Sulfur or sulphur (see spelling differences) is a chemical element with symbol S and atomic number 16. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow crystalline solid at room temperature. Chemically, sulfur reacts with all elements except for nitrogen and the noble gases.
Elemental sulfur occurs naturally as the element (native sulfur), but most commonly occurs in combined forms as sulfide and sulfate minerals. Being abundant in native form, sulfur was known in ancient times, being mentioned for its uses in ancient India, ancient Greece, China, and Egypt. Sulfur is referred to in the Bible as ''brimstone''.〔 Today, almost all elemental sulfur is produced as a byproduct of removing sulfur-containing contaminants from natural gas and petroleum. The element's largest commercial use (after mostly being converted to sulfuric acid) is to produce sulfate and phosphate fertilizers, because of the relatively high requirement of plants for sulfur and phosphorus. Sulfuric acid is also a primary industrial chemical outside fertilizer manufacture. Other uses for the element are in matches, insecticides and fungicides. Many sulfur compounds are odoriferous, and the smell of odorized natural gas, skunk scent, grapefruit, and garlic is due to organosulfur compounds. Hydrogen sulfide imparts the characteristic odor to rotting eggs and other biological processes.
Sulfur is an essential element for all life, but almost always in the form of organosulfur compounds or metal sulfides. Three amino acids (cysteine, cystine, and methionine) and two vitamins (biotin and thiamine) are organosulfur compounds. Many cofactors also contain sulfur including glutathione and thioredoxin and iron-sulfur proteins. Disulfides, S-S bonds, confer mechanical strength and insolubility of the protein keratin, found in outer skin, hair, and feathers. Elemental sulfur is not common in higher forms of life, but is both a product and an oxidant for various bacteria.
==Spelling and etymology==
''Sulfur'' is derived from the Latin word ''sulpur'', which was Hellenized to ''sulphur''. The spelling ''sulfur'' appears toward the end of the Classical period. (The true Greek word for sulfur, ''θεῖον'', is the source of the international chemical prefix ''thio-''.) In 12th-century Anglo-French, it was ''sulfre''; in the 14th century the Latin ''ph'' was restored, for ''sulphre''; and by the 15th century the full Latin spelling was restored, for ''sulfur, sulphur''. The parallel ''f~ph'' spellings continued in Britain until the 19th century, when the word was standardized as ''sulphur''. ''Sulfur'' was the form chosen in the United States, whereas Canada uses both. However, the IUPAC adopted the spelling ''sulfur'' in 1990, as did the Nomenclature Committee of the Royal Society of Chemistry in 1992, restoring the spelling ''sulfur'' to Britain. The Oxford Dictionaries note that "in chemistry ... the -f- spelling is now the standard form in all related words in the field in both British and US contexts."〔(【引用サイトリンク】title= Ask Oxford )〕
The late Latin form also continues in the Romance languages: French ''soufre'', Italian ''zolfo'' (from ''solfo''), Spanish ''azufre'' (from ''açufre'', from earlier ''çufre''), Portuguese ''enxofre'' (from ''xofre''). The Spanish and Portuguese forms are prefixed with the Arabic article, despite not being Arabic words.〔 The root has been traced back to reconstructed proto-Indo-European (genitive ), a nominal derivative of 'to burn', a lineage also preserved in the Germanic languages, where it is found for example as modern German ''Schwefel'', Dutch ''zwavel'', and Swedish ''svavel'', and as Old English ''swefl''.〔Mallory & Adams (2006) ''The Oxford introduction to Proto-Indo-European and the Proto-Indo-European world'', Oxford University Press〕
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