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Sulfide

Sulfide

In chemistry, a sulfide (sulphide in British) is a chemical compound or combination of sulfur with an oxidation number of -2, with another chemical element or a radical thereof. Some covalent sulfur compounds, such as carbon disulfide (CS₂) and hydrogen sulfide (H₂S), are also considered to be sulfides. Thioethers are organic compounds of the form
R-S-R' (where R and R' are organic radicals), which are also referred to as sulfides or (if R,R' are alkyl) dialkyl sulfides. The sulfide ion is S^2-, an anion with a -2 charge on it. In aqueous solutions, sulfide ions are only present in large concentrations at alkaline pH (high pH), because at lower pH, H⁺ will combine with sulfide ions to form HS^- or H₂S. HS^- is the hydrogen sulfide ion, hydrosulfide ion, or sulfhydryl ion. H₂S is hydrogen sulfide, a water-soluble gas which is a weak diprotic acid. Ionically bonded sulfides can be thought of as salts of the acid hydrogen sulfide. Many inorganic sulfide salts are not very water-soluble and many have very low solubility in water. If an -SH functional group is covalently bonded to another atom or group such as an organic radical R in a thiol, then it is typically called a sulfhydryl group. Such sulfhydryl groups can also be weakly acidic, and can give up an H⁺ to form a substituted sulfide ion. For example, ethyl hydrosulfide, C₂H₅SH, can give up an H⁺ to form an ethyl sulfide ion,C₂H₅S^-, although often other names are used for such compounds; see Thiol. The sulfur in sulfides (or in the sulfide functional groups) is in its lowest oxidation state. In sulfides, this sulfur can often be oxidized to a higher oxidation state. For example, the thioether dimethyl sulfide (CH₃-S-CH₃) could be oxidized to dimethyl sulfoxide (CH₃-SO-CH₃), which could in turn be oxidized to dimethyl sulfone (CH₃-SO₂-CH₃). Disulfides are similar compounds having two sulfur atoms covalently bonded together and covalently or ionically bonded to the rest of the molecule or compound. Hydrogen sulfide gas has the odor of rotten eggs, and is also highly toxic. It is formed biologically in the sediments of swamps and in the treatment of sewage sludge by anaerobic digestion of sulfur containing proteins, or bacterial reduction of sulfates. It also occurs in some natural gas and in the emissions of some volcanoes, and as a byproduct of some industrial processes.

Examples

- hydrogen sulfide (H₂S)
- sodium sulfide (Na₂S)
- carbon disulfide (CS₂)
- tetraphosphorus decasulfide (P₄S₁₀)

Uses

- Cadmium disulfide (CdS₂) can be used in photocells.
- Calcium polysulfide ("lime sulfur") is a traditional fungicide in gardening.
- Carbon disulfide (CS₂) is sometimes used as a solvent in industrial chemistry.
- Lead sulfide (PbS) is used in infra-red sensors.
- Silver sulfide (Ag₂S) is formed on silver electrical contacts operating in an atmosphere rich in Hydrogen sulfide.
- Sodium sulfide (Na₂S) is an important industrial chemical, used in manufacture of kraft paper, dyes, leather tanning, crude petroleum processing, treatment of heavy metal pollution, and others.
- Zinc sulfide (ZnS) is used for lenses and other optical devices in the infrared part of the spectrum.
- Zinc sulfide with a trace of copper is used for photoluminescent strips for emergency lighting and luminous watch dials.
- Several metal sulfides are used as pigments in art, although their use has declined somewhat due to their toxicity. Sulfide pigments include cadmium, mercury, and arsenic.
- Polyphenylene sulfide is a polymer material commonly called Sulfar. Its repeating units are bonded together by sulfide (thioether) linkages.

Natural occurrence

Many important metal ores are sulfides. Significant sulfide minerals include:
- arsenopyrite (arsenic and iron)
- argentite (silver)
- chalcopyrite (iron and copper)
- cinnabar (mercury)
- galena (lead)
- molybdenite (molybdenum)
- pentlandite (nickel)
- pyrite (iron)
- realgar (arsenic)
- sphalerite (zinc) and
- stibnite (antimony).

Safety

Many sulfides are significantly toxic by inhalation or injection, especially if the metal ion is toxic. Additionally many sulfides, when exposed to a strong mineral acid, will release toxic hydrogen sulfide - and this includes your stomach acids! Also, many sulfides, particularly organic sulfides are somewhat flammable, and a few are highly flammable. When a sulfide burns, the fumes usually include toxic sulfur dioxide (SO₂) gas.

Chemistry

Chemistry (derived from the Arabic word kimia, alchemy, where al is Arabic for the) is the science of matter that deals with the composition, structure, and properties of substances and with the transformations that they undergo. In the study of matter, chemistry also investigates its interactions with energy and itself (see physics, biology). Because of the diversity of matter, which is mostly composed of different combinations of atoms, chemists often study how atoms of different chemical elements interact to form molecules and how molecules interact with each other. molecules

Introduction

Chemistry is a large field encompassing many subdisciplines that often overlap with significant portions of other sciences. The fundamental component of chemistry is that it involves matter in some way (this explains its broad reach). It may involve the interaction of matter with non-material phenomena such as energy. More central to chemistry is the interaction of matter with other matter such as in the classic chemical reaction where chemical bonds are broken and made, forming new molecules. Matter, such as the chair you are sitting on or the air you breathe, is known today to consist of molecules. Each molecule consists of small bits of matter known as atoms that are connected together through chemical bonds. Each atom consists of smaller bits of matter known as subatomic particles. The structure of the world we commonly experience and the properties of the matter we commonly interact with are determined by the nature of this matter on the chemical level. Steel is hard because of how the atoms are bound together. Wood will burn because it can react with oxygen in a chemical reaction. Water is a liquid at room temperature because of how each molecule of water interacts with its neighbors. In fact, you are a thinking, sentient being because of an on-going series of chemical reactions and other chemical interactions. You can see this text because of how light interacts with molecules called proteins in the back of your eye. Chemistry is often called the central science because it is what connects most of the other sciences together. Chemistry is in some ways physics on a larger scale and in some ways is biology or geology on a smaller scale. Chemistry is used to understand and make better materials for engineering. It is used to understand the chemical mechanisms of disease as well as to create pharmaceuticals to treat disease. Chemistry is somehow involved in almost every science, every technology and every "thing". With such a large area of study, it is impossible to know everything about chemistry and very difficult to summarize the field concisely. Even the most knowledgable, experienced chemist only knows a very narrow area of chemistry better than others. Of course, most chemists have a broad general knowledge of many areas of chemistry as well. Chemistry is divided into many areas of study called subdisciplines in which chemists specialize. The chemistry taught at the high school or early college level is often called "general chemistry" and is intended to be an introduction to a wide variety of fundamental concepts and to give the student the tools to continue on to more advanced subjects. Many concepts presented at this level are often incomplete and technically inaccurate yet of extraordinary utility. Chemists regularly use these simple, elegant tools and explanations in their work when they suffice because the best solution possible is often so overwhelmingly difficult and the true solution is usually unobtainable. The science of chemistry is historically a recent development but has its roots in alchemy which has been practiced for millennia throughout the world. The word chemistry is directly derived from the word alchemy, however the etymology of alchemy is unclear (see alchemy).

Subdisciplines of chemistry

Chemistry typically is divided into several major sub-disciplines. There are also several main cross-disciplinary and more specialized fields of chemistry. ; Analytical chemistry : Analytical chemistry is the analysis of material samples to gain an understanding of their chemical composition and structure. Analytical chemistry incorporates standardized experimental methods in chemistry. These methods may be used in all subdiciplines of chemistry, exluding purely theoretical chemistry. ; Biochemistry : Biochemistry is the study of the chemicals, chemical reactions and chemical interactions that take place in living organisms. Biochemistry and organic chemistry are closely related f.e. in medicinal chemistry. ; Inorganic chemistry : Inorganic chemistry is the study of the properties and reactions of inorganic compounds. The distinction between organic and inorganic disciplines is not absolute and there is much overlap, most importantly in the sub-discipline of organometallic chemistry. ; Organic chemistry : Organic chemistry is the study of the structure, properties, composition, mechanisms, and reactions of organic compounds. ; Physical chemistry : Physical chemistry or physicochemistry is the study of the physical basis of chemical systems and processes. In particular, the energetics and dynamics of such systems and processes are of interest to physical chemists. Important areas of study include chemical thermodynamics, chemical kinetics, electrochemistry, statistical mechanics, and spectroscopy. Physical chemistry has large overlap with molecular physics. ; Theoretical chemistry : Theoretical chemistry is the study of chemistry via theoretical reasoning (usually within mathematics or physics). In particular the application of quantum mechanics to chemistry is called quantum chemistry. Since the end of the second world war, the development of computers has allowed a systematic development of computational chemistry, which is the art of developing and applying computer programs for solving chemical problems. Theoretical chemistry has large overlap with molecular physics. ; Other fields : Astrochemistry, Atmospheric chemistry, Chemical Engineering, Electrochemistry, Environmental chemistry, Geochemistry, History of chemistry, Materials science, Medicinal chemistry, Molecular Biology, Molecular genetics, Nuclear chemistry, Organometallic chemistry, Petrochemistry, Pharmacology, Photochemistry, Phytochemistry, Polymer chemistry, Supramolecular chemistry, Surface chemistry, and Thermochemistry.

Fundamental concepts

Nomenclature

Nomenclature refers to the system for naming chemical compounds. There are well-defined systems in place for naming chemical species. Organic compounds are named according to the organic nomenclature system. Inorganic compounds are named according to the inorganic nomenclature system. See also: IUPAC nomenclature

Atoms

Main article: Atom. An atom is a collection of matter consisting of a positively charged core (the nucleus) which contains protons and neutrons, and which maintains a number of electrons to balance the positive charge in the nucleus.

Elements

Main article: Chemical element. An element is a class of atoms which have the same number of protons in the nucleus. This number is known as the atomic number of the element. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon, and all atoms with 92 protons in their nuclei are atoms of the element uranium. The most convenient presentation of the elements is in the periodic table, which groups elements with similar chemical properties together. Lists of the elements by name, by symbol, and by atomic number are also available. See also: isotope

Compounds

Main article: Chemical compound A compound is a substance with a fixed ratio of chemical elements which determines the composition, and a particular organisation which determines chemical properties. For example, water is a compound containing hydrogen and oxygen in the ratio of two to one, with the Oxygen between the hydrogens, and an angle of 104.5° between them. Compounds are formed and interconverted by chemical reactions.

Molecules

Main article: Molecule. A molecule is the smallest indivisible portion of a pure compound that retains a set of unique chemical properties. A molecule consists of two or more atoms covalently bonded together.

Ions

Main article: Ion. An ion is a charged species, or an atom or a molecule that has lost or gained an electron. Positively charged cations (e.g. sodium cation Na⁺) and negatively charged anions (e.g. chloride Cl^-) can form neutral salts (e.g. sodium chloride NaCl). Examples of polyatomic ions that do not split up during acid-base reactions are hydroxide (OH^-), or phosphate (PO₄^3-).

Bonding

Main article: Chemical bond. A chemical bond is an interaction which holds together atoms in molecules or crystals. In many simple compounds, valence bond theory and the concept of oxidation number can be used to predict molecular structure and composition. Similarly, theories from classical physics can be used to predict many ionic structures. With more complicated compounds, such as metal complexes, valence bond theory fails and alternative approaches which are based on quantum chemistry, such as molecular orbital theory, are necessary.

States of matter

Main article: Phase (matter). A phase is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as pressure or temperature. Physical properties, such as density and refractive index tend to fall within values characteristic of the phase. The phase of matter is defined by the phase transition, which is when energy put into or taken out of the system goes into rearranging the structure of the system, instead of changing the bulk conditions. Sometimes the distinction between phases can be continuous instead of having a discrete boundary, in this case the matter is considered to be in a supercritical state. When three states meet based on the conditions, it is known as a triple point and since this is invariant, it is a convenient way to define a set of conditions. The most familiar examples of phases are solids, liquids, and gases. Less familiar phases include plasmas, Bose-Einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of magnetic materials. Even the familiar ice has many different phases, depending on the pressure and temperature of the system. While most familiar phases deal with three-dimensional systems, it is also possible to define analogs in two-dimensional systems, which is getting a lot of attention because of its relevance to biology.

Chemical reactions

Main article: Chemical reaction. Chemical reactions are transformations in the fine structure of molecules. Such reactions can result in molecules attaching to each other to form larger molecules, molecules breaking apart to form two or more smaller molecules, or rearrangement of atoms within or across molecules. Chemical reactions usually involve the making or breaking of chemical bonds.

Quantum chemistry

Main article: Quantum chemistry. Quantum chemistry describes the behavior of matter at the molecular scale. It is, in principle, possible to describe all chemical systems using this theory. In practice, only the simplest chemical systems may realistically be investigated in purely quantum mechanical terms, and approximations must be made for most practical purposes (e.g., Hartree-Fock, post Hartree-Fock or Density functional theory, see computational chemistry for more details). Hence a detailed understanding of quantum mechanics is not necessary for most chemistry, as the important implications of the theory (principally the orbital approximation) can be understood and applied in simpler terms.

Laws

The most fundamental concept in chemistry is the law of conservation of mass, which states that there is no detectable change in the quantity of matter during an ordinary chemical reaction. Modern physics shows that it is actually energy that is conserved, and that energy and mass are related; a concept which becomes important in nuclear chemistry. Conservation of energy leads to the important concepts of equilibrium, thermodynamics, and kinetics. Further laws of chemistry elaborate on the law of conservation of mass. Joseph Proust's law of definite composition says that pure chemicals are composed of elements in a definite formulation; we now know that the structural arrangement of these elements is also important. Dalton's law of multiple proportions says that these chemicals will present themselves in proportions that are small whole numbers (i.e. 1:2 O:H in water); although in many systems (notably biomacromolecules and minerals) the ratios tend to require large numbers, and are frequently represented as a fraction. Such compounds are known as Non-Stoichiometric Compounds More modern laws of chemistry define the relationship between energy and transformations.
- In equilibrium, molecules exist in mixture defined by the transformations possible on the timescale of the equilibrium, and are in a ratio defined by the intrinsic energy of the molecules—the lower the intrinsic energy, the more abundant the molecule.
- Transforming one structure to another requires the input of energy to cross an energy barrier; this can come from the intrinsic energy of the molecules themselves, or from an external source which will generally accelerate transformations. The higher the energy barrier, the slower the transformation occurs.
- There is a hypothetical intermediate, or transition structure, that corresponds to the structure at the top of the energy barrier. The Hammond-Leffler Postulate states that this structure looks most similar to the product or starting material which has intrinsic energy closest to that of the energy barrier. Stabilizing this hypothetical intermediate through chemical interaction is one way to achieve catalysis.
- All chemical processes are reversible (law of microscopic reversibility) although some processes have such an energy bias, they are essentially irreversible.

History of chemistry

- Alchemy
- Discovery of the chemical elements
- History of chemistry
- Nobel Prize in chemistry
- Timeline of chemical element discovery

Etymology

Old French: alkemie; Arab al-kimia: the art of transformation. See also: alchemy

External links

- [http://www.allchemicals.info/ Chemical Glossary]
- [http://chem.sis.nlm.nih.gov/chemidplus/ Chemistry Information Database includes basic information and some toxicity]
- [http://www.chem.qmw.ac.uk/iupac/ IUPAC Nomenclature Home Page], see especially the "Gold Book" containing definitions of standard chemical terms
- [http://www.cci.ethz.ch/index.html Experiments] videos and photos of the techniques and results
- [http://physchem.ox.ac.uk/MSDS/ Material safety data sheets for a variety of chemicals]
- [http://www.flinnsci.com/search_MSDS.asp Material Safety Data Sheets]

British English

British English (BrE) is a term used to differentiate the form of the written English language in the United Kingdom from other forms of the English language. It is also used by some, particularly Americans, to describe the spoken versions of English used within England. The term is rarely heard within the United Kingdom. British people say that they speak English - but never British - and that others speak English with an accent, such as a 'South African accent'. When speaking, they will often drop the word "accent" and simply say Canadian, American, Jamaican and so on. A less ambiguous term is English English. Although British English can describe the formal written English used in the United Kingdom, the forms of spoken English used in the United Kingdom vary considerably more than in most other areas of the world where English is spoken. Dialects and accents vary not only within regions of the UK, for example in Scotland, Northern Ireland and Wales, but also within England. The written form of the language, as taught in schools, is universally Commonwealth English with a slight emphasis on a few words that might be more common in some areas than in others. For example, although the words "wee" and "small" are interchangeable, one is more likely to see "wee" written by a Scot than by a Londoner. For historical reasons dating back to the rise of London in the 9th century, the variety of language spoken in London and the East Midlands became the standard English within the Court and thus the form of language generally accepted for use in the law, government, literature and education of the British Isles. Like other forms of languages, the English used in Britain changes over time. Although British English is often used in the United States to denote the English spelling and lexicon used outside the US, the term Commonwealth English is more accurate for this purpose. The British spellings were most famously recorded in Samuel Johnson's A Dictionary of the English Language (1755). Historically, the widespread usage of English across the world is attributed to the power once held by the British Empire, and hence the most common form of English used by the British ruling class was the English used in south-east England (in the area around the capital city London, and the main English university towns of Oxford and Cambridge). This form of the language is associated with Received Pronunciation (RP), which is still regarded by many people outside the UK (especially in the United States) as "the British accent". From the second half of the 20th century to the present day, the preeminence of the English language has largely been linked to the economic, military and political dominance of the United States in world affairs, and American English is often regarded as the most prominent form of English in the world today, especially with the large amount of U.S. cultural products (such as films, books, and music) around the world, which is not matched in volume by those from other English-speaking nations. The form of English spoken and particularly written in the United Kingdom still has a major cultural influence on the English used in many Commonwealth countries, including Australia, South Africa, and India, as well as in the European Union. Although British English is taught and used in the former British colonies of Hong Kong, Singapore and Malaysia, American English is often taught in Chinese and Japanese schools, and in other schools throughout Asia.

-ise versus -ize

Words of the sort organize/organise and their derivatives can be spelt with either s or z in British English. The -ize forms are promoted by the Oxford English Dictionary. British English with -ize is sometimes known as OED spelling, and may be marked by the registered IANA language tag 'en-GB-oed'. It is the spelling used by the Encyclopaedia Britannica, by the United Nations, and by many international organizations and academic publications. The -ize forms were used by the London Times until the mid-1980s. The -ise forms are now generally used by the British government, by the European Union and mostly taught in the British school system. They are far more prevalent in common usage. Pam Peters (2004, -ize/-ise) relates that British National Corpus data indicates the ratio of popularity for -ise forms to -ize forms in Britain is 3:2.

Sulfur

Sulfur (or sulphur; see spelling below) is the chemical element in the periodic table that has the symbol S and atomic number 16. It is an abundant, tasteless, odorless, multivalent non-metal. Sulfur, in its native form, is a yellow crystaline solid. In nature, it can be found as the pure element or as sulfide and sulfate minerals. It is an essential element for life and is found in several amino acids. Its commercial uses are primarily in fertilizers but it is also widely used in gunpowder, matches, insecticides and fungicides.

Notable characteristics

fungicide At room temperature, sulfur is a soft bright yellow solid. Although sulfur is infamous for its smell - frequently compared to rotten eggs - the odor is actually characteristic of hydrogen sulfide (H₂S); elemental sulfur is odorless. It burns with a blue flame that emits sulfur dioxide, notable for its peculiar suffocating odor. Sulfur is insoluble in water but soluble in carbon disulfide and other nonpolar solvents. Common oxidation states of sulfur include −2, +2, +4 and +6. Sulfur forms stable compounds with all elements except the noble gases. Sulfur in the solid state ordinarily exists as a cyclic crown-shaped S₈ molecules. Sulfur has many allotropes besides S₈. Removing one atom from the crown gives S₇, which is responsible for sulfur's distinctive yellow color. Many other rings have been prepared, including S₁₂ and S₁₈. By contrast, its lighter neighbor oxygen only exists in two states of chemical significance: O₂ and O₃. Selenium, the heavier analogue of sulfur can form rings but is more often found as a polymer chain. The crystallography of sulfur is complex. Depending on the specific conditions, the sulfur allotropes form several distinct crystal structures, with rhombic and monoclinic S₈ best known. A noteworthy property is that the viscosity of molten sulfur, unlike most other liquids, increases with temperature due to the formation of polymer chains. However, after a certain temperature is reached, the viscosity is reduced because there is enough energy to break the chains. Amorphous or "plastic" sulfur can be produced through the rapid cooling of molten sulfur. 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 catalyzed by human saliva.

Applications

Sulfur has many industrial uses. Through its major derivative, sulfuric acid (H₂SO₄), sulfur ranks as one of the more important elements used as an industrial raw material. It is of prime importance to every sector of the world's economies. Sulfuric acid production is the major end use for sulfur, and consumption of sulfuric acid has been regarded as one of the best indices of a nation's industrial development. More sulfuric acid is produced in the United States every year than any other industrial chemical. Sulfur is also used in batteries, detergents, the vulcanization of rubber, fungicides, and in the manufacture of phosphate fertilizers. Sulfites are used to bleach paper and as a preservative in wine and dried fruit. Because of its flammable nature, sulfur also finds use in matches, gunpowder, and fireworks. Sodium or ammonium thiosulfate are used as photographic fixing agents. Magnesium sulfate, better known as Epsom salts can be used as a laxative, a bath additive, an exfoliant, or a magnesium supplement for plants. In the late 1700's, furniture makers used molten sulfur to produce decorative inlays in their craft. Because of the sulfur dioxide given off during the process of melting sulfur, the craft of sulfur inlays was soon abandoned.

Biological role

The amino acids cysteine and methionine contain sulfur, as do all polypeptides, proteins, and enzymes which contain these amino acids. This makes sulfur a necessary component of all living cells. Disulfide bonds between polypeptides are very important in protein assembly and structure. Homocysteine and taurine are also sulfur containing amino acids but are not coded for by DNA nor are they part of the primary structure of proteins. Some forms of bacteria use hydrogen sulfide (H₂S) in the place of water as the electron donor in a primitive photosynthesis-like process. Sulfur is absorbed by plants from soil as the sulfate ion. Inorganic sulfur forms a part of iron-sulfur clusters, and sulfur is the bridging ligand in the Cu_A site of cytochrome c oxidase. Sulfur is an important component of coenzyme A

Environmental Impact

The burning of coal and petroleum by industry and power plants liberates huge amounts of sulfur dioxide SO₂, which reacts with atmospheric water and oxygen to produce sulfuric acid. This causes acid rain which lowers the pH of soil and freshwater bodies, resulting in substantial damage to the natural environment and chemical weathering of statues and architecture. Fuel standards increasingly require sulfur to be extracted from fossil fuels to prevent the formation of acid rain. This extracted sulfur is then refined and represents a large portion of sulfur production.

History

fossil fuel Sulfur (Sanskrit, sulvere; Latin sulpur) was known in ancient times, and is referred to in the Biblical Pentateuch (Genesis). English translations of this commonly refer to sulfur as "brimstone", giving rise to the name of 'Fire and brimstone' sermons, which are sermons where hell and eternal damnation for sinners is stressed. It is from this part of the Bible that hell is thought to smell of sulfur. The word itself is almost certainly from the Arabic sufra meaning yellow, from the bright color of the naturally-occurring form. Homer mentioned "pest-averting sulfur" in the 9th century BC and in 424 BC, the tribe of Boeotia destroyed the walls of a city by burning a mixture of coal, sulfur, and tar under them. Sometime in the 12th century, the Chinese invented gun powder which is a mixture of potassium nitrate (K N O₃), carbon, and sulfur. Early alchemists gave sulfur its own alchemical symbol which was a triangle at the top of a cross. In the late 1770s, Antoine Lavoisier helped convince the scientific community that sulfur was an element and not a compound. In 1867 sulfur was discovered in underground deposits in Louisiana and Texas. The overlying layer of earth was quicksand, prohibiting ordinary mining operations. Therefore the Frasch process was utilized.

Occurrence

Frasch process Frasch process, New Zealand]] Elemental sulfur can be found near hot springs and volcanic regions in many parts of the world, especially along the Pacific Ring of Fire. These occurrences are the basis for the traditional name brimstone, since sulfur could be found near the brims of volcanic craters. Such volcanic deposits are currently exploited in Indonesia, Chile, and Japan. Significant desposits of elemental sulfur also exist in salt domes along the coast of the Gulf of Mexico, and in evaporites in eastern Europe and western Asia. The sulfur in these deposits is believed to come from the action of anaerobic bacteria on sulfate minerals, especially gypsum. Such deposits are the basis for commercial production in the United States, Poland, Russia, Turkmenistan, and Ukraine. Sulfur extracted from oil, gas and the Athabasca Oil Sands has become a glut on the market, with huge stockpiles of sulfur in existence throughout Alberta. Athabasca Oil Sands]] Common naturally-occurring sulfur compounds include the metal sulfides, such as pyrite (iron sulfide), cinnabar (mercury sulfide), Galena (lead sulfide), sphalerite (zinc sulfide) and stibnite (antimony sulfide); and the metal sulfates, such as gypsum (calcium sulfate), alunite (potassium aluminium sulfate), and barite (barium sulfate). Hydrogen sulfide is the gas responsible for the odor of rotten eggs. It occurs naturally in volcanic emissions, such as from hydrothermal vents, and from bacterial action on decaying sulfur-containing organic matter. The distinctive colors of Jupiter's volcanic moon, Io, are from various forms of molten, solid and gaseous sulfur. There is also a dark area near the Lunar crater Aristarchus that may be a sulfur deposit. Sulfur is also present in many types of meteorites.

Compounds

Hydrogen sulfide has the characteristic smell of rotten eggs. Dissolved in water, hydrogen sulfide is acidic and will react with metals to form a series of metal sulfides. Natural metal sulfides are common, especially those of iron. Iron sulfide is called pyrite, the so called fool's gold. Interestingly, pyrite can show semiconductor properties.[http://home.earthlink.net/~lenyr/iposc.htm] Galena, a naturally occurring lead sulfide, was the first semiconductor discovered, and found a use as a signal rectifier in the "cat's whiskers" of early crystal radios. Many of the unpleasant odors of organic matter are based on sulfur-containing compounds such as ethyl and methyl mercaptan used to scent natural gas so that leaks are easily detectable. The odor of garlic and "skunk stink" are also caused by sulfur containing organic compounds. However, not all organic sulfur compounds smell unpleasant, margin, a sulfur containing terpene is responsible for the characteristic scent of grapefruit. Polymeric sulfur nitride has metallic properties even though it does not contain any metal atoms. This compound also has unusual electrical and optical properties. This polymer can be made from tetrasulfur tetranitride S₄N₄. Other important compounds of sulfur include: INORGANIC:
- Sulfides (S^2-) are simple compounds of sulfur with some other chemical element.
- Sulfites (SO₃^2-), the salts of sulfurous acid, H₂SO₃, created by dissolving SO₂ in water. Sulfurous acid and the corresponding sulfites are fairly strong reducing agents. Other compounds derived from SO₂ include the pyrosulfite or metabisulfite ion (S₂O₅²⁻).
- Sulfates (SO₄^2-), the salts of sulfuric acid. Related to this, sulfuric acid also reacts with SO₃ in equimolar ratios to form pyrosulfuric acid (H₂S₂O₇).
- Thiosulfates (sometimes refered as thiosulfites or "hyposulfites") (S₂O₃²⁻). Thiosulfates are used in photographic fixing (HYPO)as reducing agents and ammonium thiosulfate is being investigated as a cyanide replacement in leaching gold.[http://doccopper.tripod.com/gold/AltLixiv.html]
- Sodium dithionite, Na₂S₂O₄ from hyposulfurous/dithionous acid, a powerful reducing agent.
- Sodium dithionate (Na₂S₂O₆)
- Polythionic acids (H₂S_nO₆), where n can range from 3 to 80.
- Peroxymonosulfuric acid (H₂SO₅) and peroxydisulfuric acids (H₂S₂O₈), made from the action of SO₃ on concentrated H₂O₂, and H₂SO₄ on concentrated H₂O₂ respectively.
- Sodium polisulfides (Na₂S_x)
- Sulfur hexafluoride, SF₆, a heavy, gaseous, non-reactive and non-toxic propellant
- Tetrasulfur tetranitride S₄N₄.
- Thiocyanates are compounds containing the thiocyanate ion, SCN^-. Related to this there is thiocyanogen, (SCN)₂. ORGANIC:
- dimethylsulfoniopropionate (DMSP; (CH₃ )₂S⁺CH₂CH₂COO^-) which is the central component of the marine organic sulfur cycle.
- A thioether is a molecule with the form R-S-R′, where R and R′ are organic groups. These are the sulfur equivalents of ethers.
- A thiol (also known as a mercaptan) is a molecule with an -SH functional group. These are the sulfur equivalents of alcohols.
- A thiolate ion has an -S^- functional group attached. These are the sulfur equivalent of alkoxide ions.
- A sulfoxide is a molecule with an R-S(=O)-R′ functional group where R and R′ are organic groups. A common example of a sulfoxide is DMSO.
- A sulfone is a molecule with an R-S(=O)-R′ functional group where R and R′ are organic groups.
- Lawesson's reagent is a chemical reagent which can remove oxygen from other organic molecules and replace it with sulfur.
- Napthalen-1,8-diyl 1,3,2,4-dithiadiphosphetane 2,4-disulfide

Isotopes

Sulfur has 18 isotopes, of which four are stable: ³²S (95.02%), ³³S (0.75%), ³⁴S (4.21%), and ³⁶S (0.02%). Other than ³⁵S, the radioactive isotopes of sulfur are all short lived. Sulfur-35 is formed from cosmic ray spallation of argon-40 in the atmosphere. It has a half-life of 87 days. When sulfide minerals are precipitated, isotopic equilibration among solids and liquid may cause small differences in the dS-34 values of co-genetic minerals. The differences between minerals can be used to estimate the temperature of equilibration. The dC-13 and dS-34 of co-existing carbonates and sulfides can be used to determine the pH and oxygen fugacity of the ore-bearing fluid during ore formation. In most forest ecosystems, sulfate is derived mostly from the atmosphere; weathering of ore minerals and evaporites also contribute some sulfur. Sulfur with a distinctive isotopic composition has been used to identify pollution sources, and enriched sulfur has been added as a tracer in hydrologic studies. Differences in the natural abundances can also be used in systems where there is sufficient variation in the S-34 of ecosystem components. Rocky Mountain lakes thought to be dominated by atmospheric sources of sulfate have been found to have different dS-34 values from lakes believed to be dominated by watershed sources of sulfate.

Precautions

Carbon disulfide, Carbon oxysulfide, hydrogen sulfide, and sulfur dioxide should all be handled with care. Although sulfur dioxide is sufficiently safe to be used as a food additive in small amounts, at high concentrations it reacts with moisture to form sulfurous acid which in sufficient quantities may harm the lungs, eyes or other tissues. In creatures without lungs such as insects or plants, it otherwise prevents respiration. Hydrogen sulfide is quite toxic (more toxic than cyanide). Although very smelly at first, it quickly deadens the sense of smell, so potential victims may be unaware of its presence until it is too late.

Spelling

The element has traditionally been spelled sulphur in the United Kingdom and India, but sulfur in the United States and Canada, while both spellings are used in Australia and New Zealand. The IUPAC adopted the spelling "sulfur" in 1990, as did the Royal Society of Chemistry Nomenclature Committee in 1992. This spelling has begun to replace its variant in educated circles, unlike aluminum, which did not stick outside the US and Canada.

References

- [http://periodic.lanl.gov/elements/16.html Los Alamos National Laboratory – Sulfur]
- R. Steudel (ed.): Elemental Sulfur and Sulfur-Rich Compounds (part I & II), Topics in Current Chemistry Vol. 230 & 231, Springer, Berlin 2003.

External links

- [http://library.tedankara.k12.tr/chemistry/vol2/allotropy/z129.htm Sulfur phase diagram.]
- [http://www.webelements.com/webelements/elements/text/S/index.html WebElements.com – Sulfur] Category:Chemical elements Category:Nonmetals Category:Chalcogens Category:Pyrotechnic chemicals ko:황 ja:硫黄 simple:Sulfur th:กำมะถัน

Chemical element

A chemical element, often called simply element, is a chemical substance that canot be divided or changed into other chemical substances by any ordinary chemical technique. The smallest unit of this kind of chemical substances is an atom. An element is a class of substances that contain the same number of protons in all its atoms.

Chemistry terminology

Earlier an element or pure element was defined as a substance which "cannot be further broken down into another compound with different chemical properties" -- which should be taken to mean it consists of atoms of one element. However, due to allotropy, the isotope effect, and the confusion with the more useful term referring to the general class of atoms (irrespective of what compound it may be in), this usage is in disfavor amongst contemporary chemists, and sees restricted, mostly historical, use. This definition was motivated by the observation that these elements could not be dissociated by chemical means into other compounds. For example, water could be converted into hydrogen and oxygen, but hydrogen and oxygen could not be further decomposed, thus "elemental". There are also many counterexamples (for example "elemental oxygen" (O₂) can be decomposed by solely chemical means into oxygen ions and atoms which have drastically different chemical properties). The remainder of this article will concern itself with the first definition.

Description

The atomic number of an element, Z, is equal to the number of protons which defines the element. For example, all carbon atoms contain 6 protons in their nucleus, so for carbon Z=6. These atoms may have different amounts of neutrons, and are known as isotopes of the element. The atomic mass of an element, A, is measured in unified atomic mass units (u) is the average mass of all the atoms of the element in an environment of interest (usually the earth's crust and atmosphere). Since electrons are light, and neutrons are barely more than the mass of the proton, this usually corresponds to the sum of the protons and neutrons in the nucleus of the most abundant isotope, though this is not always the case (notably chlorine, which is about three-quarters ³⁵Cl and a quarter ³⁷Cl). Some isotopes are radioactive and decay into other elements upon radiating an alpha or beta particle. Some elements have no nonradioactive isotopes, in particular all elements with Z >= 84. The lightest elements are hydrogen and helium. Hydrogen is thought to be the first element to appear after the Big Bang. All the heavier elements, are made naturally and artificially through various methods of nucleosynthesis. As of 2005, there are 116 known elements: 93 occur naturally on earth (including technetium and plutonium), and 94 (including promethium) have been detected so far in the universe. The 23 elements not found on earth are derived artificially; the first purportedly synthesized element was technetium, in 1937, although the trace amounts of naturally occurring technetium were not known then. All artificially derived elements are radioactive with short half-lives so that any such atoms that were present at the formation of Earth are extremely likely to have already decayed. Lists of the elements by name, by symbol, by atomic number, by density, by melting point and by boiling point are available. The most convenient presentation of the elements is in the periodic table, which groups elements with similar chemical properties together.

Nomenclature

The naming of elements precedes the atomic theory of matter, although at the time it was not known which chemicals were elements and which compounds. When it was learned, existing names (e.g., gold, mercury, iron) were kept in most countries, and national differences emerged over the names of elements either for convenience, linguistic niceties, or nationalism. For example, the Germans use "Wasserstoff" for "hydrogen" and "Sauerstoff" for "oxygen," while some romance languages use "natrium" for "sodium" and "kalium" for "potassium," and the French prefer the obsolete but historic term "azote" for "nitrogen." But for international trade, the official names of the chemical elements both ancient and recent are decided by the International Union of Pure and Applied Chemistry, which has decided on a sort of international English language. That organization has recently prescribed that "aluminium" and "caesium" take the place of the US spellings "aluminum" and "cesium," while the US "sulfur" takes the place of the British "sulphur." But chemicals which are practicable to be sold in bulk within many countries, however, still have national names, and those which do not use the Latin alphabet cannot be expected to use the IUPAC name. According to IUPAC, the full name of an element is not capitalized, even if it is derived from a proper noun (unless it would be capitalized by some other rule, for instance if it begins a sentence). And in the second half of the twentieth century physics laboratories became able to produce nuclei of chemical elements that have too quick a decay rate to ever be sold in bulk. These are also named by IUPAC, which generally adopts the name chosen by the discoverer. This can lead to the controversial question of which research group actually discovered an element, a question which delayed the naming of elements with atomic number of 104 and higher for a considerable time. (See element naming controversy). Precursors of such controversies involved the nationalistic namings of elements in the late nineteenth century (e.g., as "lutetium" refers to Paris, France, the Germans were reticent about relinquishing naming rights to the French, often calling it "cassiopeium"). And notably, the British discoverer of "niobium" originally named it "columbium," after the New World, though this did not catch on in Europe. The Americans had to accept the international name just when it was becoming an economically important material late in the twentieth century.

Chemical symbols

Specific chemical elements

Before chemistry became a science, alchemists had designed arcane symbols for both metals and common compounds. These were however used as abbreviations in diagrams or procedures; there was no concept of one atoms combining to form molecules. With his advances in the atomic theory of matter, John Dalton devised his own simpler symbols, based on circles, which were to be used to depict molecules. These were superseded by the current typographical system in which chemical symbols are not used as mere abbreviations though each consists letters of the Latin alphabet - they are symbols intended to be used by peoples of all languages and alphabets. The first of these symbols were intended to be fully international, for they were based on the Latin abbreviations of the names of metals: Fe comes from Ferrum; Ag from Argentum. The symbols were not followed by a period (full stop) as abbreviations were. Besides a name, later chemical elements are also given a unique chemical symbol, based on the name of the element, not necessarily derived from the colloquial English name. (e.g., sodium has chemical symbol 'Na' after the Latin natrium). The same applies to "W" (wolframium) for Tungsten , "Hg" (Hydrargyrum) for mercury and "K" for potassium. Stricly taken, a symbol like Tu for tungsten or M or Me for mercury seems to be more logical. Chemical symbols are understood internationally when element names might need to be translated. There are sometimes differences; for example, the Germans have used "J" instead of "I" for iodine, so the character would not be confused with a roman numeral. The first letter of a chemical symbol is always capitalized, as in the preceding examples, and the subsequent letters, if any, are always minuscule (small letters).

General chemical symbols

There are also symbols for series of chemical elements, for comparative formulas. These are one capital letter in length, and the letters are reserved so they are not permitted to be given for the names of specific elements. For example, an "X" is used to indicate a variable group amongst a class of compounds (though usually a halogen), while "R" is used for a radical (not to be confused with radical_(chemistry), meaning a compound structure such as a hydrocarbon chain. The letter "Q" is reserved for "heat" in a chemical reaction. "Y" is also often used as a general chemical symbol, although it is also the symbol of Yttrium. "Z" is also frequently used as a general variable group. "L" is used to represent a general ligand in inorganic and organometallic chemistry. "M" is also often used in place of a general metal.

Nonelement symbols

Nonelements, especially in organic and organometallic chemistry, often acquire symbols which are inspired by the elemental symbols. A few examples: Cy - cyclohexyl; Ph - phenyl; Bz - benzoyl; Bn - benzyl; Cp - Cyclopentadiene; Pr - propyl; Me - methyl; Et - ethyl; Tf - triflate; Ts - tosyl.

External links

- [http://www.vanderkrogt.net/elements/ Elementymology & Elements Multidict] word history and language dictionary

Chemical information

- [http://www.webelements.com/ WebElements]
- [http://www.vcs.ethz.ch/chemglobe/ptoe/ ChemGlobe]
- [http://pearl1.lanl.gov/periodic/default.htm Los Alamos National Laboratory]
- [http://www.chemicalelements.com/ ChemicalElements] ko:화학 원소 ms:Unsur kimia ja:元素 simple:Element th:ธาตุเคมี

Covalent

.]] Covalent bonding is an intramolecular form of chemical bonding characterized by the sharing of one or more pairs of electrons between two species, producing a mutual attraction that holds the resultant molecule together. Atoms tend to share electrons in such a way that their outer electron shells are filled. Such bonds are always stronger than the intermolecular hydrogen bond and similar in strength to or stronger than the ionic bond. Covalent bonding most frequently occurs between atoms with similar electronegativities. For this reason, non-metals tend to engage in covalent bonding more readily since metals have access to metallic bonding, where the easily-removed electrons are more free to roam about. For non-metals, liberating an electron is more difficult, so sharing is the only option when confronted with another species of similar electronegativity. However, covalent bonding involving metals is particularly important, especially in industrial catalysis and process chemistry. Many polymerization techniques require catalysis involving metal-organic covalent bonds. In their more useful applications, metals often engage in more exotic covalent bonding, such as those between a metal and the σ bond of molecular hydrogen, or between a metal and the π bond of an alkane or alkene.

History

alkene The idea of covalent bonding can be traced to Gilbert N. Lewis, who in 1916 described the sharing of electron pairs between atoms. He introduced the so called Lewis Notation or Electron Dot Notation in which valence electrons (those in the outer shell) are represented as dots around the atomic symbols. Pairs of electrons located between atoms represent covalent bonds. Multiple pairs represent multiple bonds, such as double and triple bonds. Some examples of Electron Dot Notation are shown in the following figure. An alternative form, in which bond-forming electron pairs are represented as solid lines, is shown in blue. While the idea of shared electron pairs provides an effective qualitative picture of covalent bonding, quantum mechanics is needed to understand the nature of these bonds and predict the structures and properties of simple molecules. Heitler and London are credited with the first successful quantum mechanical explanation of a chemical bond, specifically that of molecular hydrogen, in 1927. Their work was based on the valence bond model, which assumes that a chemical bond is formed when there is good overlap between the atomic orbitals of participating atoms. These atomic orbitals are known to have specific angular relationships between each other, and thus the valence bond model can successfully predict the bond angles observed in simple molecules.

Bond Polarity

There are two types of covalent bonds: Polar covalent bonds, and non-polar (or pure) covalent bonds. The most widely accepted definition of polar covalent is when the atoms involved have an electronegativity difference that is less than 1.67 (though some texts read 1.7), but greater than zero. A pure covalent bond is a bond that occurs when the atoms involved have an electronegativity difference of zero (though some texts read less than 0.2). Pure covalent bonds (which are usually non-soluble, electrically non-conductive and tend to exist as individual molecules), and ionic bonds (which conversely are soluble, electrically conductive when molten or in solution and generally tend to exist in a crystalline form) are on two opposite ends of the figurative spectrum and have differing properties. Polar covalent bonds fall in the middle and have properties of both.

Bond order

Bond order is a term that describes the number of pairs of electrons shared between atoms forming a covalent bond. The most common type of covalent bond is the single bond, the sharing of only one pair of electrons between two individual atoms. All bonds with more than one shared pair are called multiple covalent bonds. The sharing of two pairs is called a double bond and the sharing of three pairs is called a triple bond. An example of a double bond is nitrous acid (between N and O), and an example of a triple bond is in hydrogen cyanide (between C and N). A single bond usually consists of one sigma bond, a double bond of one sigma and one pi bond, and a triple bond of one sigma and two pi bonds. Quadruple bonds, though rare, also exist. Both carbon and silicon can theoretically form these; however, the formed molecules are explosively unstable. Stable quadruple bonds are observed as transition metal-metal bonds, usually between two transition metal atoms in organometallic compounds. Molybdenum and Ruthenium are the elements most commonly observed with this bonding configuration. An example of a quadruple bond is also found in Di-tungsten tetra(hpp). Quintuple Bonds are found to exist in certain chromium dimers. Sextuple bonds of order 6 have also been observed in transition metals in the gaseous phase at very low temperatures and are extremely rare. Other more exotic bonds, such as three center bonds are known and defy the conventions of bond order. It is also important to note that bond order is an integer value only in the elementary sense and is often fractional in more advanced contexts.

Coordinate covalent bonds

A special case is called a dative covalent bond, also known as a coordinate covalent bond, which occurs when one atom gives both of the electrons in the bond.

Rigidity

Typically, two atoms can rotate about a single bond with relative ease. However, double and triple bonds are very difficult to rotate because they require p orbital overlap. p orbital overlaps are parallel.

Resonance

Some structures can have more than one valid Lewis Dot Structure (for example, ozone, O₃). In an LDS diagram of O₃, the center atom will have a single bond with one atom and a double bond with the other. The LDS diagram cannot tell us which atom has the double bond; the first and second adjoining atoms have equal chances of having the double bond. These two possible structures are called resonance structures. In reality, the structure of ozone is a resonance hybrid between its two possible resonance structures. Instead of having one double bond and one single bond, there are actually two 1.5 bonds with approximately three electrons in each at all times. A special resonance case is exhibited in aromatic rings of atoms (for example, benzene). Aromatic rings are composed of atoms arranged in a circle (held together by covalent bonds) that alternate between single and double bonds according to their LDS. In actuality, the electrons tend to be disambiguously and evenly spaced within the ring. Electron sharing in aromatic structures is often represented with a ring inside the circle of atoms.

Current theory

Today the valence bond model has been supplemented with the molecular orbital model. In this model, as atoms are brought together, the atomic orbitals interact to form hybrid molecular orbitals. These molecular orbitals are a cross between the original atomic orbitals and generally extend between the two bonding atoms. Using quantum mechanics it is possible to calculate the electronic structure, energy levels, bond angles, bond distances, dipole moments, and frequency spectra of simple molecules with a high degree of accuracy. Currently, bond distances and angles can be calculated as accurately as they can be measured (distances to a few pm and bond angles to a few degrees). For small molecules, energy calculations are sufficiently accurate to be useful for determining thermodynamic heats of formation and kinetic activation energy barriers.

External links

- [http://wps.prenhall.com/wps/media/objects/602/616516/Chapter_07.html Covalent Bonds and Molecular Structure] Category:Chemical bonding ja:共有結合

Hydrogen sulfide

:For an alternative meaning of H2S, see H2S radar. Hydrogen sulfide (hydrogen sulphide in British English), H₂S, is a colorless, toxic, flammable gas that is responsible for the foul odor of rotten eggs. It often results when bacteria break down organic matter in the absence of oxygen, such as in swamps and sewers. It also occurs in volcanic gases, natural gas and some well waters. Hydrogen sulfide is also known as sulfane, sulfur hydride, dihydrogen monosulfide, sulfurated hydrogen, sewer gas and stink damp. IUPAC accepts the names "hydrogen sulfide" and "sulfane"; the latter one is used exclusively when naming more complicated compounds.
Chemistry
Hydrogen sulfide is a covalent hydride chemically similar to water (H₂O) since oxygen and sulfur occur in the same periodic table group. The gas is weakly acidic, dissociating in solution into hydrogen cations H⁺ and the hydrosulfide anion HS⁻: ::H₂S → HS⁻ + H⁺ :::K_a = 1.3×10⁻⁷ mol/L; pK_a = 6.89. The sulfide ion, S²⁻, is known in the solid state but not in aqueous solution (c.f. oxide). The second dissociation constant of hydrogen sulfide is often stated to be around 10⁻¹³, but it is now clear that this is an error caused by oxidation of the sulfur in alkaline solution. The current best estimate for pK_a2 is 19±2. Hydrogen sulfide reacts with alkalis and metals to produce sulfides, the salts of hydrogen sulfide (not to be confused with sulfites, which are certain compounds that contain sulfur and oxygen.) Metal sulfides are often black; silver jewelry turns black over time because hydrogen sulfide from the air reacts with the silver to produce silver sulfide. Hydrogen sulfide penetrates the lattice of some steels and makes them brittle, leading to sulphide stress cracking - a concern especially for handling acid gas and sour crude in the oil industry. Small amounts of hydrogen sulfide can be disposed by burning it to sulfur dioxide, which is also corrosive but less toxic.
Occurrence
Hydrogen sulfide occurs naturally in crude petroleum, natural gas (even up to 28%), volcanic gases, and some hot springs. Sulfate-reducing bacteria obtain their energy by using sulfates to oxidize organic matter or hydrogen, thereby reducing the sulfates to hydrogen sulfide. They are especially efficient in low-oxygen environments, such as in swamps and standing waters. Sulfur-reducing bacteria and some archaea obtain their energy by using elemental sulfur to oxidize organic matter or hydrogen, thus also producing hydrogen sulfide. Some other anaerobic bacteria liberate hydrogen sulfide when they digest sulfur-containing amino acids, for instance during the decay of organic matter. Hydrogren sulfide producing bacteria also operate in the human colon, and the odor of flatulence is largely due to trace amounts of the gas. They can also be found in the mouth and contribute to bad breath. Hydrogen sulfide can also result from industrial activities, such as food processing, sewage treatment, coke ovens, paper mills (using the sulphate method), tanneries, and petroleum refineries, in coal mines (as iron sulfides such as pyrite decompose) and anywhere where sulfur comes in contact with organic material at high temperatures. Anthropogenic emissions of hydrogen sulfide are however just 10% of total global emissions. Normal average concentration in clean air is about 0.0001-0.0002 ppm. Hydrogen sulfide can be present naturally in well water. In such cases, ozone is often used for its removal. An alternative method uses a filter with manganese dioxide. Both methods oxidize sulfides to fairly non-toxic sulfates.
Manufacture and use
Hydrogen sulfide used to have importance in analytical chemistry for well over a century, in the qualitative chemical analysis of metal ions. For such small-scale laboratory use the gas is made as needed in a Kipp generator (also known as Kipp's aparatus, named after its inventor Petrus Johannes Kipp) by reaction of sulfuric acid with ferrous sulfide FeS. Industrial production focuses on separation of hydrogen sulfide from sour gas - natural gas with high content of H₂S. The most important industrial use of hydrogen sulfide is as a source of about 25% of the world production of elemental sulphur. The manufacturing process is based on burning about 1/3 of hydrogen sulfide to sulphur dioxide, then letting the resulting SO₂ react with H_{2_{S.

Other uses are in metallurgy for the preparation of metallic sulfides. It also finds use in preparation of phosphors and oil additives, in separation of metals, removal of metallic impurities, and in organic chemical synthesis. Hydrogen sulfide is also used in nuclear engineering, in the Girdler Sulfide process of manufacturing heavy water.

Dangers
The gas is highly toxic and can kill or seriously injure exposed persons. It is heavier than air, so tends to concentrate at the bottom of poorly ventilated spaces - deep wells, sewers, underground tanks. It is also highly flammable, forming explosive mixture with air over a wide range of concentrations (4.3-46%, or 43000-460000 ppm).

Hydrogen sulfide created in sewage has an insidious behavior. When the sewage is allowed to stand for long time, hydrogen sulfide can build up in high concentration - up to 6000 ppm, and then gets quickly released when the liquid is disturbed, rapidly building up fatal concentration. This can happen even in open spaces, when opening manhole covers; a stream of escaping gas can be - and often is - deadly. Due to the fast action of the gas in high concentration loss of consciousness is possible even after a single breath. Attempts to rescue unconscious people from spaces with high concentration of hydrogen sulfide often lead to the death of rescuers (so called "second man fatalities").

Health effects
Hydrogen sulfide is considered a broad-spectrum poison, meaning it can poison several different systems in the body, in particular the nervous system. Its toxicity is comparable with hydrogen cyanide. It forms a complex bond with iron in the mitochondrial cytochrome enzymes, thereby blocking oxygen from binding and stopping cellular respiration.

Poisoning can happen by inhalation of hydrogen sulfide or ingestion of soluble sulfides; absorption through skin is low. Breathing hydrogen sulfide may paralyze the olfactory nerve (making it impossible to smell the gas) and can cause death within just a few breaths. There could be loss of consciousness after one or more breaths. Cases of acute hydrogen sulfide poisonings are rare, occurring mostly in industrial settings; however, emergency physicians should be aware of its symptoms, as quick identification and treatment is critical. An interesting diagnostic clue is discoloration of copper coins in the pockets of the patient. Treatment involves immediate inhalation of amyl nitrite, injections of sodium nitrite, inhalation of pure oxygen, administration of bronchodilators to overcome eventual bronchospasm, and in some cases hyperbaric oxygen therapy.

Exposure to lower concentrations can result in eye irritation (because of the high alkality of the SH^- anion), a sore throat and cough, shortness of breath, and fluid in the lungs. These symptoms usually go away in a few weeks. Long-term, low-level exposure may result in fatigue, loss of appetite, headaches, irritability, poor memory, and dizziness. Higher concentrations of 700-800 ppm tend to be fatal.

- 0.0047 ppm is the recognition threshold, the concentration at which 50% of humans can detect the characteristic rotten egg odor of hydrogen sulfide [http://www.extension.iastate.edu/Publications/PM1963A.pdf]

- 10-20 ppm is the borderline concentration for eye irritation.

- 50-100 ppm leads to eye damage.

- At 150-250 ppm the olfactory nerve is paralyzed after a few inhalations, and the sense of smell disappears, often together with awareness of danger,

- 320-530 ppm leads to pulmonary edema with the possibility of death.

- 530-1000 ppm causes strong stimulation of the central nervous system and rapid breathing, leading to loss of breathing;

- 800 ppm is the lethal concentration for 50% of humans for 5 minutes exposition (LC50).

- Concentrations over 1000 ppm cause immediate collapse with loss of breathing, even after inhalation of a single breath.

Animal studies showed that pigs that ate food containing hydrogen sulfide had diarrhea after a few days and weight loss after about 105 days.

According to Lee R. Kump, a geoscientist from Penn State University, a buildup of hydrogen sulfide in the atmosphere could have caused the Permian-Triassic extinction event 252 million years ago.

There is some evidence that hydrogen sulfide produced by sulfate-reducing bacteria in the colon may cause or contribute to ulcerative colitis.

Function in the body
Hydrogen sulfide is produced in small amounts by some cells of the mammalian body and has a number of biological functions. (Only two other such gases are currently known: nitric oxide NO and carbon monoxide CO.) It is produced from cysteine by various enzymes. It acts as a vasodilator and is also active in the brain, where it increases the response of the NMDA receptor and facilitates long term potentiation, which is involved in the formation of memory. Eventually the gas is converted to sulfites and further oxidized to thiosulfate and sulfate.

In Alzheimer's disease, the concentration of hydrogen sulfide in the brain is abnormally low; in trisomy 21 the body produces an excess of hydrogen sulfide.

Induced hibernation
In 2005, Mark Roth and other scientists from the University of Washington and the Fred Hutchinson Cancer Research Center in Seattle demonstrated that mice can be put into a state of suspended animation by applying a low dosage of hydrogen sulfide (80 ppm H₂S) in the air. The breathing rate of the animals sank from 120 to 10 breaths per minute and their temperature fell from 37 °C to 2 °C above ambient temperature (in effect, they had become cold-blooded).
The mice survived this procedure for 6 hours and afterwards showed no negative health consequences.

Such a hibernation occurs naturally in many mammals and also in toads, but not in mice. (Mice can fall into a state called clinical torpor when food shortage occurs). If the H₂S-induced hibernation can be made to work in humans, it could be useful in the emergency management of severely injured patients, and in the conservation of donated organs.

As mentioned above, hydrogen sulfide binds to cytochrome oxidase and thereby prevents oxygen from binding, which apparently leads to the dramatic slowdown of metabolism. Animals and humans naturally produce some hydrogen sulfide in their body; researchers have proposed that the gas is used to regulate metabolic activity and body temperature, which would explain the above findings.

Participant in the sulfur cycle
Hydrogen sulfide is a major participant in the sulfur cycle, the biogeochemical cycle of sulfur on Earth. As mentioned above, sulfur-reducing and sulfate-reducing bacteria derive energy from converting sulfur or sulfate into hydrogen sulfide by oxidizing hydrogen or organic molecules. Other bacteria liberate hydrogen sulfide from sulfur-containing amino-acids. Several groups of bacteria can use hydrogen sulfide as fuel, oxidizing it to elemental sulfur or to sulfate by using oxygen or nitrate as oxidant. The purple sulfur bacteria and the green sulfur bacteria use hydrogen sulfide as electron donor in photosynthesis, thereby producing elemental sulfur. (In fact, this mode of photosynthesis is older than the mode of cyanobacteria, algae and plants which uses water as electron donor and liberates oxygen.)

Reference
# Giggenbach, W. (1971).}}Inorg. Chem. 10:1333. Meyer, B.; Ward, K.; Koshlap, K.; & Peter, L. (1983). Inorg. Chem. 22:2345. Myers, R. J. (1986). J. Chem. Educ. 63:687.
External links

- [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc01/icsc0165.htm International Chemical Safety Card 0165]
- [http://www.inchem.org/documents/cicads/cicads/cicad53.htm Concise International Chemical Assessment Document 53]
- [http://www.cdc.gov/niosh/npg/npgd0337.html NIOSH Pocket Guide to Chemical Hazards]
- [http://ptcl.chem.ox.ac.uk/MSDS/HY/hydrogen_sulfide.html MSDS safety data sheet]
- [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15329822&query_hl=7 Abstract of survey article on H₂S as used by the body], by P. Kamoun
- [http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/4469793.stm BBC about suspended animation by H₂S]
- [http://www.compchemwiki.org/index.php?title=Hydrogen_sulfide Computational Chemistry Wiki] Category:Sulfides Category:Hydrogen compounds ja:硫化水素

Thioether

A thioether (also known as a sulfide) is a functional group in organic chemistry that has the structure R-S-R, where R is any organic group. A thioether is similar to an ether except that it contains a sulfur atom in place of the oxygen. Because the chemical properties of both atoms are similar, as they are in the same group in the periodic table, the chemical properties of the two functional groups are similar as well. This functional group has minor importance in biology, most notably in the amino acid methionine. One characteristic feature of thioethers, like other sulfur containing compounds, is that simple volatile thioethers have foul odors. One difference from ethers is that ethers (R-O-R) can only be readily oxidized to peroxides (R-O-O-R), whereas thioethers (R-S-R) can be oxidized either to disulfides (R-S-S-R) or to sulfoxides (R-S(=O)-R), which can themselves be oxidized to sulfones (R-S(=O)₂-R). Biochemically, a thioether linkage is formed when a vinyl group reacts with a sulfhydryl group, splitting the double bond and attaching the sulfur atom to the carbon atom not attached to the parent molecule, as follows: R-CH=CH₂ + HS-R' -> R-CH₂-CH₂-S-R'
- Category:Functional groups ja:スルフィド

Organic compound

An organic compound is any member of a large class of chemical compounds whose molecules contain carbon, with the exception of carbides, carbonates, carbon oxides and gases containing carbon.The study of organic compounds is termed organic chemistry. Many of these compounds, such as proteins,

Sulfide

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-ise versus -ize

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Thioether

Organic compound