Sulphur
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Sulphur (aka sulfur) is a chemical element, typically found as a yellowish crystalline solid in its elemental form. It has the chemical symbol S, atomic number (number of protons) Z = 16, and a standard atomic weight of 32.065 g/mol.
Sulphur is widely used in the manufacture of sulphuric acid (H2SO4} as well as various fertilisers. The vast majority of the 66,000,000 metric tons of sulphur produced worldwide in 2006 was by-product sulphur recovered from petroleum refining and natural gas processing plants by the Claus process.[1]
Characteristics
At room temperature, sulphur is a soft, bright-yellow solid. Elemental sulphur has only a faint odour, similar to that of matches.
Sulphur burns with a blue flame that emits sulphur dioxide, notable for its peculiar suffocating odour due to dissolving in the mucosa to form dilute sulphurous acid.
Sulphur itself is insoluble in water, but soluble in carbon disulfide and to a lesser extent in other non-polar organic solvents such as benzene and toluene.
Common oxidation states of sulphur include −2, +2, +4 and +6. Sulphur forms stable compounds with all elements except the noble gases. Sulphur in the solid state ordinarily exists as cyclic crown-shaped S8 molecules.
The crystallography of sulphur is complex. Depending on the specific conditions, the sulphur allotropes form several distinct crystal structures, with rhombic and monoclinic S8 best known.
A noteworthy property of sulphur is that its viscosity in its molten state, unlike most other liquids, increases above temperatures of 200 °C due to the formation of polymers. The molten sulphur assumes a dark red colour above this temperature. At higher temperatures, however, the viscosity is decreased as depolymerization occurs.
Amorphous or "plastic" sulphur can be produced through the rapid cooling of molten sulphur. X-ray crystallography studies show that the amorphous form may have a helical structure with eight atoms per turn. This form is metastable at room temperature and gradually reverts back to crystalline form. This process happens within a matter of hours to days but can be rapidly catalysed.