Man has known of the yellow non-metallic element sulfur since antiquity. Found in its native state around volcanic vents one of its early uses was as an insecticide. The Greek poet Homer mentioned the insecticidal properties of sulfur in his writings 2800 years ago.
The first chemist to recognize sulfur as an element was Antoine Lavoisier around the year 1777.
The element’s name derives from either the Sanskrit word “sulvere” or the Latin word “sulphurium”. UK English textbooks frequently use the alternative spelling of “sulphur” relating to its Latin root.
Sulfur (symbol S) has the atomic number 16, which puts it in period 3, group 16 (the chalcogen group) of the periodic table. The density of sulfur is 2.067 grams per cubic centimeter, its ionization energy is 10.360 eV and its atomic weight is 32.065.
This brittle, odorless element has three crystal forms or allotropes. Up to the temperature of 96 C (369 K, 204 F) sulfur exists in the stable orthorhombic crystal form above this and up to its melting point of 115.21 °C (388.36 K, 239.38 °F) the element takes on the monoclinic crystal form. On cooling monoclinic sulfur reverts to the orthorhombic crystal form. If the molten element cools rapidly, then sulfur transforms into the third allotrope – amorphous sulfur. Amorphous sulfur is soft and elastic; eventually it reverts to the orthorhombic form. The boiling point of sulfur is 444.6 °C (717.75 K, 832.28 °F).
Most commercially available sulfur comes from underground deposits. The Frasch process, used to recover sulfur from such deposits, involves using pressurized superheated water and steam along with compressed air to melt the sulphur underground and force the liquid element to the surface. The liquid sulfur cools and solidifies in large basins. Other sources of sulfur include as a byproduct from petrochemical refining and other mineral extraction processes. Natural sulfur consists of four stable isotopes sulfur-32 (95.02%), sulfur-34 (4.21%), sulfur-33 (0.75%) and sulfur-35 (0.02%).
Sulfur is biologically essential particularly in the make up of proteins. The amino acids methionine and cysteine contain sulfur bond between these sulfur atoms known as disulfide bridges influence the folding of the polypeptide chain making up the protein. For the protein to function correctly its shape based on such folding must be correct.
Not all compounds that contain sulfur are beneficial to human life. Hydrogen sulfide gas is toxic raised levels killing its victims by paralyzing the respiratory system. However, whole ecosystems thrive based on bacteria that derive their energy from hydrogen sulfide. These ecosystems live around hydrothermal vents in the ocean’s depths known as black smokers.
Reference sources
Los Alamos National Laboratory Chemistry Division
Jefferson Laboratories Science Education website
