Antimony

Antimony is a chemical element; it has symbol Sb (from Latin stibium) and atomic number 51. A lustrous grey metal or metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb₂S₃). Antimony compounds have been known since ancient times and were powdered for use as medicine and cosmetics, often known by the Arabic name kohl. The earliest known description of this metalloid in the West was written in 1540 by Vannoccio Biringuccio.

China is the largest producer of antimony and its compounds, with most production coming from the Xikuangshan Mine in Hunan. The industrial methods for refining antimony from stibnite are roasting followed by reduction with carbon, or direct reduction of stibnite with iron.

The most common applications for metallic antimony are in alloys with lead and tin, which have improved properties for solders, bullets, and plain bearings. It improves the rigidity of lead-alloy plates in lead–acid batteries. Antimony trioxide is a prominent additive for halogen-containing flame retardants. Antimony is used as a dopant in semiconductor devices.

Antimony is a member of group 15 of the periodic table. As one of the elements called pnictogens, it has an electronegativity of 2.05. In accordance with periodic trends, it is more electronegative than tin or bismuth, and less electronegative than tellurium or arsenic. As a metalloid, it has a Mohs scale hardness of 3.

Antimony is a silvery, lustrous gray solid that is stable in air at room temperature. If heated, it reacts with oxygen to produce antimony trioxide,Sb₂O₃. Antimony is attacked by oxidizing acids.

The stable allotrope of antimony crystallises in a trigonal cell, isomorphic with bismuth and the gray allotrope of arsenic.

A yellow allotrope of antimony, assumed to be analogous to yellow arsenice, forms by oxidation of stibine (SbH₃) with air or oxygen at −90 °C. At ambient temperatures and in ambient light, it transforms into the more stable black allotrope. A rare explosive form of antimony can be formed from the electrolysis of antimony trichloride, but it always contains appreciable chlorine and is not really an antimony allotrope. When scratched with a sharp implement, an exothermic reaction occurs and white fumes are given off as metallic antimony forms; when rubbed with a pestle in a mortar, a strong detonation occurs.

Elemental antimony adopts a layered structure (space group R3m No. 166) whose layers consist of fused, ruffled, six-membered rings. The nearest and next-nearest neighbors form an irregular octahedral complex, with the three atoms in each double layer slightly closer than the three atoms in the next. This relatively close packing leads to a high density of 6.697 g/cm³, but the weak bonding between the layers leads to the low hardness and brittleness of antimony.