Feb 6 2003
Background
Thallium (T1) was discovered in 1861 by W. Crookes in London, and isolated by C.A. Lamy the following year in Paris.
Occurrence
Thallium is a soft, silvery-grey, reactive metal which is only found as a minor constituent of various minerals (it has an abundance of 0.6 ppm in the earth’s crust), from which the metal is obtained by electrolytic reduction in aqueous solution.
Reactivity
Thallium tarnishes readily in moist air and reacts with steam to form TlOH. It is readily soluble in acids, particularly HNO3, and is highly toxic.
Applications
As a result of its toxicity, Thallium is rarely used, with the exception of the manufacture of special grades of glass.
In the past, Thallium compounds found applications as diverse as rat poisons and hair restorers!
Key Properties
The key properties of Thallium are tabulated below.
Table 1. Key properties
| Atomic Properties |
| Atomic number |
81 |
| Atomic radius - Goldschmidt ( nm ) |
0.171 |
| Atomic weight ( amu ) |
204.383 |
| Crystal structure |
Hexagonal close packed |
| Electronic structure |
Xe 4f14 5d10 6s2 6p1 |
| Photo-electric work function ( eV ) |
3.8 |
| Thermal neutron absorption cross-section ( Barns ) |
3.4 |
| Valences shown |
1, 3 |
| Ionisation Potential |
No. |
eV |
| |
1 |
6.11 |
| |
2 |
20.4 |
| |
3 |
29.8 |
| |
4 |
50.7 |
| Natural Isotope Distribution |
Mass No. |
% |
| |
203 |
29.5 |
| |
205 |
70.5 |
| Electrical Properties |
| Electrical resistivity @ 20 °C ( µOhm.cm ) |
16.6 |
| Temperature coefficient @ 0-100 °C ( K-1 ) |
0.0052 |
| Superconductivity critical temperature ( K ) |
2.38 |
| Thermal emf against Pt (cold 0 °C - hot 100 °C) ( mV ) |
+0.58 |
| Mechanical Properties |
| Material condition |
Polycrystalline |
| Bulk modulus ( GPa ) |
28.5 |
| Hardness – Brinell |
2.0 |
| Poisson’s ratio |
0.45 |
| Tensile modulus ( GPa ) |
7.9 |
| Tensile strength ( MPa ) |
8.96 |
| Physical Properties |
| Boiling point ( °C ) |
1457 |
| Density @ 20 C ( g.cm-3 ) |
11.85 |
| Melting point ( °C ) |
303.5 |
| Thermal Properties |
| Coefficient of thermal expansion @ 0-100 °C ( x10-6 K-1 ) |
30.0 |
| Latent heat of evaporation ( J.g-1 ) |
813 |
| Latent heat of fusion ( J.g-1 ) |
21.0 |
| Specific heat @ 25 °C ( J.K-1.kg-1 ) |
128 |
| Thermal conductivity @ 0-100 °C ( W.m-1.K-1 ) |
46.1 |
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