Feb 11 2003
Discovered in the 13th. century by Albertus Magnus (although believed to have been used much earlier as an alloying addition to bronze to provide a lustrous finish).
Arsenic (As) is found in several allotropic forms and has both metallic and non-metallic properties. The grey metallic allotrope is a brittle, crystalline solid which tarnishes readily in air and burns in oxygen. Arsenic is resistant to attack by dilute acids and alkalis, but will react with hot acids and molten NaOH.
Occurrence
Arsenic is poisonous (it is thought to have been responsible for the death of Napoleon) and occurs both free and combined in many minerals (Arsenic has an abundance within the earth's crust of 1.5 ppm).
Production
The non-metallic allotropes include yellow arsenic (may be formed by rapid condensation of Arsenic vapour in an inert atmosphere) and black arsenic (may be formed by slow condensation of the vapour in an inert atmosphere).
Applications
Applications for grey Arsenic include its use as an alloying element, its use in the manufacture of certain types of glass and as a donor impurity in germanium semiconductor devices.
Key Properties
The key properties of Arsenic are tabulated below.
Table 1. Key properties
| Atomic Properties |
| Atomic number |
33 |
| Atomic radius - Goldschmidt ( nm ) |
0.125 |
| Atomic weight ( amu ) |
74.9216 |
| Crystal structure |
Rhombohedral |
| Electronic structure |
Ar 3d10 4s2 4p3 |
| Photo-electric work function ( eV ) |
5.1 |
| Thermal neutron absorption cross-section ( Barns ) |
4.3 |
| Valences shown |
-3, 0, 3, 5 |
| Ionisation Potential |
No. |
eV |
| |
1 |
9.81 |
| |
2 |
18.6 |
| |
3 |
28.4 |
| |
4 |
50.1 |
| |
5 |
62.6 |
| |
6 |
128 |
| Natural Isotope Distribution |
Mass No. |
% |
| |
75 |
100 |
| Electrical Properties |
| Electrical resistivity @ 20 °C ( µOhm.cm ) |
33.3 |
| Mechanical Properties |
| Material condition |
Polycrystalline |
| Bulk modulus ( GPa ) |
22.0 |
| Hardness - Vickers |
57-69 |
| Physical Properties |
| Boiling point (°C ) |
616 |
| Density @ 20 °C ( g.cm-3 ) |
5.73 |
| Melting point (°C ) |
Sublimes >300 |
| Thermal Properties |
| Coefficient of thermal expansion @ 0-100 °C ( x10-6 K-1 ) |
5.6 |
| Latent heat of fusion ( J.g-1 ) |
370 |
| Specific heat @ 25 °C ( J.K-1.kg-1 ) |
328 |
| Thermal conductivity @ 0-100 °C ( W.m-1.K-1 ) |
50.2 |
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