Thallium

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81 mercury ← thallium → lead
In

Tl

Uut
Periodic Table - Extended Periodic Table
General
Name, Symbol, Number thallium, Tl, 81
Element category poor metals
Group, Period, Block 13, 6, p
Appearance silvery white
Standard atomic weight 204.3833(2)  g·mol−1
Electron configuration [Xe] 4f14 5d10 6s2 6p1
Electrons per shell 2, 8, 18, 32, 18, 3
Physical properties
Phase solid
Density (near r.t.) 11.85  g·cm−3
Liquid density at m.p. 11.22  g·cm−3
Melting point 577 K
(304 °C, 579 °F)
Boiling point 1746 K
(1473 °C, 2683 °F)
Heat of fusion 4.14  kJ·mol−1
Heat of vaporization 165  kJ·mol−1
Specific heat capacity (25 °C) 26.32  J·mol−1·K−1
Vapor pressure
P(Pa) 1 10 100 1 k 10 k 100 k
at T(K) 882 977 1097 1252 1461 1758
Atomic properties
Crystal structure hexagonal
Oxidation states 3, 1
(mildly basic oxide)
Electronegativity 1.62 (Pauling scale)
Ionization energies 1st: 589.4 kJ/mol
2nd: 1971 kJ/mol
3rd: 2878 kJ/mol
Atomic radius 190  pm
Atomic radius (calc.) 156  pm
Covalent radius 148  pm
Van der Waals radius 196 pm
Miscellaneous
Magnetic ordering  ???
Electrical resistivity (20 °C) 0.18 µ Ω·m
Thermal conductivity (300 K) 46.1  W·m−1·K−1
Thermal expansion (25 °C) 29.9  µm·m−1·K−1
Speed of sound (thin rod) (20 °C) 818 m/s
Young's modulus 8  GPa
Shear modulus 2.8  GPa
Bulk modulus 43  GPa
Poisson ratio 0.45
Mohs hardness 1.2
Brinell hardness 26.4  MPa
CAS registry number 7440-28-0
Most-stable isotopes
Main article: Isotopes of thallium
iso NA half-life DM DE (MeV) DP
203Tl 29.524% 203Tl is stable with 122 neutrons
204Tl syn 119 Ms
(3.78 y)
β- 0.764 204Pb
ε 0.347 204Hg
205Tl 70.476% 205Tl is stable with 124 neutrons
References

Thallium (pronounced /ˈθæliəm/) is a chemical element with the symbol Tl and atomic number 81. This soft gray malleable poor metal resembles tin but discolors when exposed to air. Approximately 60-70% of thallium production is used in the electronics industry, and the rest is used in the pharmaceutical industry and in glass manufacturing. It is also used in infrared detectors. Thallium is highly toxic and is used in rat poisons and insecticides, and its use has been cut back or eliminated in many countries. It is used in murders and has the nicknames "The Poisoner's Poison" and "Inheritance powder" (alongside arsenic).

Contents

Characteristics

1 gram of Thallium 1 gram of Thallium

Thallium is very soft and malleable and can be cut with a knife. It has a metallic luster, but when exposed to air, it quickly tarnishes with a bluish-grey tinge that resembles lead. (It is preserved by keeping it under oil). A heavy layer of oxide builds up on thallium if left in air. In the presence of water, thallium hydroxide is formed.

Occurrence and production

Thallium occurs naturally in the minerals crookesite, lorandite, hutchinsonite, and pyrite.

Thallium metal is obtained as a by-product in the production of sulfuric acid by roasting of pyrite, and also in the smelting of lead and zinc ores.

Applications

The odorless and tasteless thallium sulfate was once widely used as rat poison and ant killer. Since 1975, this use in the United States and many other countries is prohibited due to safety concerns. Other uses:

In addition, research activity with thallium is ongoing to develop high-temperature superconducting materials for such applications as magnetic resonance imaging, storage of magnetic energy, magnetic propulsion, and electric power generation and transmission.

History

Thallium (Greek θαλλός, thallos, meaning "a green shoot or twig") was discovered by Sir William Crookes in 1861 in England while he was making spectroscopic determinations for tellurium on residues from a sulfuric acid plant. The name comes from Thallium's bright green spectral emission lines. In 1862 Crookes and Claude-Auguste Lamy isolated the metal independently of each other.

Occurrence

Although the metal is reasonably abundant in the Earth's crust at a concentration estimated to be about 0.7 mg/kg, mostly in association with potassium minerals in clays, soils, and granites, it is not generally considered to be commercially recoverable from those forms. The major source of commercial thallium is the trace amounts found in copper, lead, zinc, and other sulfide ores.

Thallium is found in the minerals crookesite TlCu7Se4, hutchinsonite TlPbAs5S9, and lorandite TlAsS2. It also occurs as trace in pyrite and extracted as a by-product of roasting this ore for sulfuric acid production. The metal can be obtained from the smelting of lead and zinc rich ores. Manganese nodules found on the ocean floor also contain thallium, but nodule extraction is prohibitively expensive and potentially environmentally destructive. In addition, several other thallium minerals, containing 16% to 60% thallium, occur in nature as sulfide or selenide complexes with antimony, arsenic, copper, lead, and silver, but are rare, and have no commercial importance as sources of this element. See also: Category:Thallium minerals.

Isotopes

Main article: isotopes of thallium

Thallium has 25 isotopes which have atomic masses that range from 184 to 210. 203Tl and 205Tl are the only stable isotopes, and 204Tl is the most stable radioisotope, with a half-life of 3.78 years.

202Tl (half life 12.23 days) can be made in a cyclotron, while 204Tl (half life 3.78 years) is made by the neutron activation of stable thallium in a nuclear reactor.

Compounds

Fluorides: TlF, TlF3
Chlorides: TlCl, TlCl2, TlCl3
Bromides: TlBr, Tl2Br4
Iodides: TlI, TlI3
Hydrides: none listed
Oxides: Tl2O, Tl2O3
Sulfides: Tl2S
Selenides: Tl2Se
Tellurides: none listed
Nitrides: none listed

Toxicity

Thallium and its compounds are very toxic, and should be handled with great care[1]. Contact with skin is dangerous, and adequate ventilation should be provided when melting this metal[2].Thallium(I) compounds have a high aqueous solubility and are readily absorbed through the skin. Exposure to them should not exceed 0.1 mg per m² of skin in an 8-hour time-weighted average (40-hour work week). Thallium is a suspected human carcinogen.

Part of the reason for thallium's high toxicity is that, when present in aqueous solution as the univalent thallium(I) ion (Tl+), it exhibits some similarities with essential alkali metal cations, particularly potassium (as the atomic radius is almost identical). It can thus enter the body via potassium uptake pathways. However, other aspects of thallium's chemistry are very different from that of the alkali metals (e.g., its high affinity for sulfur ligands due to the presence of empty d-orbitals), and so this substitution disrupts many cellular processes (for instance, thallium may attack sulfur-containing proteins such as cysteine residues and ferredoxins).

Thallium's toxicity has led to its use (now discontinued in many countries) as a rat and ant poison.

Among the distinctive effects of thallium poisoning are loss of hair (which led it to its initial use as a depilatory before its toxicity was properly appreciated) and damage to peripheral nerves (victims may experience a sensation of walking on hot coals). Thallium was once an effective murder weapon before its effects became understood, and an antidote (prussian blue) discovered.

Treatment and internal decontamination

One of the main methods of removing thallium (both radioactive and normal) from humans is to use Prussian blue, which is a solid ion exchange material which absorbs thallium and releases potassium. The prussian blue is fed by mouth to the person, and it passes through their digestive system and comes out in the stool.

Famous uses as a poison

Corroded thallium rod Corroded thallium rod

In fiction