|Name, symbol||Thallium, Tl|
|Appearance||Silvery white metal|
|Thallium in the periodic table|
|Standard atomic weight (Ar)||204.38|
|Group, block||13; p-block|
|Electron configuration||[Xe] 4f14 5d10 6s2 6p1|
|2, 8, 18, 32, 18, 3|
|Melting point||577 K (304 °C, 579 °F)|
|Boiling point||1746 K (1473 °C, 2683 °F)|
|Density near r.t.||11.85 g/cm3|
|when liquid, at||11.22 g/cm3|
|Heat of fusion||4.14 kJ/mol|
|Heat of||165 kJ/mol|
|Molar heat capacity||26.32 J/(mol·K)|
|Oxidation states||3, 2, 1, −1, −2, −5 (a mildly basic oxide)|
|Electronegativity||Pauling scale: 1.62|
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|
|Crystal structure||hexagonal close-packed (hcp)|
|Speed of sound thin rod||818 m/s (at 20 °C)|
|Thermal expansion||29.9 µm/(m·K) (at 25 °C)|
|Thermal conductivity||46.1 W/(m·K)|
|Electrical resistivity||0.18 Ω·m (at 20 °C)|
|Young's modulus||8 GPa|
|Shear modulus||2.8 GPa|
|Bulk modulus||43 GPa|
|Brinell hardness||26.5–44.7 MPa|
|CAS Registry Number||7440-28-0|
|Discovery||William Crookes (1861)|
|First isolation||Claude-Auguste Lamy (1862)|
Thallium is a chemical element with symbol Tl and atomic number 81. It is a toxic element with few common applications.
Thallium quickly oxidizes in air to form a layer of thallium oxide. Acids, such as sulfuric and nitric acids, will dissolve thallium forming their respective salts. However, thallium is largely unaffected by hydrochloric acid, due to an insoluble layer of thallium(I) chloride.
While thallium displays 3+ oxidation state, like the elements from its group (aluminium, gallium) the most common oxidation state encountered for thallium is the +1 oxidation state. This state gives thallium several properties similar to that of alkali metals.
Thallium is extremely soft, malleable metal which can be cut cut with a knife at room temperature. It has a metallic luster that, when exposed to air, quickly tarnishes to a bluish-gray tinge, resembling lead. Thallium melts at 304 °C and boils at 1473 °C. It is quite dense, having a density of 11.85 g/cm3, slightly denser than lead.
Thallium is sold by various chemical suppliers, though it may not be cheap due to its hazardous nature. In many places the sale of thallium metal and compounds is restricted.
Certain rat poisons may contain thallium.
Thallium can be extracted from its compounds by reducing them, however this process is very dangerous, as thallium is extremely toxic, fact accentuated by its low melting point.
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Thallium is extremely toxic and most of its compounds pose severe toxicity and is also a potent carcinogenic. Most thallium salts are nearly tasteless, which makes accidental poisoning very easy. People can be exposed to thallium by breathing it in, skin absorption, swallowing it, or eye contact. One of the most distinct effects of thallium poisoning is hair loss and fingernail peeling (Mees' lines).
Thallium is best stored in ampoules or under a liquid, like mineral oil.
Thallium and its compounds must be taken to special disposal facilities.