Elemental arsenic occurs in two solid modifications: yellow, and grey or metallic, with specific gravities of 1.97, and 5.73, respectively. The element is a steel grey, very brittle, crystalline, semimetallic (metalloid) solid. It tarnishes in air, and when heated rapidly oxidises to arsenous oxide which has a garlic odour.
Arsenic and its compounds are poisonous as any reader of "who-done-it" books knows. Upon heating arsenic and some minerals containing arsenic, it sublimes (transfers from the solid to the gaseous state, without passing through the liquid state).
This sample is fromThe Elements Collection, an attractive and safely packaged collection of the 92 naturally occurring elements that is available for sale.
Arsenic, despite its poisonous reputation, may be a necessary ultratrace element for humans. It is a necessary ultratrace element for red algae, chickens, rats, goats, and pigs. A deficiency results in inhibited growth.
Isolation: it is not usually necessary to make arsenic in the laboratory as it is commercially available. Arsenic is found in nature in a number of minerals including realgar (As4S4), orpiment (As2S3), arsenolite (As2O3), and iron minerals such as arsenopyrite (FeAsS) and loellingite (FeAs2). Arsenic is made on an industrial scale by heating appropriate minerals in the absence of air. The arsenic is condensed out as a solid.
Density of solid: 5727 kg m-3
Molar volume: 12.95 cm3
Thermal conductivity: 50 W m‑1 K‑1
Melting point: 1090 [817 °C (1503 °F)] (under pressure) K
Boiling point: 887 [614 °C (1137 °F)] (sublimes) K
Enthalpy of fusion: 20.5 kJ mol-1
Atomic radius (empirical): 115 pm
Molecular single bond covalent radius: 121 (coordination number 3) ppm
van der Waals radius: 188 ppm
Pauling electronegativity: 2.18 (Pauling units)
Allred Rochow electronegativity: 2.20 (Pauling units)
Mulliken-Jaffe electronegativity: 2.26 (20% s orbital)
First ionisation energy: 944.45 kJ mol‑1
Second ionisation energy: 1793.58 kJ mol‑1
Third ionisation energy: 2735.3 kJ mol‑1
Universe: 8 ppb by weight
Crustal rocks: 2100 ppb by weight
Human: 50 ppb by weight
