Organic Chemistry

Organic chemistry is the chemistry of carbon compounds. All organic compounds contain carbon; however, there are some compounds of carbon that are not classified as organic. For example, salts such as carbonates (e.g., Na₂CO₃, CaCO₃) and cyanides (e.g., NaCN, KCN) are usually designated as inorganic. Perhaps a more useful description might be: Organic compounds are compounds of carbon that usually contain hydrogen and that may also contain other elements such as oxygen, nitrogen, sulfur, phosphorus, or halogen (F, Cl, Br, or I). In any case, there are very few carbon compounds that are not organic, while there are millions that are.

History

Prehistoric civilizations obtained many useful chemicals from plants and animals. They were familiar with sugar, which they learned to ferment to make wine. Then they found that the wine could turn into vinegar. Ancient Egyptians used blue dye made from the indigo in madder root, and a royal purple dye extracted from a rare kind of mollusk. Soap was made by heating animal fat with base from wood ashes.

During the Middle Ages dry distillation of wood yielded mixtures of methyl alcohol, acetone, and acetic acid. Alchemists isolated cholesterol from gallstones, morphine from opium, and drugs such as quinine, strychnine, and brucine from various plants. Two hundred years ago chemists such as Antoine Lavoisier determined the elemental composition of many of these substances and noted that they all contained carbon and hydrogen, and that many also contained oxygen and nitrogen. It also appeared that there were two classes of materials: the mineral type (generally hard, high-melting, and noncombustible), and the organic type (often soft, liquid or low melting solids, and frequently easily combustible materials). Most organic chemicals could be burned to produce carbon dioxide; and any hydrogen present was converted to water (H₂O). Because organic compounds had for centuries been isolated only from plants and animals, it was commonly believed that some "vital force" in living things was necessary to produce them. This belief persisted until 1828, when Friedrich Wöhler was able to make urea, a chemical found in the urine of animals, from the inorganic salt ammonium cyanate.

Since that time organic chemistry has grown into a vast and ever expanding field that encompasses millions of chemical compounds.

Scope of Organic Chemistry

The field of organic chemistry includes more than twenty million compounds for which properties have been determined and recorded in the literature. Many hundreds of new compounds are added every day. Much more than half of the world's chemists are organic chemists. Some new organic compounds are simply isolated from plants or animals; some are made by modifying naturally occurring chemicals; but most new organic compounds are actually synthesized in the laboratory from other (usually smaller) organic molecules. Over the years organic chemists have developed a broad array of reactions that allow them to make all kinds of complex products from simpler starting materials.

Singular Attributes of Carbon

When one considers the millions of chemical compounds that are known and notes that more than 95 percent of them are compounds of carbon, one realizes that carbon is unique. Why are there so many carbon compounds? It turns out that atoms of carbon are quite remarkable in a number of ways.

Carbon atoms form very strong bonds with other carbon atoms. The bonds are so strong that carbon can form long chains, some containing thousands of carbon atoms. (Carbon is the only element that can do this.)

A carbon atom forms four bonds, therefore carbon not only can form long chains, but it also forms chains that have branches. It is a major reason why carbon compounds exhibit so much isomerism. The simple compound decane (C₁₀H₂₂), for example, has 75 different isomers .

Carbon atoms can be bonded by double or triple bonds as well as single bonds. This multiple bonding is much more prevalent with carbon than with any other element.

Carbon atoms can form rings of various sizes. The rings may be saturated or unsaturated. The unsaturated 6-membered ring known as the benzene ring is the basis for an entire subfield of "aromatic" organic chemistry.

Carbon atoms form strong bonds not only with other carbon atoms but also with atoms of other elements. In addition to hydrogen, many carbon compounds also contain oxygen. Nitrogen, sulfur, phosphorus, and the halogens also frequently occur in carbon compounds.

Various kinds of functional groups occur widely among carbon compounds, and many different kinds of isomers are possible.

Hydrocarbons

Compounds of carbon and hydrogen only are called hydrocarbons. These are the simplest compounds of organic chemistry. The most basic group of hydrocarbons are the alkanes, which contain only single bonds. The simplest member of the alkane series is methane, CH₄, the main component of natural gas. The names of some alkanes are listed in Table 1. Alkanes sometimes

ALKANES
Formula		Name
CH4	CH4	methane	gases
C2H6	CH3CH3	ethane
C3H8	CH3CH2CH3	propane
C4H10	CH3CH2CH2CH3	butane
C5H12	CH3(CH2)3CH3	pentane	liquids
C6H14	CH3(CH2)4CH3	hexane
C7H16	CH3(CH2)5CH3	heptane
C8H18	CH3(CH2)6CH3	octane
C9H20	CH3(CH2)7CH3	nonane
C10H22	CH3(CH2)8CH3	decane
C11H24	CH3(CH2)9CH3	undecane
C12H26	CH3(CH2)10CH3	dodecane
C13H28	CH3(CH2)11CH3	tridecane
C14H30	CH3(CH2)12CH3	tetradecane
C15H32	CH3(CH2)13CH3	pentadecane
C16H34	CH3(CH2)14CH3	hexadecane
C17H36	CH3(CH2)15CH3	heptadecane
C18H38	CH3(CH2)16CH3	octadecane	solids
C19H40	CH3(CH2)17CH3	nonadecane
C20H42	CH3(CH2)18CH3	eicosane

have ring structures. Since a 4-carbon chain of the alkane series is called butane, a ring of 4 carbon atoms is called cyclobutane.

Simple hydrocarbons that contain one or more double bonds are called alkenes. They are named like alkanes, but their names end in " –ene." The simplest alkene has two carbon atoms and is called ethene. A 3-carbon chain that has a double bond is called propene.

A 5-carbon hydrocarbon chain with a double bond is called pentene, and if the double bond links the second and third carbons, it is 2-pentene. Like cycloalkanes, alkenes have the general formula C_nH_2n. Alkenes having ring structures are called cycloalkenes. A 5-carbon ring with a double bond is called cyclopentene.

Hydrocarbons that contain one or more triple bonds are called alkynes, and is the name ending is "–yne." A 2-carbon alkyne is therefore named ethyne. (However, the compound is often referred to by its common name, which is acetylene. )

Compounds that contain double or triple bonds are said to be "unsaturated"—because they are not "saturated" with hydrogen atoms. Unsaturated compounds are reactive materials that readily add hydrogen when heated over a catalyst such as nickel. The reverse reaction also occurs. Heating ethane with steam is an important commercial process for making ethene (or ethylene). This is an important commercial process called "steam cracking."

When a 6-carbon ring contains 2 double bonds, it is called cyclohexadiene, but when it has 3 double bonds, it is not called cyclohexatriene; this is because a 6-carbon ring with three double bonds takes on a special kind of stability. The double bonds become completely conjugated and no longer behave as double bonds. The ring, known as a "benzene ring," is said to be aromatic.

The removal of a hydrogen atom from a hydrocarbon molecule leaves an alkyl group that readily attaches to a functional group, or forms a branch on a hydrocarbon chain. The groups are named after the corresponding hydrocarbons. For example, CH₃– is named methyl; CH₃CH₂–, ethyl; CH₂= CH–, ethenyl; CH₃CH₂CH₂–, propyl; and so on. A benzene ring from which a hydrogen atom has been removed is often referred to as a phenyl. The branched molecules shown here would be given names as follows

Theoretically there is no limit to the length of hydrocarbon chains. Very large hydrocarbon molecules (polymers) have been made containing as many as 100,000 carbon atoms. However, such molecules are hard to make and very difficult to melt and to shape into useful products.

Hydrocarbons are obtained primarily from fossil fuels—especially petroleum and natural gas. Natural gas is a mixture that is largely methane mixed with varying amounts of ethane and other light hydrocarbons, while petroleum is a complex mixture of many different hydrocarbons. Coal, the other fossil fuel, is a much more complicated material from which many kinds of organic compounds, some of them hydrocarbons, can be obtained.

Functional Groups

Alkane molecules are rather unreactive (except for being very flammable), but alkenes react with many other substances. When a drop of bromine is added to an alkene, for example, the deep orange color of the bromine immediately disappears as the bromine adds across the double bond to form a dibromo derivative. The double bond is called a "functional group" because its presence in a molecule causes reactivity at that particular site. There are a dozen or so functional groups that appear frequently in organic compounds. Some of the most common ones are listed in Table 2. The same molecule may contain several functional groups. Aspirin, for example, is both a carboxylic acid and an ester , and cholesterol is an alkene as well as an alcohol.

Isomerism

Isomers are molecules with the same molecular formula but different structures. There is only one structure for methane, ethane, or propane; but butane, C₄H₁₀, can have either of two different structure:

The linear molecule (1) is called butane, or normal butane (n -butane), whereas the branched molecule (2) is methylpropane (rather than 2-methylpropane, as the methyl group has to be in a 2-position). If the methyl group of (2) were attached to a terminal carbon, the resultant molecule would be the same as (1). Methylpropane (2) is also called iso butane.

In a conjugated system, there are alternating double and single bonds, allowing electrons to flow back and forth. Molecules that contain such conjugated systems are said to be stabilized by "resonance." In the benzene ring every other bond is a double bond, all the way around the ring. This results in a special kind of stabilization called "aromaticity," in which the electrons are delocalized and free to travel all around the ring. Certain ring compounds, like benzene, that contain such a conjugated system of double and single bonds are described as "aromatic."

Pentane has 3 isomers: pentane (or n -pentane), methylbutane (or iso- pentane), and dimethyl propane (or neo pentane). Hexane has 5 isomers: hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, and 2,3-dimethylbutane. Heptane has 9 different isomers, octane has 18, nonane has 35, and decane has 75. An increase in the number of carbon atoms greatly increases the possibilities for isomerism. There are more than 4,000 isomers of C₁₅H₃₂ and more than 366,000 isomers of C₂₀H₄₂. The formula C₃₀H₆₂ has more than 4 billion. Of course, most of them have never been isolated as pure compounds (but could be, if there were any point in doing it).

For molecules other than hydrocarbons, still other kinds of isomers are possible. The simple formula C₂H₆O can represent ethyl alcohol or dimethyl ether; and C₃H₆O could stand for an alcohol, an ether, an aldehyde , or a ketone (among other things). The larger a molecule is, and the greater the variety of atoms and functional groups it contains, the more numerous its isomers.

There is still another kind of isomerism that stems from the existence of "right-" and "left-handed" molecules. It is sometimes referred to as optical isomerism because the molecules that make up a pair of these isomers usually differ only in the way they rotate plane polarized light.

Nomenclature

There are so many millions of organic compounds that simply finding names for them all is a major challenge. It was not until the late nineteenth century that chemists developed a logical system for naming organic compounds. Compounds had often been named according to their sources. The 1-carbon carboxylic acid, for example, was first obtained from ants, and so it was called formic acid, from the Latin word for ants (formicae ). The 2-carbon acid was obtained from vinegar (acetum in Latin), and was called acetic acid.

To bring some order to the naming process an international meeting was held in 1892 at Geneva, Switzerland. The group later became known as the International Union of Pure and Applied Chemistry (IUPAC). Its objective was to establish a naming process that would provide each compound with a unique and systematic name. An initial set of rules was adopted at that first meeting in Geneva, and IUPAC has continued that work. Its systematic naming rules are used by organic chemists all over the world. The names of the alkanes form the basis for the system, with functional groups usually being indicated with appropriate suffixes. Some examples are given in Table 2.

Organic Reactions

Organic chemistry is concerned with the many compounds of carbon, their names, their isomers, and their properties, but it is mostly concerned with their reactions. Organic chemists have developed a huge array of chemical reactions that can convert one organic compound to another. Some reactions involve addition of one molecule to another; some involve decomposition of molecules; some involve substitution of one atom or group by another; and some even involve the rearrangement of molecules, with some atoms moving into new positions. Some reactions require energy in the form of heat or radiation; and some require a special kind of catalyst or some sort

NAMING ORGANIC COMPOUNDS
Functional Group		Type Compound	Example	IUPAC Name	Common Name
C=C	double bond	alkene	H2C=CH2	ethene	ethylene
C≡C	triple bond	alkyne	HC≡CH	ethyne	acetylene
–OH	hydroxyl	alcohol	CH3OH	methanol	methyl alcohol
–O–	oxy	ether	H3COCH3	methoxymethane	methyl ether
	carbonyl	aldehyde	H2C=0	methanal	formaldehyde
	carbonyl	ketone	CH3COCH3	propanone	acetone
	carboxyl	carboxylic acid	HCOOH	methanoic acid	formic acid
	carboxyl	ester	HCOOCH2CH3	ethyl methanoate	ethyl formate
–NH2	amino	amine	CH3NH2	aminomethane	methylamine
–CN	cyano	nitrile	CH3CN	ethanenitrile	acetonitrile
–X	halogen	haloalkane	CH3Cl	chloromethane	methyl chloride

of solvent. Of course, not all organic reactions are highly successful. One reaction might be a very simple one giving essentially 100 percent of the desired product; but another might be a complex multistep process yielding less than 5 percent overall of the wanted product.

Organic reactions can often give remarkable control as to what products should be formed. Adding water to propene for example, produces 2-propanol in the presence of acid, but it yields 1-propanol if treated first with B₂H₆ and then H₂O₂ in the presence of base.

Future Sources of Organic Chemicals

Fossil fuels have been our primary natural source for many organic chemicals for more than a century, but our fossil fuel resources are finite, and they are being rapidly depleted (especially oil and gas). What will be our sources of organic materials in the future? Since fossil fuels are nonrenewable resources, it is believed that the twenty-first century will see a shift toward greater dependence on renewable raw materials. The largest U.S. chemical company has a goal of becoming 25 percent based on renewable resources by 2010. It is already producing 1,3-propanediol from cornstarch using a gene-tailored E. coli bacterium. This diol is used in Du Pont's fiber Sorona, which is said to combine the best features of both polyester and nylon fibers. Succinic acid and polyhydroxybutyrate are also obtainable from renewable crops, and the list of such renewable raw materials is destined to grow. For example, ethylene (or ethene), CH₂=CH₂, which is a highly important commercial chemical used in making many industrial chemicals and polymers, is presently made by steam cracking of ethane obtained from oil or natural gas; but ethylene can also be made by dehydration of ethyl alcohol made by fermentation of sugar. Efforts are even being made to use biowaste materials, such as corn husks, nutshells, and wood chips as industrial raw materials.

Analytical Tools

Organic chemists often need to examine products for identification, purity analysis, or structure determination. There are some marvelous tools available to help them do these things. Chromatography , spectroscopy , and crystallography are especially widely used in organic chemistry.

Column chromatography, gas chromatography, and liquid chromatography are all important methods for separating mixtures of organic compounds. Spectroscopic tools include ultraviolet (UV), infrared (IR), nuclear magnetic resonance (NMR), and mass spectroscopy (MS), each capable of providing a different kind of information about an organic compound. Although it is limited to substances that can be prepared as pure crystals, x-ray crystallography is probably the ultimate tool for determining molecular structure.

Careers in Organic Chemistry

Some organic chemists are involved in basic research at government or academic institutions, but most have careers in industry. The industries vary from oil and chemical companies to industries producing food, pharmaceuticals, cosmetics, detergents, paints, plastics, pesticides, textiles, or other kinds of products. Many organic chemists work in laboratories, where they do various kinds of analysis or research, but many others do not. Some are teachers, or writers, or science librarians. Some study law and become patent attorneys; some study medicine and become medical researchers; and some study business and become administrators of companies, colleges, or other institutions. Organic chemistry is an enormous field full of many kinds of career possibilities.

see also Fossil Fuels; Lavoisier, Antoine; Organic Halogen Compounds; WÖhler, Friedrich.

Kenneth E. Kolb

Bibliography

Atkins, Robert C., and Carey, Francis A. (2002). Organic Chemistry: A Brief Course, 3rd edition. Boston: McGraw-Hill.

Bailey, Philip S., Jr., and Bailey, Christina A. (2000). Organic Chemistry: A Brief Survey of Concepts and Applications, 6th edition. Upper Saddle River, NJ: Prentice Hall.

Brown, William H., and Foote, Christopher S. (2002). Organic Chemistry, 3rd edition. San Diego: Saunders.

Fessenden, Ralph J.; Fessenden, Joan S.; and Logue, Marshall (1998). Organic Chemistry, 6th edition. Pacific Grove, CA: Brooks/Cole.

Solomons, T. W. Graham (1997). Fundamentals of Organic Chemistry, 5th edition. New York: Wiley.

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Curie

Curie , family of French scientists. Pierre Curie, 1859-1906, scientist, and his wife, Marie Sklodowska Curie, 1867-1934, chemist and physicist, b. Warsaw, are known for their work on radioactivity and on radium. The Curies' daughter Irène (see under Joliot-Curie , family) was also a scientist.

Pierre Curie's early work dealt with crystallography and with the effects of temperature on magnetism; he discovered (1883) and, with his brother Jacques Curie, investigated piezoelectricity (a form of electric polarity) in crystals. Marie Sklodowska's interest in science was stimulated by her father, a professor of physics in Warsaw. In 1891 she went to Paris to continue her studies at the Sorbonne. In 1895 she married Pierre Curie and engaged in independent research in his laboratory at the municipal school of physics and chemistry where Pierre was director of laboratories (from 1882) and professor (from 1895).

Following A. H. Becquerel 's discovery of radioactivity, Mme Curie began to investigate uranium, a radioactive element found in pitchblende. In 1898 she reported a probable new element in pitchblende, and Pierre Curie joined in her research. They discovered (1898) both polonium and radium, laboriously isolated one gram of radium salts from about eight tons of pitchblende, and determined the atomic weights and properties of radium and polonium. The Curies refused to patent their processes or otherwise to profit from the commercial exploitation of radium. For their work on radioactivity they shared with Becquerel the 1903 Nobel Prize in Physics.

The Sorbonne created (1904) a special chair of physics for Pierre Curie; Marie Curie was appointed his successor after his death in a street accident. She also retained her professorship (assumed in 1900) at the normal school at Sèvres and continued her research. In 1910 she isolated (with André Debierne) metallic radium. As the recipient of the 1911 Nobel Prize in Chemistry she was the first person to be awarded a second Nobel Prize. She was made director of the laboratory of radioactivity at the Curie Institute of Radium, established jointly by the Univ. of Paris and the Pasteur Institute, for research on radioactivity and for radium therapy.

During World War I, Mme Curie devoted her energies to providing radiological services for hospitals. In 1921 a gram of radium, a gift from American women, was presented to her by President Harding; this she accepted in behalf of the Curie Institute. A second gram, presented in 1929, was given by Mme Curie to the newly founded Curie Institute in Warsaw. Five years later she died from the effects of radioactivity. In 1995 Marie and Pierre Curie's ashes were enshrined in the Panthéon, Paris; she was the first woman to be honored so in her own right.

Bibliography: Among the numerous and valuable writings of the Curies are Marie Curie's doctoral dissertation, Radioactive Substances (1902, 2 vol.; tr. 1961); Traité de radioactivité (1910); Radioactivité (1935); and her biography of Pierre Curie (1923, tr. 1923). Pierre Curie's collected works appeared in 1908. A biography of Marie Curie was written by a daughter, Ève Curie (tr. 1937). See also biographies by R. W. Reid (1974), F. Giroud (tr. 1986), S. Quinn (1995), and B. Goldsmith (2004).
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adapted from: "Curie." The Columbia Encyclopedia, Sixth Edition. 2008. Encyclopedia.com. 12 Mar. 2009 <http://www.encyclopedia.com>.

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Contributions of Ancient Arabian and Egyptian Scientists on Chemistry

Contributions of Ancient Arabian and Egyptian Scientists on Chemistry
Md. Wasim Aktar* and M. Paramasivam
Deptt. of Agril. Chemicals, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal, India.

Abstracts
The modern chemistry is based on the findings and thinking of the people of historical age. If no one knows the base and work of the previous on a subject, he or she could mere develop a new thought or findings. For, a civilization must know its past. Hence, the present work is a small effort to find out the contribution of ancient Arabian and Egyptian scientists in the field of Chemistry. Different scientists of different school of thought, correlating different streams of science being Chemistry as a main subject, are described in the present work.
Chemistry deals with the composition and properties of substances and the changes of composition they undergo. It has been divided into Inorganic and Organic. The conception of this in modern Chemistry came from al-Rãzi’s classification of chemical substances into mineral, vegetable and animal. Inorganic Chemistry, deals with the preparation and properties of the elements, and their compounds, originally arose from the study of minerals and metals, whereas Organic Chemistry, which deals with carbon compounds, developed through the investigation of animal and plant products.
Prior to 1828 it was not possible to synthesize organic substances from their elements and, therefore, it was supposed that there existed fundamental difference between Organic and Inorganic Chemistry. In 1828 F. Wohler synthetically prepared urea, an organic substance; thereby revealing that there was no fundamental difference between these two branches of Chemistry. Since carbon compounds were numerous, their study separately made under Organic Chemistry, and study of elements and non-carbon compounds included in Inorganic Chemistry’. (1)
The earliest discoveries in Inorganic Chemistry were made in metallurgy, Materia Medica, painting, enameling, glazing, glass-making, arts, etc. These arts, and many metals, compounds and alloys were known to the Arabs. Similarly, the discoveries in Organic Chemistry were made in the arts of dyeing, tanning, the manufacture of paper, in the study of fats, both of plant and animal origin, in medicine, etc. Thus Chemistry had its sources in photo techniques, mineralogy, metallurgy, Materia Medica and decorative arts. It is the product of transmutation of baser metals into gold
and philosophical thoughts of practical or theoretical interest. Finally, it is the result of the study of the properties of the substances.
A Greek philosopher, Empedocles, held the view that all the four elements, air, water, earth and fire, were the primal elements, and that the various substances were made by their intermixing. He regarded them to be distinct and unchangeable. Aristotle considered these elements to be changeable i.e., one kind of matter could be changed into another kind. (2)
Jábir ibn Hayyãn (Liatinized as Geber), a great Arabian Chemist of the 8th century A.C., modified the Aristotelian doctrine of the four elements, and presented the so-called sulphur-mercury theory of metals. According to this theory metals differ essentially because of different proportions of sulphur and mercury in them. He also formulated the theory of geologic formation of metals.
Unlike his Greek predecessors, he did not merely speculate, but performed experiments to reach certain conclusions. He recognized and stated the importance of experimentation in Chemistry. He combined the theoretical knowledge of the Greeks and practical knowledge of the craftsmen, and himself made noteworthy advance both in the theory and practice of Chemistry.
Jâbir’s contribution to Chemistry is very great. He gave a scientific description of two principle operations of Chemistry. One of them is calcinations which is employed in the extraction of metals from their ores. The other is reduction which is employed in numerous chemical treatments. He improved upon the methods of evaporation, melting, distillation, sublimation and crystallization. These are the fundamental methods employed for the purification of chemical substances, enabling the chemist to study their properties and uses, and to prepare them. The process of distillation is particularly applied for taking extract of plant material.
In the opinion of Jàbir the cultivation of gold was not the only object of a chemist. The preparation of new chemical substances was also regarded by him as the chief object of Chemistry. We owe to him for the first preparation of such substances as arsenic and antimony from their sulphides, and basic lead carbonate. He also did important work in the preparation of steel, and the refinement of metals. Jàbir also deals with such applications as the use of manganese dioxide in glass-making, varnishes to water-proof cloth and protect iron use of iron pyrites for writing in gold and distillation of vinegar to concentrate acetic acid.
The most important discovery made by Jabir was the preparation of sulphuric acid. The importance of this discovery can be realized by the fact that in this modern age the extent of the industrial progress of a country is mostly judged by the amount of. sulphuric acid consumed in that country. Another important acid prepared by him was nitric acid which he obtained by distilling a mixture of alum (of Yemen) and copper sulphate (of Cyprus). Then by dissolving ammonium chloride into this acid, he prepared aqua regia which, unlike acids, could dissolve gold in it.
Jabir classified chemical substances, on the basis of some distinctive features, into bodies (gold, silver, etc.) and souls (mercury, sulphur, etc.) to make the study of their properties easier.
Jãbir is the author of a large number of books on chemistry and a book on astrolabe. About one hundred chemical works ascribed to him are extant. His fame chiefly rests on his chemical books preserved in Arabic. (3)
We find that the author recognized and stated clearly the importance of experimentation more clearly than any other early chemist. He remarkably sound views on methods of chemical research. It is impossible to reach definite conclusions regarding the extent of his contributions until all the Arabic writings ascribed to him have been properly edited and studied. But on the basis of our present knowledge, Jabir appears to be one of the greatest scientist whose influence can be traced throughout the whole period of the historical development of the Arabian and European chemistry. In the light of these facts it would not be improper to call Jãbir as the father of Chemistry.
Some of the chemical writings to which Jãbir’s name is attached were translated into Latin. The first such version, the Book of the Composition of Alchemy was made by Robert of Chester in 1144. The Kitab al-Sab’in (the book of the seventy) was translated by Gerard of Cremona in the 12th century’. The translation of the Sum of Perfection was made by Richard Russell. One of his books has been translated into French by Berthelot. (4)
Several technical terms have passed from Jãbir’s Arabic writings through Latin into the European languages. Among these are realgar (red sulphide of arsenic), tutia (zinc oxide), alkali, antimony, and alembic for distillation Vessel. The Arabic equivalents for the last three words are alqali, ithmad, and al-’anbiq respectively. (5)
Before Jãbir Ibn Hayyan, the Umayyad prince Khalid Ibn Yazid, who was a philosopher, poet and chemist, encouraged Greek philosophers in Egypt to translate Greek scientific works into Arabic. These were among the earliest translations in Arabic from other languages. He was himself deeply interested in medicine, astrology and chemistry. Many chemical works are ascribed to him. One of them is entitled Firdaus al-Hikmah fi’Ilm al-Kimiya. This work was in verse, and contained 2,315 couplets. (6)
An encyclopaedic scientist, and philosopher, Abu Yusuf Ya’qub al-Kindi considered the art of transformation of one metal into the other as an imposture. A few of ‘his numerous works dealing with many sciences are extant. One of his works is on pharmacy, a branch of applied chemistry. (7)

Chemistry was usually mixed up with mineralogy and geology. The oldest Arabian lapidary which may serve as an important source of chemistry was written by ‘Utärid Ibn Muhammad al-Hãsib who flourished in the ninth century. It deals with the properties of precious stones. (8)
In the same century Jãbir’s work was further advanced by al-Räzi who wrote many chemical treatises, and described a number of chemical instruments. One of his treatises consists of 25 pieces of chemical apparatus. He made investigations on specific gravity. One of his important works is on the art of transformation of baser metals into the noble ones. He applied his chemical knowledge for medical purposes, thus laying the foundation of Iatrochemistry. (9)
Other important chemists of this century were Dhu’l-Nün and al-Jàhiz. The former mostly dealt with the art of transmutation of metals. (10) The latter prepared ammonia from animal offals by dry distillation. (11)
In the tenth century Ibn Wahshiyah wrote on chemistry, His work may help to understand chemical symbolism. Maslamah Ibn Ahmad, an astronomer, mathematician and oculist of this century wrote two chemical works entitled, Rutbat al-Hakim and Ghãyat al-Hakim. The second is well known in the Latin translation made in 1252 by the order of King Alfonso under the title Picatrix. (12)
A Persian pharmacologist Abü Mansür Muwaffaq Ibn ‘Ali al-Harawi who flourished in Herat in the tenth century, was apparently the first to think of compiling a treatise on Materia Medica in Persian. He travelled extensively in Persia and India to obtain necessary information. He wrote, between 968 and 977, a book entitled Kitab al-Abniyah ‘an Haqã’iq al-Adwiyah. It contains Greek, Syrian, Arabian, Persian, and Indian knowledge. It deals with 585 remedies (of which 466 are derived from plants, 75 from minerals, and 44 from animals). He classified them into four groups according to their action, and gave the outline of a general pharmacological theory.
Abu Mansür distinguished between sodium carbonate (natrum) and potassium carbonate (qali). He had some knowledge of arsenious oxide, cupric oxide, silicic acid, antimony and so on. He knew the toxicological effects of copper and lead compounds, the depilatory virtue of quicklime, the composition of plaster of Paris and its surgical use. (13)
The greatest Arabian surgeon, Khalaf Ibn ‘Abbäs al-Zahrãwi (d. 1013) wrote a great medical encyclopaedia, al-Tasrif in 30 sections, which contains interesting methods of preparing drugs by sublimation and distillation, but its most important part is the surgical one. (14)
Abü Rayhan Muhammad al-Birüni (973—1048) took a great interest in the determination of the specific gravity of eighteen precious stones and metals. A voluminous unedited lapidary by al- Biruni is extant in unique manuscript in the Escorial Library. It contains a description of a great number of stones and metals from the natural, commercial, and medical point of view. Moreover, he composed a pharmacology (saydalah).Important information could certainly be obtained from his unedited works, on the origin of Indian and Chinese stones and drugs, which appeared in early Arabic scientific works. (15)
Ibn Sinà wrote a treatise on minerals, which was very important and one of the main sources of geological knowledge, also a source of chemistry in Western Europe until the Renaissance.
As mentioned before, mineralogy stood in close relation to chemistry. Nearly fifty Arabic lapidaries have been named. The best known of them is. the ‘Flowers of Knowledge of Stones’, by Shihàb al-Din al-Tifãshi (died in Cairo in 1154). It gives in 25 chapters extensive information on the subject of the same number of precious stones, their origin, geography, examination, purity, price, application for medicinal and magical purposes, and so on. Except for Pliny and the superior Aristotelian lapidary, he quotes only Arabic authors. (16)

The output of the books on Chemistry was very great after the eleventh century. Thus, there are known books of about forty Arabic and Persian chemists. Ibn Khaldun, (d. 1406) the talented Arabian philosopher of history and the greatest intellect of his century, was a violent opponent of the idea of transmutation of metals by chemical means. (17)
Some chemists thought that one metal can be transformed into another by artificial methods. For such transformation they followed different procedures depending on the character and form of the chemical treatment and the substance chosen for this purpose; the substance being called the ‘Noble Stone’ or ‘Philosopher’s Stone’. This may be excrements, or blood, or hair, or eggs, or anything else. After the substance has been specified, it is treated along certain lines mentioned in their books. The result is an earthen or fluid substance which is called Elixir. These chemists think that if Elixir is added to silver which has been heated in a fire, the silver turns into gold. If added to copper which had been heated in a fire, the copper turns into silver.
The question arises whether the metals are of specific differences, each constituting a distinct species, or whether they differ in certain properties and qualities and constitute different kinds of one and the same species?
Abü Nasr al-Färabi and his followers held the opinion that the difference in metals is caused by certain conditions such as humidity and dryness, softness and hardness, and colours such as yellow, white and black. According to him the metals are different kinds of one and the same species.
On the other hand, Ibn Sina and his followers believed that metals have specific differences and belong to different species, each of which has its own differential and genus, like all other species.
According to Abü Nasr al-Färãbi, it is possible to transform one metal into another, because it is possible to change their conditions.
“Ibn Sinà thought that such transformation was impossible. His assumption is based on the fact that specific differences in metals cannot be changed by artificial means. He believed that since the metals are created by the Creator and Determiner of things, God Almighty, and the mystery of their real character was utterly unknown and could not be perceived, any attempt for transformation would be meaningless”. (18)
Ancient Arabs’ art of transformation of metals was based upon Hellenistic and Iranian traditions, but apparently the main principles and the main operations were already established long before the 12th century. Before this century the Arabs had not only made many experiments, and produced several works on this art, but they had begun to doubt and criticise the most advanced theories concerning it. This proves that the standard of their chemical thinking was advanced.
The 12th and 13th centuries added very little to their knowledge about the transformation of metals, but their research continued in various fields. The main chemical writer of this age was Abu‘l-Qãsim Muhammad al-Iraqi who flourished in the second half of the 13th century. He was an experimenter and a theorist. His works represent the full development of the Arabic doctrine. (19)
The 14th century was an enlightened period when a group of intelligent writers began to reject the idea of transformation of metals by chemical means. One of such person was a historian, Rashid al-Din who described such chemical practice in Mongol Persia and expressed his distrust of such chemists. The large encyclopaedic work Nukhbat al-Dahr of al-Dimashqi contains, in part second, much information on metal, their properties, and influences. (19) As usual in Arabic treatises, chemistry is mixed up with mineralogy and geology. (20)
Even in their purely chemical researches on transformation of metals, the Arab chemists achieved by no means unimportant results. In their efforts to discover Elixir they often discovered new chemical processes, and hit upon the catalytic properties of various substances. The pains, which they took in the search of gold, ultimately resulted in their great contribution to the development of modern chemistry.
The last important chemist of the 14th century was ‘Izz al-Din ‘Ali Ibn al- Jildaki. Some twenty treatises are ascribed to him. The list shows al-Jildaki’s great activity as a chemical writer. A complete study of his vast writings is necessary to know what he actually tried to establish. To some extent, this study was made by Ruska, Stapleton, Holm yard, and their disciples.
One of al-Jildaki’s important books entitled Nihâyat al-Talab fi Sharh al-Muktasab contains many quotations from the earlier works, and some novelties, as the use of nitric acid to extract silver out of the gold-silver alloy. Al- Jildaki remarked that the substances do not react except by definite weights. (21) This is one of the four fundamental laws of modern chemistry.
The ancient chemists applied their chemical knowledge to a large number of industrial arts. Only three such arts are mentioned here, which will enable the readers to estimate the extent of their knowledge of Applied Chemistry.
Paper:
Paper was invented by the Chinese who prepared it from the cocoon of the silkworm. Some specimens of Chinese paper extant date back to the second century A.C. The first manufacture of the paper outside China occurred in Samarqand (757). When Samarqand was captured by Arabs the manufacture of paper spread over the whole Arab world including the Maghrib. (Tunis, Morocco, Algiers).

By the end of the 12th century there were four hundred paper mills in Fasalone. In Spain the main centre of manufacture of paper was Shatiba which remained a ancient Arab city until 1239. Cordova was the centre of the business of paper in Spain.
The Arabs developed this art. They prepared paper not only from silk, but also from cotton, rags and wood.In the middle of the 10th century the paper industry was introduced in Spain. In Khurasan paper was made of linen.
There is an early treatise dealing with paper-making, the Umdat al-Kuttab wa ‘Uddatu dhawi’l-Albãb which is ascribed to the Amir al- Mu’izz’ Ibn Badis, a ruler of the Zayri dynasty (1015—61) in Tunis. The 11th chapter of this treatise, dealing with paper, has been edited, translated and elaborately discussed by the foremost student of Arabic paper, Josef Karabacek. This work explains how to prepare the pulp, make the sheets, wash and clean them, colour, polish and paste them, and give them an antique appearance. No text comparable to this in any other language of so early a date is known.
The preparation of pulp involves a large number of complicated chemical processes, which shows the advancement of the chemical knowledge of the Arabs and Egyptians at that time.
The manufacture of writing-paper in Spain is one of the most beneficial contributions of Arabs to Europe. Without paper the scale on which popular education in Europe developed would have not been possible. The preparation of paper from silk would have been impossible in Europe due to the lack of silk production there. The Arabs method of producing paper from cotton could only be useful for the Europeans. After Spain the art of paper-making was established in Italy (1268—76). France owed its first paper mills to ancient Spain. From these countries the industry spread throughout Europe.
Another type of paper; marbled paper, which was common upon end-papers, paper covers and edges of books, was prepared in the East, and exported to the West. About the preparation of marbled paper Roger Bacon tells us: “The Turks have a pretty art of chamoletting of paper, which is not with us in use. They take diverse oiled colours, and put them severally (in drops) upon water; and stirr the water lightly and then wet their paper (being of some thickness) with it, and the paper will be waved, and veined, like Chamolet or Marble’.
Books bound in the West towards the end of the 16th century are found with end-papers brought from the East, but it was not until about a century later that European binders began to make them themselves. Hand-made marbled papers are now rarely used, but more or less clumsily reproduced imitations still serve various purposes.

There is an Arabic word ‘rizma’ meaning a bundle of merchandise, which had been adopted in almost every Western language with slight variations to mean a bundle of paper (English: ream). This also testifies to the Arabic origin of that business in the West. (22)
Tiles :
The industry of tile-making which involves a large number of complex technical and chemical processes, was highly developed by Arabs. The earliest treatise, a Persian text, dealing with the manufacture of faience, was unique of its kind in world literature until the 16th century. It has been written by ‘Abd Allah Ibn ‘Ali Kàshàni in the 13th century. This book entitled Jawahir al-‘Arã’is Wa Aja’ib al-Nafä’is was written on precious stones and perfumes. It explains the manufacture of Faience, the ingredients (as clay, borax, feldspar, cobalt, lapis lazuli, lead, manganese, tin etc.), their mixtures, the kiln processes and implements, the methods of glazing and decorating. This treatise is similar to the various other treatises on precious stones written in Arabic and Persian. The final chapter deals with the art of enamelled pottery. This account is specially valuable because it is based on actual and traditional practice. The maker of the beautiful lustre ‘mihrab’ (arch) of the tomb of Imam Yahyã (now in the Hermitage, Leningrad), dated 1305 A.C., Yusuf Ibn ‘Ali Ibn Muhammad, was possibly a brother of the author. (23)
Ceramics:
The early history of Arabian and Egyptian ceramics has not so far been written. Many interesting specimens have been discovered in recent years which throw much light on the development of this industry in the Arab world. The centers of this industry were situated in Persia, Mesopotamia, Syria, Egypt and Valencia from where various types spread rapidly throughout the Islamic Caliphate.
Under Arabian influence the potters in these Centers revived old technical processes, developed new ones and began to experiment with decorative and ornamental schemes. The Arabian potters readily absorbed progressive ideas but at
the same time maintained great originality. Two types of pottery were in common use; enamelled and lustered. In enamelled pottery (the glazed earthenware) the Ancient s, from an early period, were expert masters. In lustered pottery also they made great progress. “In this the design is painted in a metallic salt on a glazed surface and fixed by firing in smike in a way that gives it a metallic gleam, which varies in different specimens from a bright copper-red to a greenish- yellow tint, and in some cases throws off brilliant iridescent reflections. (24)
In the last chapter of the Persian text Kitab al-Jawähir’ al-’Ara’is Wa ‘Ajã’ib al-Nafa’is, the author describes the techniques of glazing
with two fires (lustres), leaf building, over glaze decoration fired in a muffle kiln. (i.e.,
separated from the flame, the source of heat being outside), haf’t rang, a Persian term
referring to the seven colours of the planets. There may be a reference to the polychrome over glaze technique, the so called minai ware (another Persian term; mina-wash means lustre; mina coloured). The author indicates differences between the art as practiced in Kashan, Baghdad and Tabriz. In Baghdad and Tabriz other kinds of firewood and potash were used.
In the 15th century the Arabian ceramic art was followed by Italian potters, who obtained much of the mature technical knowledge from Arab sources. This technical knowledge proved to be helpful in the revival of ceramic art during the Renaissance. (25)
REFERENCES :-
1. Encyclopaedia Britannica, chicago, 1951, p.360
2. Ibid., p. 355.
3 Sarton George, Introduction to the History of Science, Washington, 1950, Vol I. p. 532.
4. Wasiti, Hakim Nayyar, Tibb al-’Arab ( ãn Urdu Translation of Arabian Medicine by Edward G. Browne), Lahore, 1954, p. 26.
5. Ibid.
6. Hãji Khalifah, Kashf al-Zunün, Istanbul, 1943. Vol., I, p. 1254.
Al-Zirakli, Khair al-Din, Al-’Alãm vol. II p. 342.
7. Sarton, op. cit., p. 559.
8. Ibid., p. 572. Al-Qifti, op. cit. p. 251.
9. Ibid., p. 271. Sarton, op. cit. p. 609.
10. lbid, p. 592.
11. lbid, p. 597.
12. Ibid., pp. 620, 668.
13. Ibid., p. 678.
14. Ibid., p. 681.
15 Ibid., p. 707.
16. Ibid, vol. II, part II, p. 650.

17. Ibn Khaldun, Muqaddimah, English translation by Frenz Rosenthal, London, 1957, vol. 3, p. 267.
18. Ibid. p. 278
19. Haji. Khalifah, op. cit. p. 1936.
20. Sarton, op. cit vol. III, part I, p. 759.
21. Ibid. Vol. II, Part. II, p. 1045.
22. Sarton, op. cit., Vol. III, Part I, p. 321.
23. Sarton, op. cit vol. III , part I, p. 756.
24 Arnold and Guillaume, op. cit. p. 125.

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About the Author:
The author is now engaged in various aspects of research work mainly in the field of Analytical Chemistry with special reference to Agricultural Science. He is currently working as a Senior Research Fellow in Export Testing Laboratory under Deptt of Agril. Chemicals in BCKV. He has completed his B.Sc. (Ag.) Hons from Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal, India in 2004. He has got his M.Sc.(Ag. Chemicals) degree from the same university in 2006. He was awarded with Karunamoyee Gold Medal from the same university for his out standing academic performance as well as significant achievements regarding his research work during his P.G. curriculam. He has attended a no. of national and international seminars, symposiums, workshops. He has a no. of papers in various journal of national and international repute.

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Chemistry and Goals of Chemists

Chemistry is a science of substances, their properties, and how and why materials combine or separate to form different substances. Atoms, molecules and compounds are the involved ones in the study of Chemistry. In other words, it is how atoms interact to form molecules and how molecules interact with each other. It also looks into the composition of substances and their properties. The outer electron orbits or shells primarily determine the chemical characteristics of a material and whether materials will chemically combine. Thus Chemistry is the study of the composition of matter and the changes that take place in that composition. If we place a bar of iron outside our window, the iron bar will soon begin to rust. If we pour vinegar on baking soda, the mixture fizzes. If we hold a sugar cube over a flame, the sugar begins to turn brown and give off steam. The goal of chemistry is to understand the composition of substances such as iron, vinegar, baking soda, and sugar and to understand what happens during the changes described here.

The term chemistry has grown out of an earlier field of study known as alchemy. Alchemy has been described as a kind of pre-chemistry, in which scholars studied the nature of matter but without the formal scientific approach that modern chemists use. The term alchemy is probably based on the Arabic name for Egypt, al-Kimia, or the "black country." Ancient scholars learned a great deal about matter, usually by trial- and-error methods. For example, the Egyptians mastered many technical procedures such as making different types of metals, manufacturing colored glass, dying cloth, and extracting oils from plants. Alchemists of the Middle Ages discovered a number of elements and compounds and perfected other chemical techniques, such as distillation and crystallization. The modern subject of chemistry did not appear, however, until the eighteenth century. At that point, scholars began to recognize that research on the nature of matter had to be conducted according to certain specific rules. Among these rules was one stating that ideas in chemistry had to be subjected to experimental tests. Nowadays keeping in view the overall significance and versatility of chemistry, we can say that:

Chemistry is a science: There is only one sanctioned procedure for determining whether a statement about matter is really chemistry: the exhaustive, inefficient, but highly successful scientific method. Chemists often arrive at new results by nonscientific means (like luck or sheer creativity), but their work isn't chemistry unless it can be reproduced and verified scientifically.

Chemistry is a systematic study: Chemists have devised several good methods for solving problems and making observations. For example, analytical chemists often use protocols (thoroughly tested recipes) for determining the concentrations of substances in a sample. Chemists use well-defined techniques like spectroscopy and chromatography to study new or unknown substances.

Chemistry is the study of the composition and properties of matter: Chemistry is the study of the composition and properties of matter as it answers questions like, "What kind of stuff is a sample made of? What does the sample look like on a molecular scale? How does the structure of the material determine its properties? How do the properties of the material change when we increase temperature, or pressure, or some other environmental variable?"

Chemistry is the study of the reactivity of substances: Chemistry is the study of the reactivity of substances as one material can be changed into another by a chemical reaction. A complex substance can by made from simpler ones. Chemical compounds can break down into simpler substances. For example, fuels burn, food cooks, leaves turn their colors in the fall, cells grow, medicines cure and it is both their chemistry and the chemistry which is concerned with the essential processes that make these changes happen. Today, the science of chemistry is often divided into four major areas: organic, inorganic, physical, and analytical chemistry. Each discipline investigates a different aspect of the properties and reactions of matter.

Organic chemistry: Organic chemistry is the study of carbon compounds. That definition sometimes puzzles beginning chemistry students because more than 100 chemical elements are known. How does it happen that one large field of chemistry is devoted to the study of only one of those elements and its compounds? The answer to that question is that carbon is a most unusual element. It is the only element whose atoms are able to combine with each other in apparently endless combinations. Many organic compounds consist of dozens, hundreds, or even thousands of carbon atoms joined to each other in a continuous chain. Other organic compounds consist of carbon chains with other carbon chains branching off them. Still other organic compounds consist of carbon atoms arranged in rings, cages, spheres, or other geometric forms. The scope of organic chemistry can be appreciated by knowing that more than 90 percent of all compounds known to science (more than 10 million compounds) are organic compounds. Organic chemistry is of special interest because it deals with many of the compounds that we encounter in our everyday lives: natural and synthetic rubber, vitamins, carbohydrates, proteins, fats and oils, cloth, plastics, paper, and most of the compounds that make up all living organisms, from simple one-cell bacteria to the most complex plants and animals.

Inorganic chemistry: Inorganic chemistry is the study of the chemistry of all the elements in the periodic table except for carbon. Like their cousins in the field of organic chemistry, inorganic chemists have provided the world with countless numbers of useful products, including fertilizers, alloys, ceramics, household cleaning products, building materials, water softening and purification systems, paints and stains, computer chips and other electronic components, and beauty products. The more than 100 elements included in the field of inorganic chemistry have a staggering variety of properties. Some are gases, others are solid, and a few are liquid. Some are so reactive that they have to be stored in special containers, while others are so inert (inactive) that they virtually never react with other elements. Some are so common they can be produced for only a few cents a pound, while others are so rare that they cost hundreds of dollars an ounce. Because of this wide variety of elements and properties, most inorganic chemists concentrate on a single element or family of elements or on certain types of reactions.

Physical chemistry: Physical chemistry is the branch of chemistry that investigates the physical properties of materials and relates these properties to the structure of the substance. Physical chemists study both organic and inorganic compounds and measure such variables as the temperature needed to liquefy a solid, the energy of the light absorbed by a substance, and the heat required to accomplish a chemical transformation. A computer is used to calculate the properties of a material and compare these assumptions to laboratory measurements. Physical chemistry is responsible for the theories and understanding of the physical phenomena utilized in organic and inorganic chemistry.

Analytical chemistry: Analytical chemistry is that field of chemistry concerned with the identification of materials and with the determination of the percentage composition of compounds and mixtures. These two lines of research are known, respectively, as qualitative analysis and quantitative analysis. Two of the oldest techniques used in analytical chemistry are gravimetric and volumetric analysis. Gravimetric analysis refers to the process by which a substance is precipitated (changed to a solid) out of solution and then dried and weighed. Volumetric analysis involves the reaction between two liquids in order to determine the composition of one or both of the liquids.

In the last half of the twentieth century, a number of mechanical systems have been developed for use in analytical research. For example, spectroscopy is the process by which an unknown sample is excited (or energized) by heating or by some other process. The radiation given off by the hot sample can then be analyzed to determine what elements are present. Various forms of spectroscopy are available (X-ray, infrared, and ultraviolet, for example) depending on the form of radiation analyzed. Other analytical techniques now in use include optical and electron microscopy, nuclear magnetic resonance (MRI; used to produce a three-dimensional image), mass spectrometry (used to identify and find out the mass of particles contained in a mixture), and various forms of chromatography (used to identify the components of mixtures).

Other fields of chemistry: The division of chemistry into four major fields is in some ways misleading and inaccurate. In the first place, each of these four fields is so large that no chemist is an authority in any one field. An inorganic chemist might specialize in the chemistry of sulfur, the chemistry of nitrogen, the chemistry of the inert gases, or in even more specialized topics. Secondly, many fields have developed within one of the four major areas, and many other fields cross two or more of the major areas. For an example of specialization, the subject of biochemistry is considered a subspecialty of organic chemistry. It is concerned with organic compounds that occur within living systems. An example of a cross-discipline subject is bioinorganic chemistry. Bioinorganic chemistry is the science dealing with the role of inorganic elements and their compounds (such as iron, copper, and sulfur) in living organisms. At present, chemists explore the boundaries of chemistry and its connections with other sciences, such as biology, environmental science, geology, mathematics, and physics. A chemist today may even have a so-called nontraditional occupation. He or she may be a pharmaceutical salesperson, a technical writer, a science librarian, an investment broker, or a patent lawyer, since discoveries by a traditional chemist may expand and diversify into a variety of fields that encompass our whole society.

Chemists have two major goals. One is to find out the composition of matter in order to learn what elements are present in a given sample and in what percentage and arrangement. This type of research is known as analysis. A second goal is to invent new substances that replicate or are different from those found in nature. This form of research is known as synthesis. In many cases, analysis leads to synthesis. That is, chemists may find that some naturally occurring substance is a good painkiller. That discovery may suggest new avenues of research that will lead to a synthetic (human-made) product similar to the natural product, but with other desirable properties (and usually lower cost). Many of the substances that chemistry has produced for human use have been developed by this process of analysis and synthesis.

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About the Author:

Dr.Badruddin Khan teaches Chemistry in the University of kashmir, srinagar, India. His E.mail is:khanbudr@yahoo.co.in

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What is Chemistry and How to Tame It?

Chemistry is the study of matter and its changes. This includes everything in the universe from a simple hydrogen atom to very large replicating molecules in life processes. Chemistry is involved with the development of medicines that control and cure diseases; food production through specific and safe agricultural chemicals; consumer products such as cleaners, plastics and clothing; new methods of energy production, transfer and storage; new materials for electronic components; and new methods for protection and cleanup of the environment. Chemists are needed to help solve some of society's most difficult technological problems through research, development and teaching.

A major branch of chemistry, known as ‘Inorganic Chemistry’, is generally considered to embrace all substances except hydrocarbons and their derivatives, or all substances that are not compounds of carbon (including some of the small molecules of carbon.) It covers a broad range of subjects, among which are atomic structure, crystallography, chemical bonding, coordination compounds, acid-base reactions, ceramics, and various subdivisions of electrochemistry (electrolysis, battery science, corrosion, semi conduction, etc.). It is important to state that inorganic and organic chemistry often overlap. For example, chemical bonding applies to both disciplines, electrochemistry and acid-base reactions have their organic counterparts, catalysts and coordination compounds may be either organic or inorganic.

Regarding the importance of inorganic chemistry, R.T. Sanderson has written: "All chemistry is the science of atoms, involving an understanding of why they possess certain characteristic qualities and why these qualities dictate the behavior of atoms when they come together. All properties of material substances are the inevitable result of the kind of atoms and the manner in which they are attached and assembled. All chemical change involves a rearrangement of atoms. Inorganic chemistry (is) the only discipline within the chemistry that examines specifically the differences among all the different kinds of atoms".

Another major branch of chemistry is ‘Organic Chemistry’ which embraces all compounds of carbon except such binary compounds as the carbon oxides, the carbides, carbon disulfide, etc.; such ternary compounds as the metallic cyanides, metallic carbonyls, phosgene (COCl2), carbonyl sulfide (COS), etc.; and the metallic carbonates, such as calcium carbonate and sodium carbonate. The total number of organic compounds is indeterminate, but a huge number has been identified and named. Important areas of organic chemistry include polymerization, hydrogenation, Isomerisation, fermentation, photochemistry, and stereochemistry. There is no sharp dividing line between organic and inorganic chemistry, for the two often tend to overlap.

Application of the concepts and laws of physics to chemical phenomena is included under the heading ‘Physical Chemistry’ in order to describe in quantitative (mathematical) terms a vast amount of qualitative (observational) information. A selection of only the most important concepts of physical chemistry would include: the electron wave equation and the quantum mechanical interpretation of atomic and molecular structure, the study of the subatomic fundamental particles of matter, application of thermodynamics to heats of formation of compounds and the heats of chemical reaction, the theory of rate processes and chemical equilibria, orbital theory and chemical bonding, surface chemistry, including catalysis and finely divided particles, the principles of electrochemistry and ionization. Although physical chemistry is closely related to both inorganic and organic chemistry, it is considered a separate discipline.

Analytical Chemistry is the subdivision of chemistry concerned with identification of materials (qualitative analysis) and with determination of the percentage composition of mixtures or the constituents of a pure compound (quantitative analysis). The gravimetric and volumetric (or "wet") methods (precipitation, titration and solvent extraction) are still used for routine work and new titration methods have been introduced e.g. cryoscopic, pressure-metric (for reactions that produce a gaseous product), redox methods, and use of a F-sensitive electrode etc. However, faster and more accurate techniques (collectively called instrumental) have been developed in the recent past. Among these are infrared, ultraviolet, and x-ray spectroscopy where the presence and amount of a metallic element is indicated by lines in it's emission or absorption spectrum; colorimetry by which the percentage of a substance in soluble is determined by the intensity of it's colour; chromatography of various types by which the components of a liquid or gaseous mixture are determined by passing it through a column of porous material or on thin layers of finely divided solids; and separation of mixtures in ion exchange columns and radioactive tracer analysis. Optical and electron microscopy, mass spectrometry, microanalysis, Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) spectroscopy all fall within the area of analytical chemistry. New and highly sophisticated techniques have been introduced in recent years, in many cases replacing traditional methods.

Originally Biochemistry was a subdivision of chemistry but now an independent science, which includes all aspects of chemistry that apply to living organisms. Thus, photochemistry is directly involved with photosynthesis and physical chemistry with osmosis, two phenomena that underline all plant and animal life. Other important chemical mechanisms that apply directly to living organisms are catalysis, which takes place in biochemical systems by the agency of enzymes; nucleic acid and protein constitution and behavior, which is known to control the mechanism of genetics; colloid chemistry, which deals in part with the nature of cell walls, muscles, collagen, etc; acid-base relations, involved in the pH of body fluids; and such nutritional components as amino acids, fats, carbohydrates, minerals, lipids and vitamins, all of which are essential to life. The chemical organization and reproductive behavior of microorganisms (bacteria and viruses) and a large part of agricultural chemistry are also included in biochemistry. Particularly active areas of biochemistry are nucleic acids, cell surfaces (membranes), enzymology, peptide hormones, molecular biology, and recombinant DNA.

Nuclear Chemistry is the division of chemistry dealing with changes in or transformations of the atomic nucleus. It includes spontaneous and induced radioactivity, the fission or splitting of nuclei, and their fusion, or union; also the properties and behavior of the reaction products and their separation and analysis. The reactions involving nuclei are usually accompanied by large energy changes, far greater than those of chemical reactions; that are carried out in nuclear reactors for electric power production and manufacture of radioactive isotopes for medical use, also (in research work) in cyclotrons.

Stoichiometry is the branch of chemistry and chemical engineering that deals with the quantities of substances that enter into, and are produced by, chemical reactions. Stoichiometry provides the quantitative relationship between reactants and products in a chemical reaction. For example, when methane unites with oxygen in complete combustion, 16g of methane require 64g of oxygen. At the same time 44g of carbon dioxide and 36g of water are formed as reaction productions. Every chemical reaction has its characteristic proportions. The method of obtaining these from chemical formulas, equations, atomic weights and molecular weights, and determination of what and how much is used and produced in chemical processes, is the major concern of Stoichiometry.

Many students treat chemistry as "too difficult to understand and prefer to escape and memorize even on the expense of the realization that by doing so they are bound to harm themselves now and deprive the society of their contribution later. Henceforth they should note that although it is somewhat challenging, any reasonably intelligent and dedicated student can succeed in chemistry. They should also realize that there is no use of wasting both money and time for some thing that is either memorized before examination or forgotten thereafter or some portion of it is dropped under the pretext of selection of important topics for the purpose of preparation for examination. One must not waste his/her valuables (money and time) just for the sake of degree and literacy as both of these are bound to have detrimental consequences not only for the individual concerned but also the society for obvious reasons.

Those of the students who get their confidence shattered whenever they come across chemistry may note Some Tips (given below) from tose who have succeeded in Chemistry

1. Develop good study habits.
2. Attend all lectures and labs.
3. Take all lecture notes and make your own notes after understanding things properly.
4. Use your lecture notes as a guide to your reading in the textbook. Write your questions down if you don't understand something. Ask your teacher if you don't understand a concept.
5. Make flash cards of definitions, concepts, reactions, structures, and nomenclature that are in the textbook and are emphasized by your teacher in lecture.
6. Remember that writing something is equivalent to reading it ten times and notes are records for recollecting the material and not something to be memorized in a capsule form.
7. Do all the homework problems sincerely and with sincerity.
8. One of the best ways of learning is to find a study partner or to form a study group and work on problems independently and then together.
9. Keep yourself up –to- date. If you get behind or get a poor grade in class tests, either you want to drop the class or may be made to drop the class.
10. Try to see the ‘big picture; of the future instead of being mean and escapist.
11. Practice applying what you have learned in class to the world around you.
12. Try to foster your own scientific curiosity and wonder around ‘why things are and how they happen’.
13. Have a positive attitude.
14. Realize that science requires more self discipline, but offers more rewards.
15. Try to be organized and recognized.
16. Persevere and be determined to succeed.

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Dr.Badruddin Khan teaches Chemistry in the University of Kashmir, Srinagar, India.

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Atom

atom [Gr.,=uncuttable (indivisible)], basic unit of matter ; more properly, the smallest unit of a chemical element having the properties of that element.

Structure of the Atom

The atom consists of a central, positively charged core, the nucleus , and negatively charged particles called electrons that are found in orbits around the nucleus.

The Nucleus

Almost the entire mass of the atom is concentrated in the nucleus, which occupies only a tiny fraction of the atom's volume. The nucleus of an atom consists of neutrons and protons, the neutron being an uncharged particle and the proton a positively charged one. Their masses are almost equal. Atoms containing the same number of protons but different numbers of neutrons represent different forms, or isotopes , of the same element.

The Electrons

Surrounding the nucleus of an atom are its electrons; for a neutral atom, the number of electrons is equal to the atomic number. The outermost electrons of an atom determine its chemical and electrical properties. An atom may combine chemically with another atom in various ways, either by giving up or receiving electrons, thus setting up an electrical attraction between the atoms (see ion ), or by sharing one or more pairs of electrons (see chemical bond ). Because metals have few outermost electrons and tend to give them up easily, they are good conductors of electricity or heat (see conduction ).

The electrons are often described as revolving about the nucleus as the planets revolve about the sun. This picture, however, is misleading. The quantum theory has shown that all particles in motion also have certain wave properties. For a particle the size of an electron, these properties are of considerable importance. As a result the electrons in an atom cannot be pictured as localized in space, but rather should be viewed as smeared out over the entire orbit so that they form a cloud of charge. The electron clouds around the nucleus represent regions in which the electrons are most likely to be found. The shapes of these clouds can be very complex, in marked contrast to the simple elliptical orbits of planets. Surprisingly, the sizes of all atoms are comparable, in spite of the large differences in the number of electrons they contain.

Atomic Weight and Number

The atomic number of an atom is simply the number of protons in its nucleus. The atomic weight of an atom is given in most cases by the mass number of the atom, equal to the total number of protons and neutrons combined. An atom may be conveniently symbolized by its chemical symbol with the atomic number and mass number written as subscript and superscript, respectively. For example, the symbol for uranium is U (atomic number 92); the isotopes of uranium with atomic weights 235 and 238 are indicated by ²³⁵₉₂ U and ²³⁸₉₂ U.

Development of Atomic Theory

Early Atomic Theory

The atomic theory, which holds that matter is composed of tiny, indivisible particles in constant motion, was proposed in the 5th cent. BC by the Greek philosophers Leucippus and Democritus and was adopted by the Roman Lucretius. However, Aristotle did not accept the theory, and it was ignored for many centuries. Interest in the atomic theory was revived during the 18th cent. following work on the nature and behavior of gases (see gas laws ).

From Dalton to the Periodic Table

Modern atomic theory begins with the work of John Dalton, published in 1808. He held that all the atoms of an element are of exactly the same size and weight (see atomic weight ) and are in these two respects unlike the atoms of any other element. He stated that atoms of the elements unite chemically in simple numerical ratios to form compounds. The best evidence for his theory was the experimentally verified law of simple multiple proportions , which gives a relation between the weights of two elements that combine to form different compounds.

Evidence for Dalton's theory also came from Michael Faraday's law of electrolysis . A major development was the periodic table , devised simultaneously by Dmitri Mendeleev and J. L. Meyer, which arranged atoms of different elements in order of increasing atomic weight so that elements with similar chemical properties fell into groups. By the end of the 19th cent. it was generally accepted that matter is composed of atoms that combine to form molecules.

Discovery of the Atom's Structure

In 1911, Ernest Rutherford developed the first coherent explanation of the structure of an atom. Using alpha particles emitted by radioactive atoms, he showed that the atom consists of a central, positively charged core, the nucleus , and negatively charged particles called electrons that orbit the nucleus. There was one serious obstacle to acceptance of the nuclear atom, however. According to classical theory, as the electrons orbit about the nucleus, they are continuously being accelerated (see acceleration ), and all accelerated charges radiate electromagnetic energy. Thus, they should lose their energy and spiral into the nucleus.

This difficulty was solved by Niels Bohr (1913), who applied the quantum theory developed by Max Planck and Albert Einstein to the problem of atomic structure. Bohr proposed that electrons could circle a nucleus without radiating energy only in orbits for which their orbital angular momentum was an integral multiple of Planck's constant h divided by 2π. The discrete spectral lines (see spectrum ) emitted by each element were produced by electrons dropping from allowed orbits of higher energy to those of lower energy, the frequency of the photon of light emitted being proportional to the energy difference between the orbits.

Around the same time, experiments on x-ray spectra (see X ray ) by H. G. J. Moseley showed that each nucleus was characterized by an atomic number, equal to the number of unit positive charges associated with it. By rearranging the periodic table according to atomic number rather than atomic weight, a more systematic arrangement was obtained. The development of quantum mechanics during the 1920s resulted in a satisfactory explanation for all phenomena related to the role of electrons in atoms and all aspects of their associated spectra. With the discovery of the neutron in 1932 the modern picture of the atom was complete.

Contemporary Studies of the Atom

With many of the problems of individual atomic structure and behavior now solved, attention has turned to both smaller and larger scales. On a smaller scale the atomic nucleus is being studied in order to determine the details of its structure and to develop sources of energy from nuclear fission and fusion (see nuclear energy ), for the atom is not at all indivisible, as the ancient philosophers thought, but can undergo a number of possible changes. On a larger scale new discoveries about the behavior of large groups of atoms have been made (see solid-state physics ). The question of the basic nature of matter has been carried beyond the atom and now centers on the nature of and relations between the hundreds of elementary particles that have been discovered in addition to the proton, neutron, and electron. Some of these particles have been used to make new types of exotic "atoms" such as positronium (see antiparticle ) and muonium (see muon ).

Bibliography

See G. Gamow, The Atom and Its Nucleus (1961); H. A. Boorse and L. Motz, ed., The World of the Atom (2 vol., 1966); B. H. Bransden and C. J. Joachain, Physics of Atoms and Molecules (1986).

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adapted from: "atom." The Columbia Encyclopedia, Sixth Edition. 2008. Encyclopedia.com. 10 Mar. 2009 <http://www.encyclopedia.com>.

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Atom

The atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in the case of Hydrogen-1, which is the only stable isotope with no neutron). The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain bound to each other, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral, otherwise it has a positive or negative charge and is an ion. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determine the isotope of the element.

The name atom comes from the Greek ἄτομος/átomos, α-τεμνω, which means uncuttable, something that cannot be divided further. The concept of an atom as an indivisible component of matter was first proposed by early Indian and Greek philosophers. In the 17th and 18th centuries, chemists provided a physical basis for this idea by showing that certain substances could not be further broken down by chemical methods. During the late 19th and early 20th centuries, physicists discovered subatomic components and structure inside the atom, thereby demonstrating that the 'atom' was not indivisible. The principles of quantum mechanics were used to successfully model the atom.^[1][2]

Relative to everyday experience, atoms are minuscule objects with proportionately tiny masses. Atoms can only be observed individually using special instruments such as the scanning tunneling microscope. Over 99.9% of an atom's mass is concentrated in the nucleus,^{[note 1]} with protons and neutrons having roughly equal mass. Each element has at least one isotope with unstable nuclei that can undergo radioactive decay. This can result in a transmutation that changes the number of protons or neutrons in a nucleus. Electrons that are bound to atoms possess a set of stable energy levels, or orbitals, and can undergo transitions between them by absorbing or emitting photons that match the energy differences between the levels. The electrons determine the chemical properties of an element, and strongly influence an atom's magnetic properties.

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adapted from: http://en.wikipedia.org/wiki/Atom

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