Sulfur (S)

Stable isotopes of sulfur available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Chemical Form
S-32 16 16 31.97207070 94.99% 99.99% Elemental
S-33 16 17 32.9714585 0.75% >99.30% Elemental
S-34 16 18 33.9678669 4.25% >99.00% Elemental
S-36 16 20 35.9670809 0.01% 55.00-99.20% Elemental

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Sulfur (also known as “sulphur”) has been known since ancient times and was referred to in Genesis as “brimstone.” Assyrian texts dated around 700-600 BC refer to it as the “product of the riverside,” where deposits could be found. Its name has origins in the Sanskrit word sulvere and the Latin word sulphurum, both meaning “sulfur.”

Sulfur, particularly in its S8 form, is insoluble in water but dissolves in carbon disulfide, anhydrous liquid ammonia and methylene iodide. It is moderately soluble in benzene, toluene, chloroform and acetone, its solubility increasing with temperature. Solid polymeric sulfur is practically insoluble in all solvents.

Sulfur exists in several allotropic forms: at ordinary temperatures it exists as thermodynamically stable alpha-cyclooctasulfur, which has two other modifications, the beta and the gamma forms. Alpha-cyclooctasulfur, or the alpha sulfur, is a yellow orthorhombic crystalline solid. It has a density of 2.07 g/cm3 at 20 ºC and is stable at ordinary temperatures. Beta-sulfur has pale yellow, opaque, needle-like crystals with a monoclinic structure that is brittle. It is stable between 94.5 ºC and 120 ºC and converts to an orthorhombic form on standing. It has a density of 1.96 g/cm3 and melts at 115.2 ºC. Gamma-sulfur, a pale yellow amorphous solid, is a second monoclinic form of cyclooctasulfur. It has a density of 1.92 g/cm3 and melts at 120 ºC. There are also various other forms of sulfur including cyclohexa-, cyclohepta-, cyclonona-, cyclodeca- and cyclododeca-sulfur.

Elemental sulfur is used for vulcanizing rubber, in making black gunpowder, as a soil conditioner, as a fungicide, preparing a number of metal sulfides, and producing carbon disulfide. It is also used in matches; for bleaching wood pulp, straw, silk and wool; and in the synthesis of many dyes. Pharmaceutical-grade precipitated and sublimed sulfurs are used as scabides and as antiseptics in lotions and ointments.

Properties of Sulfur

Name Sulfur
Symbol S
Atomic number 16
Atomic weight 32.06
Standard state Solid at 298 °K
CAS Registry ID 7704-34-9
Group in periodic table 16 
Group name Chalcogen 
Period in periodic table
Block in periodic table p-block 
Color Lemon yellow
Classification Nonmetallic 
Melting point 115.21 °C
Boiling point 444.72 °C
Thermal conductivity 0.205  W/(m·K)
Electrical resistivity >1023 x 10-8 Ωm
Electronegativity 2.58 
Heat of vaporization 9.8  kJ·mol-1
Heat of fusion 1.73 kJ·mol-1
Density of solid 1.96 g/cm
Electron configuration  [Ne]3s23p4 
Atomic radius  1.03 Å 
Ionic radii

0.37 Å for S4+ (coordination number 6)
and S6+ (coordination number 4);
0.29 Å for hexacoordinated S6+ in crystals

Oxidation states +2, +4, +6

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