1.
Chemical compound
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A chemical compound is an entity consisting of two or more atoms, at least two from different elements, which associate via chemical bonds. Many chemical compounds have a numerical identifier assigned by the Chemical Abstracts Service. For example, water is composed of two atoms bonded to one oxygen atom, the chemical formula is H2O. A compound can be converted to a different chemical composition by interaction with a chemical compound via a chemical reaction. In this process, bonds between atoms are broken in both of the compounds, and then bonds are reformed so that new associations are made between atoms. Schematically, this reaction could be described as AB + CD → AC + BD, where A, B, C, and D are each unique atoms, and AB, CD, AC, and BD are each unique compounds. A chemical element bonded to a chemical element is not a chemical compound since only one element. Examples are the diatomic hydrogen and the polyatomic molecule sulfur. Chemical compounds have a unique and defined chemical structure held together in a spatial arrangement by chemical bonds. Pure chemical elements are not considered chemical compounds, failing the two or more atom requirement, though they often consist of molecules composed of multiple atoms. There is varying and sometimes inconsistent nomenclature differentiating substances, which include truly non-stoichiometric examples, from chemical compounds, other compounds regarded as chemically identical may have varying amounts of heavy or light isotopes of the constituent elements, which changes the ratio of elements by mass slightly. Characteristic properties of compounds include that elements in a compound are present in a definite proportion, for example, the molecule of the compound water is composed of hydrogen and oxygen in a ratio of 2,1. In addition, compounds have a set of properties. The physical and chemical properties of compounds differ from those of their constituent elements, however, mixtures can be created by mechanical means alone, but a compound can be created only by a chemical reaction. Some mixtures are so combined that they have some properties similar to compounds. Other examples of compound-like mixtures include intermetallic compounds and solutions of metals in a liquid form of ammonia. Compounds may be described using formulas in various formats, for compounds that exist as molecules, the formula for the molecular unit is shown. For polymeric materials, such as minerals and many metal oxides, the elements in a chemical formula are normally listed in a specific order, called the Hill system
2.
Carbon
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Carbon is a chemical element with symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds, three isotopes occur naturally, 12C and 13C being stable, while 14C is a radioactive isotope, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity, Carbon is the 15th most abundant element in the Earths crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is the second most abundant element in the body by mass after oxygen. The atoms of carbon can bond together in different ways, termed allotropes of carbon, the best known are graphite, diamond, and amorphous carbon. The physical properties of carbon vary widely with the allotropic form, for example, graphite is opaque and black while diamond is highly transparent. Graphite is soft enough to form a streak on paper, while diamond is the hardest naturally occurring material known, graphite is a good electrical conductor while diamond has a low electrical conductivity. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal conductivities of all known materials, all carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form. They are chemically resistant and require high temperature to react even with oxygen, the most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and transition metal carbonyl complexes. The largest sources of carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil. For this reason, carbon has often referred to as the king of the elements. The allotropes of carbon graphite, one of the softest known substances, and diamond. It bonds readily with other small atoms including other carbon atoms, Carbon is known to form almost ten million different compounds, a large majority of all chemical compounds. Carbon also has the highest sublimation point of all elements, although thermodynamically prone to oxidation, carbon resists oxidation more effectively than elements such as iron and copper that are weaker reducing agents at room temperature. Carbon is the element, with a ground-state electron configuration of 1s22s22p2. Its first four ionisation energies,1086.5,2352.6,4620.5 and 6222.7 kJ/mol, are higher than those of the heavier group 14 elements. Carbons covalent radii are normally taken as 77.2 pm,66.7 pm and 60.3 pm, although these may vary depending on coordination number, in general, covalent radius decreases with lower coordination number and higher bond order. Carbon compounds form the basis of all life on Earth
3.
Petrochemical
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Petrochemicals, also called petroleum distillates, are chemical products derived from petroleum. Some chemical compounds made from petroleum are also obtained from fossil fuels, such as coal or natural gas. The two most common classes are olefins and aromatics. Oil refineries produce olefins and aromatics by fluid catalytic cracking of petroleum fractions, chemical plants produce olefins by steam cracking of natural gas liquids like ethane and propane. Aromatics are produced by catalytic reforming of naphtha, Olefins and aromatics are the building-blocks for a wide range of materials such as solvents, detergents, and adhesives. Olefins are the basis for polymers and oligomers used in plastics, resins, fibers, elastomers, lubricants, global ethylene and propylene production are about 115 million tonnes and 70 million tonnes per annum, respectively. Aromatics production is approximately 70 million tonnes, the largest petrochemical industries are located in the USA and Western Europe, however, major growth in new production capacity is in the Middle East and Asia. There is substantial inter-regional petrochemical trade, primary petrochemicals are divided into three groups depending on their chemical structure, Olefins includes ethylene, propylene, and butadiene. Ethylene and propylene are important sources of chemicals and plastics products. Butadiene is used in making synthetic rubber, aromatics includes benzene, toluene, and xylenes. Benzene is a raw material for dyes and synthetic detergents, manufacturers use xylenes to produce plastics and synthetic fibers. Synthesis gas is a mixture of carbon monoxide and hydrogen used to make ammonia, ammonia is used to make the fertilizer urea and methanol is used as a solvent and chemical intermediate. The prefix petro- is an abbreviation of the word petroleum, since petro- is Ancient Greek for rock. Therefore, the correct term would be oleochemicals. However, the term oleochemical is used to describe chemicals derived from plant, benzene, toluene and xylenes, as a whole referred to as BTX and primarily obtained from petroleum refineries by extraction from the reformate produced in catalytic reformers. Methane and BTX are used directly as feedstocks for producing petrochemicals, the output ethylene capacity of large steam crackers ranged up to as much as 1.0 –1.5 Mt per year. Steam crackers are not to be confused with steam reforming plants used to produce hydrogen, like commodity chemicals, petrochemicals are made on a very large scale. Petrochemical manufacturing units differ from commodity chemical plants in that often produce a number of related products
4.
Organic chemistry
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Study of structure includes many physical and chemical methods to determine the chemical composition and the chemical constitution of organic compounds and materials. In the modern era, the range extends further into the table, with main group elements, including, Group 1 and 2 organometallic compounds. They either form the basis of, or are important constituents of, many products including pharmaceuticals, petrochemicals and products made from them, plastics, fuels and explosives. Before the nineteenth century, chemists generally believed that compounds obtained from living organisms were endowed with a force that distinguished them from inorganic compounds. According to the concept of vitalism, organic matter was endowed with a vital force, during the first half of the nineteenth century, some of the first systematic studies of organic compounds were reported. Around 1816 Michel Chevreul started a study of soaps made from various fats and he separated the different acids that, in combination with the alkali, produced the soap. Since these were all compounds, he demonstrated that it was possible to make a chemical change in various fats, producing new compounds. In 1828 Friedrich Wöhler produced the chemical urea, a constituent of urine, from inorganic starting materials. The event is now accepted as indeed disproving the doctrine of vitalism. In 1856 William Henry Perkin, while trying to manufacture quinine accidentally produced the organic dye now known as Perkins mauve and his discovery, made widely known through its financial success, greatly increased interest in organic chemistry. A crucial breakthrough for organic chemistry was the concept of chemical structure, ehrlich popularized the concepts of magic bullet drugs and of systematically improving drug therapies. His laboratory made decisive contributions to developing antiserum for diphtheria and standardizing therapeutic serums, early examples of organic reactions and applications were often found because of a combination of luck and preparation for unexpected observations. The latter half of the 19th century however witnessed systematic studies of organic compounds, the development of synthetic indigo is illustrative. The production of indigo from plant sources dropped from 19,000 tons in 1897 to 1,000 tons by 1914 thanks to the methods developed by Adolf von Baeyer. In 2002,17,000 tons of indigo were produced from petrochemicals. In the early part of the 20th Century, polymers and enzymes were shown to be large organic molecules, the multiple-step synthesis of complex organic compounds is called total synthesis. Total synthesis of natural compounds increased in complexity to glucose. For example, cholesterol-related compounds have opened ways to synthesize complex human hormones, since the start of the 20th century, complexity of total syntheses has been increased to include molecules of high complexity such as lysergic acid and vitamin B12
5.
Carbide
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In chemistry, a carbide is a compound composed of carbon and a less electronegative element. Carbides can be classified by chemical bonding type as follows, salt-like, covalent compounds, interstitial compounds. Examples include calcium carbide, silicon carbide, tungsten carbide, and cementite, the naming of ionic carbides is not systematic. Salt-like carbides are composed of highly electropositive elements such as the metals, alkaline earth metals, and group 3 metals, including scandium, yttrium. Aluminium from group 13 forms carbides, but gallium, indium and these materials feature isolated carbon centers, often described as C4−, in the methanides or methides, two-atom units, C22−, in the acetylides, and three-atom units, C34−, in the sesquicarbides. The graphite intercalation compound KC8, prepared from vapour of potassium and graphite, carbides of this class decompose in water producing methane. Three such examples are aluminium carbide Al 4C3, magnesium carbide Mg 2C, transition metal carbides are not saline carbides but their reaction with water is very slow and is usually neglected. For example, depending on surface porosity, 5–30 atomic layers of titanium carbide are hydrolyzed, forming methane within 5 minutes at ambient conditions, several carbides are assumed to be salts of the acetylide anion C22–, which has a triple bond between the two carbon atoms. Alkali metals, alkaline metals, and lanthanoid metals form acetylides, e. g. sodium carbide Na2C2, calcium carbide CaC2. Lanthanides also form carbides with formula M2C3, metals from group 11 also tend to form acetylides, such as copper acetylide and silver acetylide. Carbides of the elements, which have stoichiometry MC2 and M2C3, are also described as salt-like derivatives of C22−. The C-C triple bond length ranges from 119.2 pm in CaC2, the bonding in LaC2 has been described in terms of LaIII with the extra electron delocalised into the antibonding orbital on C22−, explaining the metallic conduction. The polyatomic ion C34−, sometimes called sesquicarbide or allylenide, is found in Li4C3 and Mg2C3, the ion is linear and is isoelectronic with CO2. The C-C distance in Mg2C3 is 133.2 pm, Mg2C3 yields methylacetylene, CH3CCH, and propadiene, CH2CCH2, on hydrolysis, which was the first indication that it contains C34−. The carbides of silicon and boron are described as covalent carbides, silicon carbide has two similar crystalline forms, which are both related to the diamond structure. Boron carbide, B4C, on the hand, has an unusual structure which includes icosahedral boron units linked by carbon atoms. In this respect boron carbide is similar to the boron rich borides, both silicon carbide and boron carbide are very hard materials and refractory. Boron also forms other covalent carbides, e. g. B25C, the carbides of the group 4,5 and 6 transition metals are often described as interstitial compounds
6.
Carbonate
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In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, a polyatomic ion with the formula of CO2−3. The name may mean an ester of carbonic acid, an organic compound containing the carbonate group C2. In geology and mineralogy, the term carbonate can refer both to carbonate minerals and carbonate rock, and both are dominated by the ion, CO2−3. Carbonate minerals are extremely varied and ubiquitous in chemically precipitated sedimentary rock, sodium carbonate and potassium carbonate have been used since antiquity for cleaning and preservation, as well as for the manufacture of glass. Carbonates are widely used in industry, e. g. in iron smelting, as a raw material for Portland cement and lime manufacture, in the composition of ceramic glazes, the carbonate ion is the simplest oxocarbon anion. It consists of one carbon atom surrounded by three oxygen atoms, in a planar arrangement, with D3h molecular symmetry. It has a mass of 60.01 g/mol and carries a total formal charge of −2. It is the base of the hydrogen carbonate ion, HCO−3. The Lewis structure of the ion has two single bonds to negative oxygen atoms, and one short double bond to a neutral oxygen. This structure is incompatible with the symmetry of the ion. This process is called calcination, after calx, the Latin name of quicklime or calcium oxide, CaO, exceptions include lithium, sodium, potassium and ammonium carbonates, as well as many uranium carbonates. In aqueous solution, carbonate, bicarbonate, carbon dioxide, in strongly basic conditions, the carbonate ion predominates, while in weakly basic conditions, the bicarbonate ion is prevalent. In more acid conditions, aqueous carbon dioxide, CO2, is the main form, thus sodium carbonate is basic, sodium bicarbonate is weakly basic, while carbon dioxide itself is a weak acid. Carbonated water is formed by dissolving CO2 in water under pressure, in living systems an enzyme, carbonic anhydrase, speeds the interconversion of CO2 and carbonic acid. Although the carbonate salts of most metals are insoluble in water, in solution this equilibrium between carbonate, bicarbonate, carbon dioxide and carbonic acid changes consonant to changing temperature and pressure conditions. In the case of ions with insoluble carbonates, e. g. CaCO3. This is an explanation for the buildup of scale inside pipes caused by hard water, in organic chemistry a carbonate can also refer to a functional group within a larger molecule that contains a carbon atom bound to three oxygen atoms, one of which is double bonded. These compounds are known as organocarbonates or carbonate esters, and have the general formula ROCOOR′
7.
Oxide
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An oxide /ˈɒksaɪd/ is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. Oxide itself is the dianion of oxygen, an O2– atom, Metal oxides thus typically contain an anion of oxygen in the oxidation state of −2. Most of the Earths crust consists of oxides, the result of elements being oxidized by the oxygen in air or in water. Hydrocarbon combustion affords the two principal carbon oxides, carbon monoxide and carbon dioxide, even materials considered pure elements often develop an oxide coating. For example, aluminium foil develops a skin of Al2O3 that protects the foil from further corrosion. Individual elements can form multiple oxides, each containing different amounts of the element. Certain elements can form many different oxides, such those of nitrogen, due to its electronegativity, oxygen forms stable chemical bonds with almost all elements to give the corresponding oxides. Noble metals are prized because they resist direct chemical combination with oxygen, two independent pathways for corrosion of elements are hydrolysis and oxidation by oxygen. The combination of water and oxygen is even more corrosive, virtually all elements burn in an atmosphere of oxygen, or an oxygen rich environment. In the presence of water and oxygen, some elements— sodium—react rapidly, even dangerously, in part for this reason, alkali and alkaline earth metals are not found in nature in their metallic, i. e. native, form. Caesium is so reactive with oxygen that it is used as a getter in vacuum tubes, the surface of most metals consists of oxides and hydroxides in the presence of air. A well-known example is aluminium foil, which is coated with a film of aluminium oxide that passivates the metal. The aluminium oxide layer can be built to greater thickness by the process of electrolytic anodising, though solid magnesium and aluminium react slowly with oxygen at STP—they, like most metals, burn in air, generating very high temperatures. Finely grained powders of most metals can be explosive in air. Consequently, they are used in Solid-fuel rockets. In dry oxygen, iron forms iron oxide, but the formation of the hydrated ferric oxides, Fe2O3−x2x. Free oxygen production by photosynthetic bacteria some 3.5 billion years ago precipitated iron out of solution in the oceans as Fe2O3 in the important iron ore hematite. Oxides have a range of different structures, from molecules to polymeric
8.
Cyanide
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A cyanide is any chemical compound that contains monovalent combining group CN. This group, known as the group, consists of a carbon atom triple-bonded to a nitrogen atom. The cyanide ion is isoelectronic with carbon monoxide and with molecular nitrogen, organic cyanides are usually called nitriles, in these, the CN group is linked by a covalent bond to a carbon-containing group, such as methyl in methyl cyanide. Because they do not release cyanide ions, nitriles are generally toxic, or in the case of insoluble polymers such as acrylic fiber. Hydrocyanic acid, also known as hydrogen cyanide, or HCN, is a volatile liquid used to prepare acrylonitrile, which is used in the production of acrylic fibers, synthetic rubber. Cyanides are employed in a number of processes, including fumigation, case hardening of iron and steel, electroplating. In nature, substances yielding cyanide are present in seeds, such as the pit of the cherry. In IUPAC nomenclature, organic compounds that have a functional group are called nitriles. An example of a nitrile is CH3CN, acetonitrile, also known as methyl cyanide, nitriles usually do not release cyanide ions. A functional group with a hydroxyl and cyanide bonded to the carbon is called cyanohydrin. Unlike nitriles, cyanohydridins do release hydrogen cyanide, in inorganic chemistry, salts containing the C≡N− ion are referred to as cyanides. The word is derived from the Greek kyanos, meaning dark blue, cyanides are produced by certain bacteria, fungi, and algae and are found in a number of plants. Cyanides are found in substantial amounts in certain seeds and fruit stones, e. g. those of apricots, apples, in plants, cyanides are usually bound to sugar molecules in the form of cyanogenic glycosides and defend the plant against herbivores. Cassava roots, an important potato-like food grown in tropical countries, the Madagascar bamboo Cathariostachys madagascariensis produces cyanide as a deterrent to grazing. In response, the bamboo lemur, which eats the bamboo, has developed a high tolerance to cyanide. The cyanide radical CN· has been identified in interstellar space, the cyanide radical is used to measure the temperature of interstellar gas clouds. Hydrogen cyanide is produced by the combustion or pyrolysis of certain materials under oxygen-deficient conditions, for example, it can be detected in the exhaust of internal combustion engines and tobacco smoke. Certain plastics, especially derived from acrylonitrile, release hydrogen cyanide when heated or burnt
9.
Vitalism
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A Where vitalism explicitly invokes a vital principle, that element is often referred to as the vital spark, energy or élan vital, which some equate with the soul. Vitalism has a history in medical philosophies, most traditional healing practices posited that disease results from some imbalance in vital forces. In the Western tradition founded by Hippocrates, these forces were associated with the four temperaments and humours. One example of a notion in Africa is the Yoruba concept of ase. Today forms of vitalism continue to exist as philosophical positions or a tenet in many religious traditions, the notion that bodily functions are due to a vitalistic principle existing in all living creatures has roots going back at least to ancient Egypt. In Greek philosophy, the Milesian school proposed natural explanations deduced from materialism and mechanism, however, by the time of Lucretius, this account was supplemented, and in stoic physics, the pneuma assumed the role of logos. Galen believed the lungs draw pneuma from the air, which the blood communicates throughout the body and this debate was to persist throughout the ancient world. Atomistic mechanism got a shot in the arm from Epicurus, while the Stoics adopted a divine teleology. The choice seems simple, either show how a structured, regular world could arise out of undirected processes, in Europe, medieval physics was influenced by the idea of pneuma, helping to shape later aether theories. Jöns Jakob Berzelius, one of the early 19th century fathers of modern chemistry, vitalist chemists predicted that organic materials could not be synthesized from inorganic components, but Friedrich Wöhler synthesised urea from inorganic components in 1828. However, contemporary accounts do not support the belief that vitalism died when Wöhler made urea. Vitalism has long been regarded in the community as a corrupting pseudoscientific influence. Vitalism today is no longer philosophically and scientifically viable, and is used as a pejorative epithet. Ernst Mayr wrote, It would be ahistorical to ridicule vitalists, the logic of the critique of the vitalists was impeccable. Vitalism has become so disreputable a belief in the last fifty years that no biologist alive today would want to be classified as a vitalist. Still, the remnants of vitalist thinking can be found in the work of Alistair Hardy, Sewall Wright, and Charles Birch, louis Pasteur after his famous rebuttal of spontaneous generation, performed several experiments that he felt supported vitalism. According to Bechtel, Pasteur fitted fermentation into a general programme describing special reactions that only occur in living organisms. Rejecting the claims of Berzelius, Liebig, Traube and others that fermentation resulted from chemical agents or catalysts within cells, other vitalists included English anatomist Francis Glisson and the Italian doctor Marcello Malpighi
10.
Atomic theory
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In chemistry and physics, atomic theory is a scientific theory of the nature of matter, which states that matter is composed of discrete units called atoms. The word atom comes from the Ancient Greek adjective atomos, meaning indivisible, 19th century chemists began using the term in connection with the growing number of irreducible chemical elements. In fact, in extreme environments, such as neutron stars. Since atoms were found to be divisible, physicists later invented the term elementary particles to describe the uncuttable, though not indestructible, parts of an atom. The field of science which studies subatomic particles is particle physics, the idea that matter is made up of discrete units is a very old one, appearing in many ancient cultures such as Greece and India. However, these ideas were founded in philosophical and theological reasoning rather than evidence, because of this, they could not convince everybody, so atomism was but one of a number of competing theories on the nature of matter. Near the end of the 18th century, two laws about chemical reactions emerged without referring to the notion of an atomic theory. The first was the law of conservation of mass, formulated by Antoine Lavoisier in 1789, the second was the law of definite proportions. For example, Proust had studied tin oxides and found that their masses were either 88. 1% tin and 11. 9% oxygen or 78. 7% tin and 21. 3% oxygen. Dalton noted from these percentages that 100g of tin will combine either with 13. 5g or 27g of oxygen,13.5 and 27 form a ratio of 1,2, Dalton found that an atomic theory of matter could elegantly explain this common pattern in chemistry. In the case of Prousts tin oxides, one tin atom will combine with one or two oxygen atoms. Dalton hypothesized this was due to the differences in mass and complexity of the gases respective particles, indeed, carbon dioxide molecules are heavier and larger than nitrogen molecules. This marked the first truly scientific theory of the atom, since Dalton reached his conclusions by experimentation and examination of the results in an empirical fashion, in 1803 Dalton orally presented his first list of relative atomic weights for a number of substances. This paper was published in 1805, but he did not discuss there exactly how he obtained these figures, the method was first revealed in 1807 by his acquaintance Thomas Thomson, in the third edition of Thomsons textbook, A System of Chemistry. Finally, Dalton published an account in his own textbook. Dalton estimated the atomic weights according to the ratios in which they combined. However, Dalton did not conceive that with some elements atoms exist in molecules—e. g and he also mistakenly believed that the simplest compound between any two elements is always one atom of each. This, in addition to the crudity of his equipment, flawed his results, adopting better data, in 1806 he concluded that the atomic weight of oxygen must actually be 7 rather than 5.5, and he retained this weight for the rest of his life
11.
Chemical element
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A chemical element or element is a species of atoms having the same number of protons in their atomic nuclei. There are 118 elements that have identified, of which the first 94 occur naturally on Earth with the remaining 24 being synthetic elements. There are 80 elements that have at least one stable isotope and 38 that have exclusively radioactive isotopes, iron is the most abundant element making up Earth, while oxygen is the most common element in the Earths crust. Chemical elements constitute all of the matter of the universe. The two lightest elements, hydrogen and helium, were formed in the Big Bang and are the most common elements in the universe. The next three elements were formed mostly by cosmic ray spallation, and are rarer than those that follow. Formation of elements with from 6 to 26 protons occurred and continues to occur in main sequence stars via stellar nucleosynthesis, the high abundance of oxygen, silicon, and iron on Earth reflects their common production in such stars. The term element is used for atoms with a number of protons as well as for a pure chemical substance consisting of a single element. A single element can form multiple substances differing in their structure, when different elements are chemically combined, with the atoms held together by chemical bonds, they form chemical compounds. Only a minority of elements are found uncombined as relatively pure minerals, among the more common of such native elements are copper, silver, gold, carbon, and sulfur. All but a few of the most inert elements, such as gases and noble metals, are usually found on Earth in chemically combined form. While about 32 of the elements occur on Earth in native uncombined forms. For example, atmospheric air is primarily a mixture of nitrogen, oxygen, and argon, the history of the discovery and use of the elements began with primitive human societies that found native elements like carbon, sulfur, copper and gold. Later civilizations extracted elemental copper, tin, lead and iron from their ores by smelting, using charcoal, alchemists and chemists subsequently identified many more, almost all of the naturally occurring elements were known by 1900. Save for unstable radioactive elements with short half-lives, all of the elements are available industrially, almost all other elements found in nature were made by various natural methods of nucleosynthesis. On Earth, small amounts of new atoms are produced in nucleogenic reactions, or in cosmogenic processes. Of the 94 naturally occurring elements, those with atomic numbers 1 through 82 each have at least one stable isotope, Isotopes considered stable are those for which no radioactive decay has yet been observed. Elements with atomic numbers 83 through 94 are unstable to the point that radioactive decay of all isotopes can be detected, the very heaviest elements undergo radioactive decay with half-lives so short that they are not found in nature and must be synthesized
12.
Urea
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Urea, also known as carbamide, is an organic compound with the chemical formula CO2. This amide has two groups joined by a carbonyl functional group. Urea serves an important role in the metabolism of nitrogen-containing compounds by animals and is the main nitrogen-containing substance in the urine of mammals and it is a colorless, odorless solid, highly soluble in water, and practically non-toxic. Dissolved in water, it is neither acidic nor alkaline, the body uses it in many processes, most notably nitrogen excretion. The liver forms it by combining two molecules with a carbon dioxide molecule in the urea cycle. Urea is widely used in fertilizers as a source of nitrogen and is an important raw material for the chemical industry, Friedrich Wöhlers discovery in 1828 that urea can be produced from inorganic starting materials was an important conceptual milestone in chemistry. More than 90% of world production of urea is destined for use as a nitrogen-release fertilizer. Urea has the highest nitrogen content of all solid nitrogenous fertilizers in common use, therefore, it has the lowest transportation costs per unit of nitrogen nutrient. The standard crop-nutrient rating of urea is 46-0-0, many soil bacteria possess the enzyme urease, which catalyzes conversion of urea to ammonia or ammonium ion and bicarbonate ion. Thus urea fertilizers rapidly transform to the form in soils. Ammonium and nitrate are readily absorbed by plants, and are the dominant sources of nitrogen for plant growth, Urea is also used in many multi-component solid fertilizer formulations. Urea is highly soluble in water and is also very suitable for use in fertilizer solutions. For fertilizer use, granules are preferred over prills because of their particle size distribution. The most common impurity of synthetic urea is biuret, which impairs plant growth, Urea is usually spread at rates of between 40 and 300 kg/ha but rates vary. Smaller applications incur lower losses due to leaching, during summer, urea is often spread just before or during rain to minimize losses from volatilization. Because of the nitrogen concentration in urea, it is very important to achieve an even spread. The application equipment must be calibrated and properly used. Drilling must not occur on contact with or close to seed, Urea dissolves in water for application as a spray or through irrigation systems
13.
Salt (chemistry)
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In chemistry, a salt is an ionic compound that results from the neutralization reaction of an acid and a base. Salts are composed of related numbers of cations and anions so that the product is electrically neutral and these component ions can be inorganic, such as chloride, or organic, such as acetate, and can be monatomic, such as fluoride, or polyatomic, such as sulfate. There are several varieties of salts, salts that hydrolyze to produce hydroxide ions when dissolved in water are alkali salts, whilst those that hydrolyze to produce hydronium ions in water are acidic salts. Neutral salts are those salts that are neither acidic nor basic, zwitterions contain an anionic centre and a cationic centre in the same molecule, but are not considered to be salts. Examples of zwitterions include amino acids, many metabolites, peptides, usually, non-dissolved salts at standard conditions for temperature and pressure are solid, but there are exceptions. Molten salts and solutions containing dissolved salts are called electrolytes, as they are able to conduct electricity. As observed in the cytoplasm of cells, in blood, urine, plant saps and mineral waters, therefore, their salt content is given for the respective ions. Salts can appear to be clear and transparent, opaque, and even metallic, in many cases, the apparent opacity or transparency are only related to the difference in size of the individual monocrystals. Since light reflects from the boundaries, larger crystals tend to be transparent. The color of the salt is due to the electronic structure in the d-orbitals of transition elements or in the conjugated organic dye framework. Different salts can elicit all five basic tastes, e. g. salty, sweet, sour, bitter, and umami or savory. Salts of strong acids and strong bases are non-volatile and odorless and that slow, partial decomposition is usually accelerated by the presence of water, since hydrolysis is the other half of the reversible reaction equation of formation of weak salts. Many ionic compounds can be dissolved in water or other similar solvents, the exact combination of ions involved makes each compound have a unique solubility in any solvent. The solubility is dependent on how well each ion interacts with the solvent, for example, all salts of sodium, potassium and ammonium are soluble in water, as are all nitrates and many sulfates – barium sulfate, calcium sulfate and lead sulfate are examples of exceptions. However, ions that bind tightly to each other and form highly stable lattices are less soluble, for example, most carbonate salts are not soluble in water, such as lead carbonate and barium carbonate. Some soluble carbonate salts are, sodium carbonate, potassium carbonate, solid salts do not conduct electricity. Moreover, solutions of salts also conduct electricity, the name of a salt starts with the name of the cation followed by the name of the anion. Salts are often referred to only by the name of the cation or by the name of the anion. g
14.
Potassium cyanate
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Potassium cyanate is an inorganic compound with the formula KOCN. It is used to prepare many other compounds including useful herbicide, worldwide production of the potassium and sodium salts was 20,000 tons in 2006. Cyanate is isoelectronic with carbon dioxide and with azide, being linear, the C-N distance is 121 pm, about 5 pm longer than for cyanide. Potassium cyanate is isostructural with potassium azide, for most applications, the potassium and sodium salts can be used interchangeably. Potassium cyanate is often preferred to the salt, which is less soluble in water. Potassium cyanate is used as a raw material for various organic syntheses, including. For example, it is used to prepare the drug hydroxyurea and it is also used for the heat treatment of metals. Potassium Cyanate has been used to reduce the percentage of sickled erythrocytes under certain conditions and has increased the number of deformalities. In an aqueous solution, it has prevented irreversibly the in vitro sickling of hemoglobins containing human erythrocytes during deoxygenization, veterinarians have also found potassium cyanate useful in that the cyanate salts and isocyanates can treat parasite diseases in both birds and mammals. KOCN is prepared by heating urea with potassium carbonate at 400 °C,2 OC2 + K2CO3 →2 KOCN + 2CO3 The reaction produces a liquid. Intermediates and impurities include biuret, cyanuric acid, and potassium allophanate, as well as unreacted starting urea, protonation gives a 97,3 mixture of two tautomers, HNCO and NCOH. The more abundant tautomer trimerizes to cyanuric acid. This makes it easier to reach higher purities above 95%, another way to synthesize it is to allow an alkali metal, cyanide, to react with oxygen in nickel containers under controlled conditions. It can be formed by the oxidation of ferrocyanide, lastly, it can be made by heating potassium cyanide with lead oxide
15.
Ammonium sulfate
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Ammonium sulfate, 2SO4, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer and it contains 21% nitrogen and 24% sulphur. The primary use of ammonium sulfate is as a fertilizer for alkaline soils, in the soil the ammonium ion is released and forms a small amount of acid, lowering the pH balance of the soil, while contributing essential nitrogen for plant growth. The main disadvantage to the use of ammonium sulfate is its low nitrogen content relative to ammonium nitrate and it is also used as an agricultural spray adjuvant for water-soluble insecticides, herbicides, and fungicides. There, it functions to bind iron and calcium cations that are present in both water and plant cells. It is particularly effective as an adjuvant for 2, 4-D, glyphosate and this provides a convenient and simple means to fractionate complex protein mixtures. As such, ammonium sulfate is also listed as an ingredient for many United States vaccines per the Center for Disease Control, selective precipitation with ammonium sulfate, opposite to the usual precipitation technique which uses acetic acid, does not interfere with the determination of volatile fatty acids. As a food additive, ammonium sulfate is considered generally recognized as safe by the U. S. Food and Drug Administration and it is used as an acidity regulator in flours and breads. Ammonium sulfate is used on a scale in the preparation of other ammonium salts. A saturated solution of ammonium sulfate in water is used as an external standard in sulfur NMR spectroscopy with shift value of 0 ppm. Ammonium sulfate has also used in flame retardant compositions acting much like diammonium phosphate. As a flame retardant, it increases the temperature of the material, decreases maximum weight loss rates. Its flame retardant efficacy can be enhanced by blending it with ammonium sulfamate, concentrated sulfuric acid is added to keep the solution acidic, and to retain its level of free acid. The heat of reaction keeps reactor temperature at 60 °C, dry, powdered ammonium sulfate may be formed by spraying sulfuric acid into a reaction chamber filled with ammonia gas. The heat of reaction evaporates all water present in the system, approximately 6000M tons were produced in 1981. Ammonium sulfate also is manufactured from gypsum, finely divided gypsum is added to an ammonium carbonate solution. Calcium carbonate precipitates as a solid, leaving ammonium sulfate in the solution, 2CO3 + CaSO4 → 2SO4 + CaCO3 Ammonium sulfate occurs naturally as the rare mineral mascagnite in volcanic fumaroles and due to coal fires on some dumps. Ammonium sulfate becomes ferroelectric at temperatures below -49.5 °C, at room temperature it crystallises in the orthorhombic system, with cell sizes of a =7.729 Å, b =10.560 Å, c =5.951 Å
16.
Isoleucine
–
Isoleucine encoded by the codons ATT, ATC, ATA is an α-amino acid that is used in the biosynthesis of proteins. It contains a group, an α-carboxylic acid group. It is essential in humans, meaning the body cannot synthesize it, Isoleucine is synthesized from pyruvate employing leucine biosynthesis enzymes in other organisms such as bacteria. However, in cases, MSUD can lead to damage to the brain cells. As an essential nutrient, it is not synthesized in the body, hence it must be ingested, in plants and microorganisms, it is synthesized via several steps, starting from pyruvic acid and alpha-ketoglutarate. It can also be converted into Acetyl CoA and fed into the TCA cycle by condensing with oxaloacetate to form citrate, in mammals Acetyl CoA cannot be converted back to carbohydrate but can be used in the synthesis of ketone bodies or fatty acids, hence ketogenic. Biotin, sometimes referred to as Vitamin B7 or Vitamin H, is a requirement for the full catabolism of isoleucine. Without adequate biotin, the body will be unable to fully break down isoleucine and leucine molecules. Even though this acid is not produced in animals, it is stored in high quantities. Foods that have high amounts of isoleucine include eggs, soy protein, seaweed, turkey, chicken, lamb, cheese, Isoleucine can be synthesized in a multistep procedure starting from 2-bromobutane and diethylmalonate. Synthetic isoleucine was originally reported in 1905, german chemist Felix Ehrlich discovered isoleucine in hemoglobin in 1903. Center for Biological Sequence Analysis, University of Denmark http, //www. cbs. dtu. dk/courses/27619/codon. html Isoleucine and valine biosynthesis
17.
Alloy
–
An alloy is a mixture of metals or a mixture of a metal and another element. Alloys are defined by a metallic bonding character, an alloy may be a solid solution of metal elements or a mixture of metallic phases. Intermetallic compounds are alloys with a stoichiometry and crystal structure. Zintl phases are sometimes considered alloys depending on bond types. Alloys are used in a variety of applications. In some cases, a combination of metals may reduce the overall cost of the material while preserving important properties, in other cases, the combination of metals imparts synergistic properties to the constituent metal elements such as corrosion resistance or mechanical strength. Examples of alloys are steel, solder, brass, pewter, duralumin, bronze, the alloy constituents are usually measured by mass. Alloys are usually classified as substitutional or interstitial alloys, depending on the arrangement that forms the alloy. They can be classified as homogeneous, or heterogeneous or intermetallic. An alloy is a mixture of elements, which forms an impure substance that retains the characteristics of a metal. Alloys are made by mixing two or more elements, at least one of which is a metal and this is usually called the primary metal or the base metal, and the name of this metal may also be the name of the alloy. The other constituents may or may not be metals but, when mixed with the base, they will be soluble. The mechanical properties of alloys will often be different from those of its individual constituents. A metal that is very soft, such as aluminium, can be altered by alloying it with another soft metal. Although both metals are soft and ductile, the resulting aluminium alloy will have much greater strength. Adding a small amount of carbon to iron trades its great ductility for the greater strength of an alloy called steel. Due to its strength, but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful. By adding chromium to steel, its resistance to corrosion can be enhanced, creating stainless steel, while adding silicon will alter its electrical characteristics, producing silicon steel
18.
Steel
–
Steel is an alloy of iron and other elements, primarily carbon, that is widely used in construction and other applications because of its high tensile strength and low cost. Steels base metal is iron, which is able to take on two forms, body centered cubic and face centered cubic, depending on its temperature. It is the interaction of those allotropes with the elements, primarily carbon. In the body-centred cubic arrangement, there is an atom in the centre of each cube. Carbon, other elements, and inclusions within iron act as hardening agents that prevent the movement of dislocations that otherwise occur in the lattices of iron atoms. The carbon in steel alloys may contribute up to 2. 1% of its weight. Steels strength compared to pure iron is possible at the expense of irons ductility. With the invention of the Bessemer process in the mid-19th century and this was followed by Siemens-Martin process and then Gilchrist-Thomas process that refined the quality of steel. With their introductions, mild steel replaced wrought iron, further refinements in the process, such as basic oxygen steelmaking, largely replaced earlier methods by further lowering the cost of production and increasing the quality of the product. Today, steel is one of the most common materials in the world and it is a major component in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons. Modern steel is generally identified by various grades defined by assorted standards organizations, the noun steel originates from the Proto-Germanic adjective stakhlijan, which is related to stakhla. The carbon content of steel is between 0. 002% and 2. 1% by weight for plain iron–carbon alloys and these values vary depending on alloying elements such as manganese, chromium, nickel, iron, tungsten, carbon and so on. Basically, steel is an alloy that does not undergo eutectic reaction. In contrast, cast iron does undergo eutectic reaction, too little carbon content leaves iron quite soft, ductile, and weak. Carbon contents higher than those of steel make an alloy, commonly called pig iron, while iron alloyed with carbon is called carbon steel, alloy steel is steel to which other alloying elements have been intentionally added to modify the characteristics of steel. Common alloying elements include, manganese, nickel, chromium, molybdenum, boron, titanium, vanadium, tungsten, cobalt, and niobium. Additional elements are important in steel, phosphorus, sulfur, silicon, and traces of oxygen, nitrogen, and copper. Alloys with a higher than 2. 1% carbon content, depending on other element content, cast iron is not malleable even when hot, but it can be formed by casting as it has a lower melting point than steel and good castability properties
19.
Cementite
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Cementite, also known as iron carbide, is an intermetallic compound of iron and carbon, more precisely an intermediate transition metal carbide with the formula Fe3C. By weight, it is 6. 67% carbon and 93. 3% iron and it has an orthorhombic crystal structure. It is a hard, brittle material, normally classified as a ceramic in its pure form, therefore, in carbon steels and cast irons that are slowly cooled, a portion of the carbon is in the form of cementite. Cementite forms directly from the melt in the case of white cast iron, in carbon steel, cementite precipitates from austenite as austenite transforms to ferrite on slow cooling, or from martensite during tempering. An intimate mixture with ferrite, the product of austenite. Cementite changes from ferromagnetic to paramagnetic at its Curie temperature of approximately 480 K, a natural iron carbide occurs in iron meteorites and is called cohenite after the German mineralogist Emil Cohen, who first described it. The figure shows the behaviour at room temperature. There are other forms of iron carbides that have been identified in tempered steel. These include Epsilon carbide, hexagonal close-packed Fe2-3C, precipitates in plain-carbon steels of carbon content >0. 2%, non-stoichiometric ε-carbide dissolves above ~200 °C, where Hägg carbides and cementite begin to form. Hägg carbide, monoclinic Fe5C2, precipitates in hardened tool steels tempered at 200-300 °C, characterization of different iron carbides is not at all a trivial task, and often X-ray diffraction is complemented by Mössbauer spectroscopy. Foundations of Materials Science and Engineering, microstructure of Steels and Cast Irons. Ester Esna du Plessis The Crystal Structures of Iron Carbides, Ph. D, formation of Fe7C3 and Fe5C2 type metastable carbides during the crystallization of an amorphous Fe75C25 alloy
20.
Calcium carbide
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Calcium carbide is a chemical compound with the chemical formula of CaC2. Its main use industrially is in the production of acetylene and calcium cyanamide, the pure material is colorless, however pieces of technical-grade calcium carbide are grey or brown and consist of about 80–85% of CaC2. In the presence of moisture, technical-grade calcium carbide emits an unpleasant odor reminiscent of garlic. Applications of calcium carbide include manufacture of gas, and for generation of acetylene in carbide lamps, manufacture of chemicals for fertilizer. Calcium carbide is produced industrially in an arc furnace from a mixture of lime. The carbide product produced generally contains around 80% calcium carbide by weight, the carbide is crushed to produce small lumps that can range from a few mm up to 50 mm. The impurities are concentrated in the finer fractions, the CaC2 content of the product is assayed by measuring the amount of acetylene produced on hydrolysis. As an example, the British and German standards for the content of the fractions are 295 L/kg and 300 L/kg respectively. Impurities present in the carbide include phosphide, which produces phosphine when hydrolysed, the method for the production in an electric arc furnace was discovered in 1892 by T. L Willson and independently by H. Moissan in the same year. Pure calcium carbide is a colourless solid, the common crystalline form at room temperature is a distorted rock-salt structure with the C22− units lying parallel. The reaction of carbide with water, producing acetylene and calcium hydroxide, was discovered by Friedrich Wöhler in 1862. CaC2 +2 H2O → C2H2 + Ca2 This reaction was the basis of the manufacture of acetylene. At high temperatures, CaC2 reacts with water vapor to give calcium carbonate, carbon dioxide, today acetylene is mainly manufactured by the partial combustion of methane or appears as a side product in the ethylene stream from cracking of hydrocarbons. Approximately 400,000 tonnes are produced this way annually, in China, acetylene derived from calcium carbide remains a raw material for the chemical industry, in particular for the production of polyvinyl chloride. Locally produced acetylene is more economical than using imported oil, production of calcium carbide in China has been increasing. In 2005 output was 8.94 million tons, with the capacity to produce 17 million tons, in the USA, Europe, and Japan, consumption of calcium carbide is generally declining. Production levels in the USA in 1990s were 236,000 tons per year, Calcium carbide reacts with nitrogen at high temperature to form calcium cyanamide, CaC2 + N2 → CaCN2 + C Commonly known as nitrolim, calcium cyanamide is used as fertilizer. It is hydrolysed to cyanamide, H2NCN, Calcium carbide is used, in the desulfurisation of iron as a fuel in steelmaking to extend the scrap ratio to liquid iron, depending on economics
21.
Graphite intercalation compound
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Graphite intercalation compounds are complex materials having a formula CXm where the ion Xn+ or Xn− is inserted between the oppositely charged carbon layers. Typically m is less than 1. These materials are deeply colored solids that exhibit a range of electrical and these materials are prepared by treating graphite with a strong oxidant or a strong reducing agent, C + m X → CXm The reaction is reversible. The host and the guest X interact by charge transfer, a analogous process is the basis of commercial lithium-ion batteries. In a graphite intercalation compound not every layer is necessarily occupied by guests, in so-called stage 1 compounds, graphite layers and intercalated layers alternate and in stage 2 compounds, two graphite layers with no guest material in between alternate with an intercalated layer. The actual composition may vary and therefore these compounds are an example of non-stoichiometric compounds and it is customary to specify the composition together with the stage. The layers are pushed apart upon incorporation of the guest ions, one of the best studied graphite intercalation compounds, KC8, is prepared by melting potassium over graphite powder. The potassium is absorbed into the graphite and the material changes color from black to bronze, the composition is explained by assuming that the potassium to potassium distance is twice the distance between hexagons in the carbon framework. The bond between anionic graphite layers and potassium cations is ionic, the electrical conductivity of the material is greater than that of α-graphite. KC8 is a superconductor with a low critical temperature Tc =0.14 K. The stoichiometry MC8 is observed for M = K, Rb, for smaller ions M = Li+, Sr2+, Ba2+, Eu2+, Yb3+, and Ca2+, the limiting stoichiometry is MC6. Calcium graphite CaC6 is obtained by immersing highly oriented pyrolytic graphite in liquid Li–Ca alloy for 10 days at 350 °C, the crystal structure of CaC6 belongs to the R3m space group. The graphite interlayer distance increases upon Ca intercalation from 3.35 to 4.524 Å, with barium and ammonia, the cations are solvated, giving the stoichiometry or those with caesium, hydrogen and potassium. Interestingly, different from other metals, the amount of Na intercalation is very small. The phenomenon arises from the competition between trends in the energy and the ion–substrate coupling, down the columns of the periodic table. However, considerable Na intercalation into graphite can occur in cases when the ion is wrapped in a solvent shell through the process of co-intercalation, Na ions can intercalate into graphite when using certain glyme based electrolytes. Co-intercalation using glyme electrolytes can also facilitate faster potassium ion intercalation into graphite, the intercalation compounds graphite bisulfate and graphite perchlorate can be prepared by treating graphite with strong oxidizing agents in the presence of strong acids. Cathodic reduction of graphite perchlorate is analogous to heating KC8, which leads to an elimination of HClO4
22.
Allotropy
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Allotropy or allotropism is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of these elements. Allotropes are different structural modifications of an element, the atoms of the element are bonded together in a different manner, for example, the allotropes of carbon include diamond, graphite, graphene, and fullerenes. The term allotropy is used for only, not for compounds. The more general term, used for any material, is polymorphism. Allotropy refers only to different forms of an element within the same phase, for some elements, allotropes have different molecular formulae which can persist in different phases – for example, two allotropes of oxygen, can both exist in the solid, liquid and gaseous states. The concepts of allotropy was originally proposed in 1841 by the Swedish scientist Baron Jöns Jakob Berzelius, the term is derived from Greek άλλοτροπἱα, meaning variability, changeableness. After the acceptance of Avogadros hypothesis in 1860 it was understood that elements could exist as molecules. In the early 20th century it was recognized that other such as carbon were due to differences in crystal structure. Although many other chemists have repeated this advice, IUPAC and most chemistry texts still favour the usage of allotrope, allotropes are different structural forms of the same element and can exhibit quite different physical properties and chemical behaviours. The change between allotropic forms is triggered by the forces that affect other structures, i. e. pressure, light. Therefore, the stability of the particular allotropes depends on particular conditions.2 °C, as an example of allotropes having different chemical behaviour, ozone is a much stronger oxidizing agent than dioxygen. Typically, elements capable of variable coordination number and/or oxidation states tend to exhibit greater numbers of allotropic forms, another contributing factor is the ability of an element to catenate. Cerium, samarium, dysprosium and ytterbium have three allotropes, praseodymium, neodymium, gadolinium and terbium have two allotropes. Plutonium has six distinct solid allotropes under normal pressures and their densities vary within a ratio of some 4,3, which vastly complicates all kinds of work with the metal. A seventh plutonium allotrope exists at high pressures. The transuranium metals Np, Am, and Cm are also allotropic, promethium, americium, berkelium and californium have three allotropes each. Isomer Polymorphism Superdense carbon allotropes Chisholm, Hugh, ed. Allotropy
23.
Cyanides
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A cyanide is any chemical compound that contains monovalent combining group CN. This group, known as the group, consists of a carbon atom triple-bonded to a nitrogen atom. The cyanide ion is isoelectronic with carbon monoxide and with molecular nitrogen, organic cyanides are usually called nitriles, in these, the CN group is linked by a covalent bond to a carbon-containing group, such as methyl in methyl cyanide. Because they do not release cyanide ions, nitriles are generally toxic, or in the case of insoluble polymers such as acrylic fiber. Hydrocyanic acid, also known as hydrogen cyanide, or HCN, is a volatile liquid used to prepare acrylonitrile, which is used in the production of acrylic fibers, synthetic rubber. Cyanides are employed in a number of processes, including fumigation, case hardening of iron and steel, electroplating. In nature, substances yielding cyanide are present in seeds, such as the pit of the cherry. In IUPAC nomenclature, organic compounds that have a functional group are called nitriles. An example of a nitrile is CH3CN, acetonitrile, also known as methyl cyanide, nitriles usually do not release cyanide ions. A functional group with a hydroxyl and cyanide bonded to the carbon is called cyanohydrin. Unlike nitriles, cyanohydridins do release hydrogen cyanide, in inorganic chemistry, salts containing the C≡N− ion are referred to as cyanides. The word is derived from the Greek kyanos, meaning dark blue, cyanides are produced by certain bacteria, fungi, and algae and are found in a number of plants. Cyanides are found in substantial amounts in certain seeds and fruit stones, e. g. those of apricots, apples, in plants, cyanides are usually bound to sugar molecules in the form of cyanogenic glycosides and defend the plant against herbivores. Cassava roots, an important potato-like food grown in tropical countries, the Madagascar bamboo Cathariostachys madagascariensis produces cyanide as a deterrent to grazing. In response, the bamboo lemur, which eats the bamboo, has developed a high tolerance to cyanide. The cyanide radical CN· has been identified in interstellar space, the cyanide radical is used to measure the temperature of interstellar gas clouds. Hydrogen cyanide is produced by the combustion or pyrolysis of certain materials under oxygen-deficient conditions, for example, it can be detected in the exhaust of internal combustion engines and tobacco smoke. Certain plastics, especially derived from acrylonitrile, release hydrogen cyanide when heated or burnt
24.
Phosphaalkyne
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In chemistry, phosphaalkynes are organophosphorus compounds that have a phosphorus-carbon triple bond. Two types of phosphaalkynes are recognized, one type of phosphaalkyne is a heavier analogue of nitriles, i. e. P replaces N in a nitrile. Another type of phosphaalkyne feature pentavalent, three coordinate phosphorus, such species can also be described as ylides or phosphinocarbenes. The phosphorus version of the isonitriles R-P+≡C−, which would be called isophosphaalkynes, has not been observed, in 1950, H. Albers reported the first indication of the existence of the parent compound of phosphaalkynes, H-C≡P. This compound was identified by infrared absorption spectrometry, and its synthesis was improved by Manfred Regitz in 1987, the synthesis of the first kinetically stable phosphaalkyne, which has a tert-butyl group as a substituent R, was reported in 1981 by Gerd Becker and Werner Uhl. These phosphaalkynes undergo 1, 2-addition reactions and cycloadditions, in 2000, Guy Bertrand reported the first structure of the type B phosphaalkyne. Its P-C-R bond angle is 152.6 degrees, so this type of phosphaalkyne may be best described by a phosphorus vinyl ylide structure, the cyaphide ion P≡C− as the phosphorus cyanide cousin is not known as a salt and only observed in the gas phase. In silico measurements reveal that the -1 charge in this ion is mainly on carbon. On the other hand, the molecule does exist as a ligand in the ruthenium transition metal complex trans-. Recently, the synthesis and electronic structure of the first cyaphide-alkynyl complexes has been reported, the novel complexes trans- are the first complexes to incorporate cyaphide as part of a conjugated system
25.
Carbon disulfide
–
Carbon disulfide is a colorless volatile liquid with the formula CS2. The compound is used frequently as a block in organic chemistry as well as an industrial and chemical non-polar solvent. It has an odor, but commercial samples are typically contaminated with foul-smelling impurities. Small amounts of carbon disulfide are released by volcanic eruptions and marshes, CS2 once was manufactured by combining carbon and sulfur at high temperatures. It is isoelectronic with carbon dioxide, united States production in 2007 was 56,000 tonnes. Carbon disulfide is a solvent for phosphorus, sulfur, selenium, bromine, iodine, fats, resins, rubber and it has been used in the purification of single-walled carbon nanotubes. Compared to CO2, CS2 is more reactive toward nucleophiles and more easily reduced and these differences in reactivity can be attributed to the weaker π donor-ability of the sulfido centers, which renders the carbon more electrophilic. Both xanthates and the related thioxanthates are used as agents in mineral processing. Sodium sulfide affords trithiocarbonate, Na2S + CS2 →2 Carbon disulfide does not hydrolyze readily, chlorination of CS2 is the principal route to carbon tetrachloride, CS2 +3 Cl2 → CCl4 + S2Cl2 This conversion proceeds via the intermediacy of thiophosgene, CSCl2. CS2 is a ligand for metal complexes, forming pi complexes. CS2 polymerizes upon photolysis or under pressure to give an insoluble material called Bridgmans black, named after the discoverer of the polymer. Trithiocarbonate linkages comprise, in part, the backbone of the polymer, the principal industrial uses of carbon disulfide, consuming 75% of the annual production are the manufacture of viscose rayon, cellophane film. It is also an intermediate in chemical synthesis of carbon tetrachloride. It is widely used in the synthesis of compounds such as metam sodium, xanthates, dithiocarbamates. It can be used in fumigation of airtight storage warehouses, airtight flat storages, bins, grain elevators, railroad box cars, shipholds, barges and cereal mills. Carbon disulfide is used as an insecticide for the fumigation of grains, nursery stock, in fresh fruit conservation and as a soil disinfectant against insects. Typical recommended TLV is 30 mg/m3,10 ppm, symptoms include tingling or numbness, cramps, muscle weakness, pain, distal sensory loss, and neurophysiological impairment
26.
Phosgene
–
Phosgene is the chemical compound with the formula COCl2. This colorless gas gained infamy as a weapon during World War I where it was responsible for about 85% of the 100,000 deaths caused by chemical weapons. It is also a valued industrial reagent and building block in synthesis of pharmaceuticals, in low concentrations, its odor resembles freshly cut hay or grass. In addition to its production, small amounts occur from the breakdown. The chemical was named by combining the Greek words phos and genesis, Phosgene is a planar molecule as predicted by VSEPR theory. The C=O distance is 1.18 Å, the C−Cl distance is 1.74 Å and it is one of the simplest acid chlorides, being formally derived from carbonic acid. Typically, the reaction is conducted between 50 and 150 °C, above 200 °C, phosgene reverts to carbon monoxide and chlorine, Keq =0.05. World production of this compound was estimated to be 2.74 million tonnes in 1989, because of safety issues, phosgene is often produced and consumed within the same plant, and extraordinary measures are made to contain this toxic gas. It is listed on schedule 3 of the Chemical Weapons Convention, upon ultraviolet radiation in the presence of oxygen, chloroform slowly converts into phosgene by a radical reaction. To suppress this photodegradation, chloroform is often stored in brown-tinted glass containers, chlorinated compounds used to remove oil from metals, such as automotive brake cleaners, are converted to phosgene by the UV rays of arc welding processes. Phosgene may also be produced during testing for leaks of older-style refrigerant gases, chloromethanes were formerly leak-tested in situ by employing a small gas torch with a sniffer tube and a copper reaction plate in the flame nozzle of the torch. If any refrigerant gas was leaking from a pipe or joint, in the process, phosgene gas would be created due to the thermal reaction. Electronic sensing of refrigerant gases phased out the use of testing for leaks in the 1980s. Phosgene can be released during building fires, in one instance, a deputy fire chief was killed ten days after inhaling fumes that wafted down outside a burning restaurant. After a two-day hospitalization he had appeared to recover, but ultimately suffered cardiac arrest at home following from tracheobronchial inflammation, alveolar hemorrhage, the phosgene was produced by decomposing freon-22 after flames ducted up from a grease fire heated an air-conditioning unit on the roof and ruptured a hose. The great majority of phosgene is used in the production of isocyanates and these two isocyanates are precursors to polyurethanes. In the research laboratory phosgene still finds limited use in organic synthesis, a variety of substitutes have been developed, notably trichloromethyl chloroformate, a liquid at room temperature, and bis carbonate, a crystalline substance. Thionyl chloride is commonly and more safely employed for this application
27.
Carborane
–
A carborane is a cluster composed of boron, carbon and hydrogen atoms. Carboranes are an example of heteroboranes. Interesting examples of carboranes are the extremely stable icosahedral closo-carboranes, the electronic structure of these compounds is best described by Wade-Mingos rules for cluster molecules. Another important carborane is carborane acid, a chlorinated superacid H, the most heavily studied carborane is C2B10H12, m. p.320 °C. It is often prepared from the reaction of acetylene with decaborane, a variation on this method entails the use of dimethyl acetylenedicarboxylate to give C2B10H102, which can be degraded to the C2B10H12. Heretofore, decaborane derivatives were thought to be unstable and reactive with air. Ortho dicarborane is the product from the addition of acetylenes to decarborane precursors. Upon heating at 420 °C, the ortho dicarborane rearranges to the meta isomer, upon further heating, one obtains para-carborane. Like arenes, carboranes also undergo electrophilic aromatic substitution, numerous studies have been made on derivatives of the so-called dicarbollide anion, 2−. The first metal dicarbollide complex was discovered by M. Frederick Hawthorne and this anion forms sandwich compounds, referred to as bis, with many metal ions and some exist in otherwise unusual oxidation states. The dianion is a nido cluster prepared by degradation of the parent dicarborane, for example, Ni-based bis cluster can be observed for the rare Ni oxidation state of nickel. Carboryne, or 1, 2-dehydro-o-carborane, is a derivative of ortho-carborane with the formula B10C2H10. The hydrogen atoms on the C2 unit in the parent o-carborane are missing, the compound resembles and is isolobal with benzyne. A carboryne compound was first generated in 1990 starting from o-carborane, the hydrogen atoms connected to carbon are removed by n-butyllithium in tetrahydrofuran and the resulting lithium dianion is reacted with bromine at 0 °C to form the bromo monoanion. Heating the reaction mixture to 35 °C releases carboryne, which can subsequently be trapped with suitable dienes, such as anthracene, carborynes react with alkynes to benzocarboranes in an adaptation of the above described procedure. O-carborane is deprotonated with n-butyllithium as before and then reacted with nickel to a nickel coordinated carboryne. This compound reacts with 3-hexyne in an alkyne trimerization to the benzocarborane, single crystal X-ray diffraction analysis of this compound shows considerable bond length alternation in the benzene ring ruling out aromaticity. Carboranes have been explored as a source of boron in boron capture therapy
28.
Metal carbonyl
–
Metal carbonyls are coordination complexes of transition metals with carbon monoxide ligands. Metal carbonyls are useful in synthesis and as catalysts or catalyst precursors in homogeneous catalysis, such as hydroformylation. In the Mond process, nickel carbonyl is used to produce pure nickel, in organometallic chemistry, metal carbonyls serve as precursors for the preparation of other organometalic complexes. Metal carbonyls are toxic by skin contact, inhalation or ingestion, in part because of their ability to carbonylate hemoglobin to give carboxyhemoglobin, which prevents the binding of O2. The nomenclature of the metal carbonyls depends on the charge of the complex, the number and type of atoms. They occur as neutral complexes, as positively charged metal cations or as negatively charged metal carbonylates. The carbon monoxide ligand may be bound terminally to a metal atom or bridging to two or more metal atoms. These complexes may be homoleptic, that is containing only CO ligands, such as nickel carbonyl, mononuclear metal carbonyls contain only one metal atom as the central atom. Except vanadium hexacarbonyl only metals with even number such as chromium, iron, nickel. Polynuclear metal carbonyls are formed from metals with odd order numbers, complexes with different metals, but only one type of ligand will be referred to as isoleptic. The number of carbon monoxide ligands in a metal carbonyl complex is described by a Greek numeral, Carbon monoxide has different binding modes in metal carbonyls. They differ in the hapticity and the bridging mode, the hapticity describes the number of carbon monoxide ligands, which are directly bonded to the central atom. The denomination shall be made by the letter ηn, which is prefixed to the name of the complex, the superscript n indicates the number of bounded atoms. In monohapto coordination, such as in terminally bonded carbon monoxide, If carbon monoxide is bound via the carbon atom and via the oxygen to the metal, it will be referred to as dihapto coordinated η2. The carbonyl ligand engages in a range of bonding modes in metal carbonyl dimers and clusters, in the most common bridging mode, the CO ligand bridges a pair of metals. This bonding mode is observed in the available metal carbonyls, Co28, Fe29, Fe312. In certain higher nuclearity clusters, CO bridges between three or even four metals and these ligands are denoted μ3-CO and μ4-CO. Less common are bonding modes in which both C and O bond to the metal, e. g. μ3-η2, Carbon monoxide bonds to transition metals using synergistic π* back-bonding
29.
Mellitic anhydride
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Mellitic anhydride, the anhydride of mellitic acid, is an organic compound with the formula C12O9. Mellitic anhydride is an oxide of carbon, like CO2, CO and it is a white sublimable solid, apparently obtained by Liebig and Wöhler in 1830 in their study of mellite, they assigned it the empiric formula C4O3. The substance was characterized in 1913 by H. Meyer. It retains the character of the benzene ring
30.
Oxocarbon
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An oxocarbon or oxide of carbon is a chemical compound consisting only of carbon and oxygen. The simplest and most common oxocarbons are carbon monoxide and carbon dioxide, many other stable or metastable oxides of carbon are known, but they are rarely encountered, such as carbon suboxide and mellitic anhydride. While textbooks will often list only the first three, and rarely the fourth, a number of other oxides are known today. Some of these new oxides are stable at room temperature, some are metastable or stable only at very low temperatures, but decompose to simpler oxocarbons when warmed. The inventory of oxocarbons appears to be steadily growing, the existence of graphene oxide and of other stable polymeric carbon oxides with unbounded molecular structures suggests that many more remain to be discovered. It was gradually recognized as a substance, formerly called spiritus sylvestre or fixed air. Carbon monoxide may occur in combustion, too, and was used since antiquity for the smelting of iron from its ores, like the dioxide, it was described and studied in the West by various alchemists and chemists since the Middle Ages. Its true composition was discovered by William Cruikshank in 1800, carbon suboxide was discovered by Brodie in 1873, by passing electric current through carbon dioxide. The fourth classical oxide, mellitic anhydride, was obtained by Liebig and Wöhler in 1830 in their study of mellite. Some of these reactive carbon oxides were detected within molecular clouds in the medium by rotational spectroscopy. Many hypothetical oxocarbons have been studied by theoretical methods but have yet to be detected, normally, carbon is tetravalent, while oxygen is divalent, and in most oxocarbons each carbon atom may be bound to four other atoms, while oxygen may be bound to at most two. Moreover, while carbon can connect to other carbons to form arbitrarily large chains or networks, thus the known electrically neutral oxocarbons generally consist of one or more carbon skeletons connected and terminated by oxide or peroxide groups. Carbon atoms with unsatisfied bonds are found in oxides, such as the diradical C2O or, C=C=O. Loss or gain of electrons can result in monovalent negative oxygen, trivalent positive oxygen, the last two are found in carbon monoxide, −C≡O+. Negative oxygen occurs in most oxocarbon anions. One family of carbon oxides has the general formula CnO2, or O=nO — namely, the first members are CO2 or O=C=O, the well-known carbon dioxide. C2O2 or O=C=C=O, the extremely unstable ethylene dione, C3O2 or O=C=C=C=O, the metastable carbon suboxide or tricarbon dioxide. C4O2 or O=C=C=C=C=O, tetracarbon dioxide or 1,2, 3-Butatriene-1, 4-dione C5O2 or O=C=C=C=C=C=O, pentacarbon dioxide, stable in solution at room temp. and pure up to −90 °C. Some higher members of family have been detected in trace amounts in low-pressure gas phase and/or cryogenic matrix experiments, specifically for n =7 and n =17,19
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Nickel tetracarbonyl
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Nickel carbonyl is the organonickel compound with the formula Ni4. This pale-yellow liquid is the carbonyl of nickel. It is an intermediate in the Mond process for the purification of nickel, Nickel carbonyl is one of the most toxic substances encountered in industrial processes. In nickel tetracarbonyl, the state for nickel is assigned as zero. The formula conforms to 18-electron rule, the molecule is tetrahedral, with four carbonyl ligands attached to nickel. The CO ligands, in which the C and the O are connected by bonds, are covalently bonded to the nickel atom via the carbon ends. Electron diffraction studies have been performed on this molecule, and the Ni–C, Ni4 was first synthesised in 1890 by Ludwig Mond by the direct reaction of nickel metal with CO. This pioneering work foreshadowed the existence of other metal carbonyl compounds, including those of V, Cr, Mn, Fe. It was also applied industrially to the purification of nickel by the end of the 19th century, at 323 K, carbon monoxide is passed over impure nickel. The optimal rate occurs at 130 °C, Ni4 is not readily available commercially. It is conveniently generated in the laboratory by carbonylation of commercially available bisnickel, on moderate heating, Ni4 decomposes to carbon monoxide and nickel metal. Combined with the formation from CO and even impure nickel. Thermal decomposition commences near 180 °C and increases at higher temperature, like other low-valent metal carbonyls, Ni4 is susceptible to attack by nucleophiles. Attack can occur at nickel center, resulting in displacement of CO ligands, or at CO. Thus, donor ligands such as triphenylphosphine react to give Ni3, bipyridine and related ligands behave similarly. The monosubstitution of nickel tetracarbonyl with other ligands can be used to determine the Tolman electronic parameter, treatment with hydroxides gives clusters such as 2− and 2−. These compounds can also be obtained by reduction of nickel carbonyl, Thus, treatment of Ni4 with carbon nucleophiles results in acyl derivatives such as −. Chlorine oxidizes nickel carbonyl into NiCl2, releasing CO gas and this reaction provides a convenient method for destroying unwanted portions of the toxic compound. Reactions of Ni4 with alkyl and aryl halides often result in carbonylated organic products, vinylic halides, such as PhCH=CHBr, are converted to the unsaturated esters upon treatment with Ni4 followed by sodium methoxide
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Organometallic chemistry
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Moreover, some related compounds such as transition metal hydrides and metal phosphine complexes are often included in discussions of organometallic compounds. The field of organometallic chemistry combines aspects of inorganic and organic chemistry. Organometallic compounds are distinguished by the prefix organo- e. g. organopalladium compounds, examples of such organometallic compounds include all Gilman reagents, which contain lithium and copper. Tetracarbonyl nickel, and ferrocene are examples of compounds containing transition metals. The term metalorganics usually refers to metal-containing compounds lacking direct metal-carbon bonds, metal beta-diketonates, alkoxides, and dialkylamides are representative members of this class. Representative Organometallic Compounds Many complexes feature coordination bonds between a metal and organic ligands, the organic ligands often bind the metal through a heteroatom such as oxygen or nitrogen, in which case such compounds are considered coordination compounds. However, if any of the form a direct M-C bond, then complex is usually considered to be organometallic. Furthermore, many compounds such as metal acetylacetonates and metal alkoxides are called metalorganics. Many organic coordination compounds occur naturally, for example, hemoglobin and myoglobin contain an iron center coordinated to the nitrogen atoms of a porphyrin ring, magnesium is the center of a chlorin ring in chlorophyll. The field of inorganic compounds is known as bioinorganic chemistry. In contrast to these compounds, methylcobalamin, with a cobalt-methyl bond, is a true organometallic complex. This subset of complexes are often discussed within the subfield of bioorganometallic chemistry, the metal-carbon bond in organometallic compounds are generally highly covalent. For highly electropositive elements, such as lithium and sodium, the carbon ligand exhibits carbanionic character, but free carbon-based anions are extremely rare, as in other areas of chemistry, electron counting is useful for organizing organometallic chemistry. The 18-electron rule is helpful in predicting the stabilities of metal carbonyls, most organometallic compounds do not however follow the 18e rule. Chemical bonding and reactivity in organometallic compounds is often discussed from the perspective of the isolobal principle, as well as X-ray diffraction, NMR and infrared spectroscopy are common techniques used to determine structure. The dynamic properties of compounds is often probed with variable-temperature NMR. The abundant and diverse products from coal and petroleum led to Ziegler-Natta, Fischer-Tropsch, hydroformylation catalysis which employ CO, H2, recognition of organometallic chemistry as a distinct subfield culminated in the Nobel Prizes to Ernst Fischer and Geoffrey Wilkinson for work on metallocenes. In 2005, Yves Chauvin, Robert H. Grubbs and Richard R. Schrock shared the Nobel Prize for metal-catalyzed olefin metathesis,1900 Paul Sabatier works on hydrogenation organic compounds with metal catalysts
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Benzenehexol
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Benzenehexol, also called hexahydroxybenzene, is an organic compound with formula C6H6O6 or C66. It is a six-fold phenol of benzene, the product is also called hexaphenol, but this name has been used also for other substances. Benzenehexol is a crystalline solid soluble in hot water, with a point above 310°. It can be prepared from inositol, oxidation of benzenehexol yields tetrahydroxy-p-benzoquinone, rhodizonic acid, and dodecahydroxycyclohexane. Conversely, benzenehexol can be obtained by reduction of sodium THBQ salt with SnCl2/HCl, benzenehexol is a starting material for a class of discotic liquid crystals. Benzenehexol forms an adduct with 2, 2-bipyridine, with 1,2 molecular ratio, like most phenols, benzenehexol can lose the six H+ ions from the hydroxyl groups, yielding the hexaanion C6O66−. The potassium salt of this anion is one of the components of Liebigs so-called potassium carbonyl, the hexaanion is produced by trimerization of the acetylenediolate anion C 2O2−2 when heating potassium acetylenediolate K 2C 2O2. The nature of K 6C 6O6 was clarified by R. Nietzki and T. Benckiser in 1885, the lithium salt of this anion, Li6C6O6 has been considered for electric battery applications. Hexahydroxy benzene forms esters such as the hexaacetate C66 and ethers like hexa-tert-butoxybenzene C66
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Mesoxalic acid
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Mesoxalic acid, also called oxomalonic acid or ketomalonic acid, is an organic compound with formula C3H2O5 or HO-3-OH. Mesoxalic acid is both an acid and a ketonic acid. It readily loses two protons to yield the divalent anion C3O52−, called mesoxalate, oxomalonate, or ketomalonate. These terms are used for salts containing this anion, such as sodium mesoxalate, Na2C3O5. Mesoxalate is one of the anions, which consist solely of carbon. Mesoxalic acid readily absorbs and reacts with water to form a product commonly called mesoxalic acid hydrate, more properly dihydroxymalonic acid, in product catalogs and other contexts, the terms mesoxalic acid, oxomalonic acid, etc. often refer to this hydrated compound. In particular, the product traded as sodium mesoxalate monohydrate is almost always sodium dihydroxymalonate, the product can be obtained also by oxidation of tartronic acid or glycerol. Since they are carried out in water, these procedures generally give the dihydroxy derivative and it is also prepared by the oxidation of glycerol with the help of Bi3
35.
Carbon tetrachloride
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Carbon tetrachloride, also known by many other names is an organic compound with the chemical formula CCl4. It was formerly used in fire extinguishers, as a precursor to refrigerants. It is a liquid with a sweet smell that can be detected at low levels. It has practically no flammability at lower temperatures, in 1992, production in the U. S. /Europe/Japan was estimated at 720,000 tonnes. In the carbon tetrachloride molecule, four chlorine atoms are positioned symmetrically as corners in a tetrahedral configuration joined to a carbon atom by single covalent bonds. Because of this geometry, CCl4 is non-polar. Methane gas has the structure, making carbon tetrachloride a halomethane. As a solvent, it is suited to dissolving other non-polar compounds, fats. It is somewhat volatile, giving off vapors with a characteristic of other chlorinated solvents. Solid tetrachloromethane has two polymorphs, crystalline II below −47.5 °C and crystalline I above −47.5 °C. At −47.3 °C it has monoclinic crystal structure with space group C2/c, with a specific gravity greater than 1, carbon tetrachloride will be present as a dense nonaqueous phase liquid if sufficient quantities are spilled in the environment. In organic chemistry, carbon tetrachloride serves as a source of chlorine in the Appel reaction, prior to the Montreal Protocol, large quantities of carbon tetrachloride were used to produce the chlorofluorocarbon refrigerants R-11 and R-12. However, these play a role in ozone depletion and have been phased out. Carbon tetrachloride is used to manufacture less destructive refrigerants. Carbon tetrachloride has also used in the detection of neutrinos. It once was a popular solvent in chemistry, but, because of its adverse health effects. It is sometimes useful as a solvent for infrared spectroscopy, because there are no significant absorption bands >1600 cm−1, because carbon tetrachloride does not have any hydrogen atoms, it was historically used in proton NMR spectroscopy. In addition to being toxic, its power is low
36.
Mellitic acid
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Mellitic acid, also called graphitic acid or benzenehexacarboxylic acid, is an acid first discovered in 1799 by M. H. Klaproth in the mineral mellite, which is the aluminium salt of the acid. Mellitic acid may be prepared by warming mellite with ammonium carbonate, boiling off the excess of the ammonium salt, the precipitated alumina is filtered off, the filtrate evaporated, and the ammonium salt of the acid purified by recrystallization. The ammonium salt is converted into the lead salt by precipitation with lead acetate. The acid may also be prepared by the oxidation of carbon, graphite or hexamethyl benzene, by alkaline potassium permanganate in the cold. Mellitic acid crystallizes in fine silky needles and is soluble in water and it is a very stable compound, chlorine, concentrated nitric acid and hydriodic acid do not react with it. It is decomposed, on dry distillation, into carbon dioxide and pyromellitic acid, C10H6O8, long digestion of the acid with an excess of phosphorus pentachloride forms the acid chloride, which crystallizes in needles, and melts at 190 °C. By heating the salt of the acid to 150–160 °C while ammonia is evolved, a mixture of paramide. The mixture may be separated by dissolving out the ammonium euchroate with water, paramide is a white amorphous powder, insoluble in water and alcohol. Mellitates of iron and cobalt have interesting magnetic properties, mellitic anhydride Henry Enfield Roscoe, Carl Scholemmer, Mellitene Group, A Treatise on Chemistry, V. III, The Chemistry of the Hydrocarbons and their Derivatives on Organic Chemistry, P. V,529. This article incorporates text from a now in the public domain, Chisholm, Hugh
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Mars
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Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, after Mercury. Named after the Roman god of war, it is referred to as the Red Planet because the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the northern hemisphere covers 40% of the planet, Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Mars trojan, there are ongoing investigations assessing the past habitability potential of Mars, as well as the possibility of extant life. Future astrobiology missions are planned, including the Mars 2020 and ExoMars rovers, liquid water cannot exist on the surface of Mars due to low atmospheric pressure, which is about 6⁄1000 that of the Earths, except at the lowest elevations for short periods. The two polar ice caps appear to be largely of water. The volume of ice in the south polar ice cap, if melted. On November 22,2016, NASA reported finding a large amount of ice in the Utopia Planitia region of Mars. The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior, Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Its apparent magnitude reaches −2.91, which is surpassed only by Jupiter, Venus, the Moon, optical ground-based telescopes are typically limited to resolving features about 300 kilometers across when Earth and Mars are closest because of Earths atmosphere. Mars is approximately half the diameter of Earth with an area only slightly less than the total area of Earths dry land. Mars is less dense than Earth, having about 15% of Earths volume and 11% of Earths mass, the red-orange appearance of the Martian surface is caused by iron oxide, or rust. It can look like butterscotch, other common colors include golden, brown, tan. Like Earth, Mars has differentiated into a metallic core overlaid by less dense materials. Current models of its interior imply a core with a radius of about 1,794 ±65 kilometers, consisting primarily of iron and this iron sulfide core is thought to be twice as rich in lighter elements than Earths. The core is surrounded by a mantle that formed many of the tectonic and volcanic features on the planet
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Mellite
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Mellite, also called honeystone, is an unusual mineral being also an organic chemical. Chemically identified as a salt of mellitic acid, that is, aluminium benzene hexacarboxylate hydrate. It is a translucent honey-coloured crystal which can be polished and faceted to form striking gemstones and it crystallizes in the tetragonal system and occurs both in good crystals and as formless masses. It is soft with a Mohs hardness of 2 to 2.5 and has a low gravity of 1.6. It was discovered originally in 1789 at Artern in Thuringia in Germany it has also been found in Russia, Austria, the Czech Republic. It was named from the Greek μέλι meli honey, in allusion to its color and it is found associated with lignite and is assumed to be formed from plant material with aluminium derived from clay
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Tetrafluoromethane
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Tetrafluoromethane, also known as carbon tetrafluoride, is the simplest fluorocarbon. It has a high bond strength due to the nature of the carbon–fluorine bond. It can also be classified as a haloalkane or halomethane, Tetrafluoromethane is a potent greenhouse gas. Carbon–fluorine bonds are the strongest single bonds in organic chemistry, additionally, they strengthen as more carbon–fluorine bonds are added to the same carbon. This effect is due to the increased coulombic attractions between the atoms and the carbon because the carbon has a positive partial charge of 0.76. Tetrafluoromethane is the product when any carbon compound, including itself, is burned in an atmosphere of fluorine. With hydrocarbons, hydrogen fluoride is a coproduct and it was first reported in 1926. It can also be prepared by the fluorination of carbon dioxide, although it can be made from myriad precursors and fluorine, elemental fluorine is expensive and difficult to handle. SiC +4 F2 → CF4 + SiF4 Tetrafluoromethane, like other fluorocarbons, is stable due to the strength of its carbon–fluorine bonds. The bonds in tetrafluoromethane have an energy of 515 kJ⋅mol−1. As a result, it is inert to acids and hydroxides, however, it reacts explosively with alkali metals. Thermal decomposition or combustion of CF4 produces toxic gases and in the presence of water will also yield hydrogen fluoride and it is very slightly soluble in water, but miscible with organic solvents. Tetrafluoromethane is sometimes used as a low temperature refrigerant and it is used in electronics microfabrication alone or in combination with oxygen as a plasma etchant for silicon, silicon dioxide, and silicon nitride. It also has uses in neutron detectors Tetrafluoromethane is a potent greenhouse gas that contributes to the greenhouse effect, although structurally similar to chlorofluorocarbons, tetrafluoromethane does not deplete the ozone layer. This is because the depletion is caused by the atoms in CFCs. Carbon–fluorine bonds are stronger and less likely to dissociate, according to Guinness World Records Tetrafluoromethane is the most persistent greenhouse gas. Main industrial emissions of tetrafluoromethane besides hexafluoroethane are produced during production of aluminium using Hall-Héroult process, CF4 also is produced as product of the breakdown of more complex compounds such as halocarbons. Due to its density, tetrafluoromethane can displace air, creating a hazard in inadequately ventilated areas
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