen Salmon. Vol. iv, July–Dec 1963, p. 87.

[sl2001-9] Cite error: The named reference sl2001 was invoked but never defined (see the help page).

[10] Hasan, Heather (2009). The Boron Elements: Boron, Aluminum, Gallium, Indium, Thallium. Rosen Publishing Group. p. 14. ISBN 978-1-4358-5333-1.

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