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History and Production

Derived from Sanskrit sulvere and Latin sulphurium. Sulfur has been known since prehistoric time. The element was known to Egyptians since sixteenth century BC and Homer refers to its use as fumigant. In Bible, it is known as brimstone in the destruction of Sodom and Gomorrah. It is commercially recovered in the caprock salt domes, produced by the action of bacterial reduction of sedimentary sulfate deposits. Heated water is forced into the wells to melt the sulfur, which is then brought up to the surface. The use of sulfur in black gunpowder was discovered by F.R. Bacon about 1241 though the Chinese and Arabs has produced incendiary mixtures somewhat earlier period of time. Sulfur is also used in the vulcanization of natural rubber, fungicide and fertilizers. It is also very important in sulfuric acid productions, one of the most important manufactured chemical.

Physical Data

Sulfur is a pale yellow, brittle solid insoluble in water but soluble in carbon disulfide (CS2). The allotropy of sulfur is for more complex than any other elements. This is due to the great variety of -S-S- catenation and the ways in which molecules can be arranged within the crystal. The most common and stable is the yellow orthorhombic alpha-form (S8). The monoclinic beta-S8 is less stable which can revert slowly to the alpha form. Another form, the gamma-monoclinic which again, upon standing, reverts slowly to alpha-S8. Sulfur is widely distributed in nature, both in elemental and combined forms. In the latter case, it can exist as H2S in natural gas and crude oil, or as pyrites (FeS2) minerals.

Interatomic distance: 207 pm
Melting point: 115.21°C
Boiling point: 444.60°C
Thermal conductivity/Wm-1K-1: 0.269 (alpha form, 27°C)
Density/kgm-3: 2070 (alpha, 20°C), 1957 (beta, 20°C), 393 (120°C)

Standard Thermodynamic Data (atomic gas, rhombic)

Enthalpy of formation: 277.2 kJ/mol
Gibbs free energy of formation: 236.7 kJ/mol
Entropy: 167.8 J/mol K
Heat capacity: 23.7 J/mol K

Electronic data

Electronic configuration: [Ne] 3s2 3p4
Term symbol: 3P2
Electron affinity: 200.41011 kJ/mol Electronegativity (Pauline): 2.58
Ionization energy (first, second, third): 999.590, 2251.77, 3356.73 kJ/mol

Chemical properties

Sulfur is a very reactive element. It reacts directly with almost all elements, except noble gases. However, sulfur only ignites in air at around 250°C and direct reaction with nitrogen has not been observed. On heating, it combines with halogens except iodine. With many metals it form sulfides.

Test for sulfur:

  1. If a sulfur compound is heated with sodium carbonate in the reducing flame on a charcoal block, it is reduced to sodium sulfide. When the latter is moistened and placed on a piece of silver gives a black stain of silver sulfide.
  2. Oxidation of a sulfur compound with concentrated nitric acid gives sulfuric acid or a sulfate, which can be tested for with barium chloride solution. This test can be used to give quantitative estimate of sulfur.

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