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Dictionary: chem·is·try (kĕm'ĭ-strē) pronunciation

n., pl., -tries.

The science of the composition, structure, properties, and reactions of matter, especially of atomic and molecular systems.
The composition, structure, properties, and reactions of a substance.
The elements of a complex entity and their dynamic interrelation: "Now that they had a leader, a restless chemistry possessed the group" (John Updike).
Mutual attraction or sympathy; rapport: The chemistry was good between the partners.

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5min Related Video: Chemistry

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US History Encyclopedia: Chemistry

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Chemistry is the study of the chemical and physical change of matter.

Early U.S. Chemistry and Chemical Societies

The beginning of chemistry in the United States came in the form of manufacturing goods such as glass, ink, and gunpowder. In the mid-1700s, some academic instruction in chemistry started in Philadelphia. The earliest known academic institution to formally teach chemistry was the medical school of the College of Philadelphia, where Benjamin Rush was appointed the chair of chemistry in 1769. Not only was Rush the first American chemistry teacher, he may have been the first to publish a chemistry textbook written in the United States. In 1813, the Chemical Society of Philadelphia published the first American chemical journal, Transactions. Although other chemical societies existed at that time, the Philadelphia Chemical Society was the first society to publish its own journal. Unfortunately, the journal and chemical society lasted only one year.

Sixty years later, in 1874, at Joseph Priestley's home in Northumberland, Pennsylvania, a number of renowned scientists gathered to celebrate Priestley's 1774 discovery of oxygen. It was at this gathering that Charles F. Chandler proposed the concept of an American chemical society. The proposal was turned down, in part because the American Association for the Advancement of Science (AAAS) had a chemical section that provided an adequate forum for assembly and debate. Two years later, a national society, based in New York and called the American Chemical Society, was formed with John W. Draper as its first president. Since New York chemists dominated most of the meetings and council representative positions, the Washington Chemical Society was founded in 1884 by two chemists based in Washington, D.C., Frank W. Clarke and Harvey W. Wiley. In 1890, the American Chemical Society constitution was changed to encourage the formation of local sections, such as New York, Washington, and other chemical societies in the United States, thereby leading to a national organization. By 1908, the society had approximately 3,400 members, outnumbering the German Chemical Society, which at that time was the center of world chemistry. Today, the American Chemical Society has some 163,503 members, and the United States is considered the center of world chemistry. In addition to its premier journal, the Journal of the American Chemical Society, the society also publishes several other journals that are divisional in nature, including the Journal of Organic Chemistry, Analytical Chemistry, Journal of Physical Chemistry, Inorganic Chemistry, and Biochemistry. The society also produces a publication called Chemical Abstracts, which catalogs abstracts from thousands of papers printed in chemical journals around the world.

European Influences

Although the various disciplines of chemistry—organic, inorganic, analytical, biochemistry, and physical chemistry—have a rich American history, they have also been influenced by European, especially German, chemists. The influence of physical chemistry on the development of chemistry in the United States began with American students who studied under a number of German chemists, most notably the 1909 Nobel Prize winner, Wilhelm Ostwald. In a 1946 survey by Stephen S. Visher, three of Ostwald's students were recognized as influential chemistry teachers—Gilbert N. Lewis, Arthur A. Noyes, and Theodore W. Richards. Of these three, Richards would be awarded the 1914 Nobel Prize for his contributions in accurately determining the atomic weight of a large number of chemical elements. Lewis and Noyes would go on to play a major role in the development of academic programs at institutions such as the University of California at Berkeley, the Massachusetts Institute of Technology, and Caltech. While at these institutions Lewis and Noyes attracted and trained numerous individuals, including William C. Bray, Richard C. Tolman, Joel H. Hildebrand, Merle Randall, Glenn T. Seaborg, and Linus Pauling. These individuals placed physical chemistry at the center of their academic programs and curricula. Students from these institutions, as well as other universities across America, took the knowledge they gained in physical chemistry to places like the Geophysical Laboratories, General Electric, Pittsburgh Plate Glass Company, and Bausch and Lomb.

Influence could also flow from America to Europe, as it did with one of the earliest great American chemists, J. Willard Gibbs (1839–1903). Gibbs, educated at Yale University, was the first doctor of engineering in the United States. His contribution to chemistry was in the field of thermodynamics—the study of heat and its transformations. Using thermodynamic principles, he deduced the Gibbs phase rule, which relates the number of components and phases of mixtures to the degrees of freedom in a closed system. Gibbs's work did not receive much attention in the United States due to its publication in a minor journal, but in Europe his ideas were well received by the physics community, including Wilhelm Ostwald, who translated Gibbs's work into German.

A second influence from Europe came around the 1920s, when a very bright student from Caltech named Linus Pauling went overseas as a postdoctoral fellow for eighteen months. In Europe, Pauling spent time working with Niels Bohr, Erwin Schrödinger, Arnold Sommerfeld, Walter Heitler, and Fritz London. During this time, Pauling trained himself in the new area of quantum mechanics and its application to chemical bonding. A significant part of our knowledge about the chemical bond and its properties is due to Pauling. Upon his return from Europe, Pauling went to back to Caltech and in 1950 published a paper explaining the nature of helical structures in proteins.

At the University of California at Berkeley, Gilbert N. Lewis directed a brilliant scientist, Glenn T. Seaborg. Seaborg worked as Lewis's assistant on acid-base chemistry during the day and at night he explored the mysteries of the atom. Seaborg is known for leading the first group to discover plutonium. This discovery would lead him to head a section on the top secret Manhattan Project, which created the first atomic bomb. Seaborg's second biggest achievement was his proposal to modify the periodic table to include the actinide series. This concept predicted that the fourteen actinides, including the first eleven transuranium elements, would form a transition series analogous to the rare-earth series of lanthanide elements and therefore show how the transuranium elements fit into the periodic table. Seaborg's work on the transuranium elements led to his sharing the 1951 Nobel Prize in chemistry with Edwin McMillan. In 1961, Seaborg became the chairman of the Atomic Energy Commission, where he remained for ten years.

Perhaps Seaborg's greatest contribution to chemistry in the United States was his advocacy of science and mathematics education. The cornerstone of his legacy on education is the Lawrence Hall of Science on the Berkeley campus, a public science center and institution for curriculum development and research in science and mathematics education. Seaborg also served as principal investigator of the well-known Great Explorations in Math and Science (GEMS) program, which publishes the many classes, workshops, teacher's guides, and handbooks from the Lawrence Hall of Science. To honor a brilliant career by such an outstanding individual, element 106 was named Seaborgium.

Twentieth-Century Research and Discoveries

Research in the American chemical industry started in the early twentieth century with the establishment of research laboratories such as General Electric, Eastman Kodak, AT&T, and DuPont. The research was necessary in order to replace badly needed products and chemicals that were normally obtained from Germany. Industry attracted re-search chemists from their academic labs and teaching assignments to head small, dynamic research groups. In 1909, Irving Langmuir was persuaded to leave his position as a chemistry teacher at Stevens Institute of Technology to do research at General Electric. It was not until World War I that industrial chemical research took off. Langmuir was awarded a Nobel Prize for his industrial work. In the early 1900s, chemists were working on polymer projects and free radical reactions in order to synthesize artificial rubber. DuPont hired Wallace H. Carothers, who worked on synthesizing polymers. A product of Carothers's efforts was the synthesis of nylon, which would become DuPont's greatest moneymaker. In 1951, modern organometallic chemistry began at Duquesne University in Pittsburgh with the publication of an article in the journal Nature on the synthesis of an organo-iron compound called dicyclopentadienyliron, better known as ferrocene. Professor Peter Pauson and Thomas J. Kealy, a student, were the first to publish its synthesis, and two papers would be published in 1952 with the correct predicted structure. One paper was by Robert Burns Woodward, Geoffrey Wilkinson, Myron Rosenblum, and Mark Whiting; the second was by Ernst Otto Fischer and Wolfgang Pfab. Finally, a complete crystal structure of ferrocene was published in separate papers by Phillip F. Eiland and Ray Pepinsky and by Jack D. Dunitz and Leslie E. Orgel. The X-ray crystallographic structures would confirm the earlier predicted structures. Ferrocene is a "sandwich" compound in which an iron ion is sandwiched between two cyclopentadienyl rings. The discovery of ferrocene was important in many aspects of chemistry, such as revisions in bonding concepts, synthesis of similar compounds, and uses of these compounds as new materials. Most importantly, the discovery of ferrocene has merged two distinct fields of chemistry, organic and inorganic, and led to important advances in the fields of homogeneous catalysis and polymerization.

Significant American achievements in chemistry were recognized by the Nobel Prize committee in the last part of the twentieth century and the first years of the twenty-first century. Some examples include: the 1993 award to Kary B. Mullis for his work on the polymerase chain reaction (PCR); the 1996 award to Robert F. Curl Jr. and Richard E. Smalley for their part in the discovery of C60, a form of molecular carbon; the 1998 award to John A. Pople and Walter Kohn for the development of computational methods in quantum chemistry; the 1999 award to Ahmed H. Zewail for his work on reactions using femtosecond (10^-14 seconds) chemistry; the 2000 award to Alan G. MacDiarmid and Alan J. Heeger for the discovery and development of conductive polymers; and the 2001 award to William S. Knowles and K. Barry Sharpless for their work on asymmetric synthesis. The outcomes of these discoveries are leading science in the twenty-first century. The use of PCR analysis has contributed to the development of forensic science. The discovery C60 and related carbon compounds, known as nanotubes, is leading to ideas in drug delivery methods and the storage of hydrogen and carbon dioxide. The computational tools developed by Pople and Kohn are being used to assist scientists in analyzing and designing experiments. Femtosecond chemistry is providing insight into how bonds are made and broken as a chemical reaction proceeds. Heeger and MacDiarmid's work has led to what is now known as plastic electronics—devices made of conducting polymers, ranging from light-emitting diodes to flat panel displays. The work by Knowles and Sharpless has provided organic chemists with the tools to synthesize compounds that contain chirality or handedness. This has had a tremendous impact on the synthesis of drugs, agrochemicals, and petrochemicals.

Bibliography

Brock, William H. The Norton History of Chemistry. New York: Norton, 1993.

———. The Chemical Tree: A History of Chemistry. New York: Norton, 2000.

Greenberg, Arthur. A Chemical History Tour: Picturing Chemistry from Alchemy to Modern Molecular Science. New York: Wiley, 2000.

Servos, John W. Physical Chemistry from Ostwald to Pauling: The Making of Science in America. Princeton, N.J.: Princeton University Press, 1990.

—Jeffrey D. Madura

Columbia Encyclopedia: chemistry

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chemistry, branch of science concerned with the properties, composition, and structure of substances and the changes they undergo when they combine or react under specified conditions.

Branches of Chemistry

Chemistry can be divided into branches according to either the substances studied or the types of study conducted. The primary division of the first type is between inorganic chemistry and organic chemistry. Divisions of the second type are physical chemistry and analytical chemistry.

The original distinction between organic and inorganic chemistry arose as chemists gradually realized that compounds of biological origin were quite different in their general properties from those of mineral origin; organic chemistry was defined as the study of substances produced by living organisms. However, when it was discovered in the 19th cent. that organic molecules can be produced artificially in the laboratory, this definition had to be abandoned. Organic chemistry is most simply defined as the study of the compounds of carbon. Inorganic chemistry is the study of chemical elements and their compounds (with the exception of carbon compounds).

Physical chemistry is concerned with the physical properties of materials, such as their electrical and magnetic behavior and their interaction with electromagnetic fields. Subcategories within physical chemistry are thermochemistry, electrochemistry, and chemical kinetics. Thermochemistry is the investigation of the changes in energy and entropy that occur during chemical reactions and phase transformations (see states of matter). Electrochemistry concerns the effects of electricity on chemical changes and interconversions of electric and chemical energy such as that in a voltaic cell. Chemical kinetics is concerned with the details of chemical reactions and of how equilibrium is reached between the products and reactants.

Analytical chemistry is a collection of techniques that allows exact laboratory determination of the composition of a given sample of material. In qualitative analysis all the atoms and molecules present are identified, with particular attention to trace elements. In quantitative analysis the exact weight of each constituent is obtained as well. Stoichiometry is the branch of chemistry concerned with the weights of the chemicals participating in chemical reactions. See also chemical analysis.

History of Chemistry

The earliest practical knowledge of chemistry was concerned with metallurgy, pottery, and dyes; these crafts were developed with considerable skill, but with no understanding of the principles involved, as early as 3500 B.C. in Egypt and Mesopotamia. The basic ideas of element and compound were first formulated by the Greek philosophers during the period from 500 to 300 B.C. Opinion varied, but it was generally believed that four elements (fire, air, water, and earth) combined to form all things. Aristotle's definition of a simple body as "one into which other bodies can be decomposed and which itself is not capable of being divided" is close to the modern definition of element.

About the beginning of the Christian era in Alexandria, the ancient Egyptian industrial arts and Greek philosophical speculations were fused into a new science. The beginnings of chemistry, or alchemy, as it was first known, are mingled with occultism and magic. Interests of the period were the transmutation of base metals into gold, the imitation of precious gems, and the search for the elixir of life, thought to grant immortality. Muslim conquests in the 7th cent. A.D. diffused the remains of Hellenistic civilization to the Arab world. The first chemical treatises to become well known in Europe were Latin translations of Arabic works, made in Spain c.A.D. 1100; hence it is often erroneously supposed that chemistry originated among the Arabs. Alchemy developed extensively during the Middle Ages, cultivated largely by itinerant scholars who wandered over Europe looking for patrons.

Evolution of Modern Chemistry

In the hands of the "Oxford Chemists" (Robert Boyle, Robert Hooke, and John Mayow) chemistry began to emerge as distinct from the pseudoscience of alchemy. Boyle (1627-91) is often called the founder of modern chemistry (an honor sometimes also given Antoine Lavoisier, 1743-94). He performed experiments under reduced pressure, using an air pump, and discovered that volume and pressure are inversely related in gases (see gas laws). Hooke gave the first rational explanation of combustion-as combination with air-while Mayow studied animal respiration. Even as the English chemists were moving toward the correct theory of combustion, two Germans, J. J. Becher and G. E. Stahl, introduced the false phlogiston theory of combustion, which held that the substance phlogiston is contained in all combustible bodies and escapes when the bodies burn.

The discovery of various gases and the analysis of air as a mixture of gases occurred during the phlogiston period. Carbon dioxide, first described by J. B. van Helmont and rediscovered by Joseph Black in 1754, was originally called fixed air. Hydrogen, discovered by Boyle and carefully studied by Henry Cavendish, was called inflammable air and was sometimes identified with phlogiston itself. Cavendish also showed that the explosion of hydrogen and oxygen produces water. C. W. Scheele found that air is composed of two fluids, only one of which supports combustion. He was the first to obtain pure oxygen (1771-73), although he did not recognize it as an element. Joseph Priestley independently discovered oxygen by heating the red oxide of mercury with a burning glass; he was the last great defender of the phlogiston theory.

The work of Priestley, Black, and Cavendish was radically reinterpreted by Lavoisier, who did for chemistry what Newton had done for physics a century before. He made no important new discoveries of his own; rather, he was a theoretician. He recognized the true nature of combustion, introduced a new chemical nomenclature, and wrote the first modern chemistry textbook. He erroneously believed that all acids contain oxygen.

Impact of the Atomic Theory

The assumption that compounds were of definite composition was implicit in 18th-century chemistry. J. L. Proust formally stated the law of constant proportions in 1797. C. L. Berthollet opposed this law, holding that composition depended on the method of preparation. The issue was resolved in favor of Proust by John Dalton's atomic theory (1808). The atomic theory goes back to the Greeks, but it did not prove fruitful in chemistry until Dalton ascribed relative weights to the atoms of chemical elements. Electrochemical theories of chemical combinations were developed by Humphry Davy and J. J. Berzelius. Davy discovered the alkali metals by passing an electric current through their molten oxides. Michael Faraday discovered that a definite quantity of charge must flow in order to deposit a given weight of material in solution. Amedeo Avogadro introduced the hypothesis that equal volumes of gases at the same pressure and temperature contain the same number of molecules.

William Prout suggested that as all elements seemed to have atomic weights that were multiples of the atomic weight of hydrogen, they could all be in some way different combinations of hydrogen atoms. This contributed to the concept of the periodic table of the elements, the culmination of a long effort to find regular, systematic properties among the elements. Periodic laws were put forward almost simultaneously and independently by J. L. Meyer in Germany and D. I. Mendeleev in Russia (1869). An early triumph of the new theory was the discovery of new elements that fit the empty spaces in the table. William Ramsay's discovery, in collaboration with Lord Rayleigh, of argon and other inert gases in the atmosphere extended the periodic table

Organic Chemistry and the Modern Era

Organic chemistry developed extensively in the 19th cent., prompted in part by Friedrich Wohler's synthesis of urea (1828), which disproved the belief that only living organisms could produce organic molecules. Other important organic chemists include Justus von Liebig, C. A. Wurtz, and J. B. Dumas. In 1852 Edward Frankland introduced the idea of valency (see valence), and in 1858 F. A. Kekule showed that carbon atoms are tetravalent and are linked together in chains. Kekule's ring structure for benzene opened the way to modern theories of organic chemistry. Henri Louis Le Châtelier, J. H. van't Hoff, and Wilhelm Ostwald pioneered the application of thermodynamics to chemistry. Further contributions were the phase rule of J. W. Gibbs, the ionization equilibrium theory of S. A. Arrhenius, and the heat theorem of Walther Nernst. Ernst Fischer's work on the amino acids marks the beginning of molecular biology.

At the end of the 19th cent., the discovery of the electron by J. J. Thomson and of radioactivity by A. E. Becquerel revealed the close connection between chemistry and physics. The work of Ernest Rutherford, H. G. J. Moseley, and Niels Bohr on atomic structure (see atom) was applied to molecular structures. G. N. Lewis, Irving Langmuir, and Linus Pauling developed the electronic theory of chemical bonds, directed valency, and molecular orbitals (see molecular orbital theory). Transmutation of the elements, first achieved by Rutherford, has led to the creation of elements not found in nature; in work pioneered by Glenn Seaborg elements heavier than uranium have been produced. With the rapid development of polymer chemistry after World War II a host of new synthetic fibers and materials have been added to the market. A fuller understanding of the relation between the structure of molecules and their properties has allowed chemists to tailor predictively new materials to meet specific needs.

Bibliography

See I. Asimov, A Short History of Chemistry (1965); D. A. McQuarrie and P. A. Rock, General Chemistry (1984); L. Pauling, General Chemistry (3d ed. 1991); R. C. Weast, ed., CRC Handbook of Chemistry and Physics (published annually).

History 1450-1789: Chemistry

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The history of early modern chemistry, understood as a body of ideas and practices related to compounding and decomposing material substances, takes us to alchemy and apothecary laboratories, artisans' workshops, metallurgists and manufacturers, scientific societies, arsenals, royal courts, and public squares. It should not be understood in terms of the victory of scientific theory over arcane beliefs, but of the changing employment of its various technologies and the contexts in and by which they were legitimized.

Material and Bodily Technology

Chemistry's material technology—that is, its instruments and laboratory equipment—remained stable throughout most of the period, but was augmented by precision-oriented apparatus in the second half of the eighteenth century as the study of heat and gases, along with early industrial innovations, redirected chemical investigations. Increasingly accurate measuring devices helped bring about standardization in manufacturing ventures (e.g. Josiah Wedgwood's pottery works) while feeding debates over how to organize chemistry as an investigative enterprise. Should the heterogeneous chemical world be disciplined by analyzing qualitative or quantitative data?

The way chemical operators and investigators used their own bodies was part of this historical development and debate. As long as chemical determination rested on examining colors, smells, tastes and textures, the human senses served as crucial chemical instruments. As experimental claims increasingly relied on precise measurements by the late eighteenth century (a hallmark of the chemical revolution), sense evidence became "subjective" and, hence, a questionable foundation for proof. Chemists continued to rely on their senses, but proof became increasingly a matter of quantitative determination.

Theory and Practice

The question of what constituted a primary chemical element was not a part of practical chemists' daily routine. Neither, prior to the late eighteenth century, was there a direct correlation between one's theoretical views and how one actually carried out chemical procedures, which can be seen by examining the impact of the mechanical philosophy on chemistry. Textbook writers such as Nicolas Lémery (1645–1715) attributed a substance's qualities to the shape of particles that composed it. But authors left such explanations behind when dealing with actual chemical operations. Robert Boyle (1627–1691), often labeled a mechanical philosopher, made a bigger impact on chemistry through his interests in practical knowledge and alchemy. Even Isaac Newton's (1642–1727) mechanism, which married particles to short-range forces, hardly touched chemical practice—although theorists such as Georges-Louis Leclerc de Buffon (1707–1788) hoped chemical attraction (affinities) could be explained mathematically with Newtonian forces. Working chemists continued to learn their trade through apprenticeship and to be guided by practical recipes. Acquiring tacit knowledge and practical skills, then, were certainly as important for the historical development of chemistry as theoretical knowledge.

It is, however, historically important that matter theory became linked to chemical research in an increasingly instrumental way by the eighteenth century. Paracelsus (1493–1541), who argued for the chemical foundation of medicine (iatrochemistry), claimed that Aristotle's four elements appeared in bodies as mercury, sulfur, and salt. Mercury was the principle of volatility and fusibility, sulfur of inflammability, and salt of incombustibility. Therefore, chemists might recognize a compound not only as heavy or wet, but also as liable to specific chemical processes.

Johann Joachim Becher (1635–1682) substituted three categories of earth for Paracelsus's principles and explained material change largely in terms of their combination with and release from compounds through processes such as combustion. His student George Ernst Stahl (1660–1734) further codified Becher's work, giving the name "phlogiston" (from the Greek verb "to inflame") to Becher's terra pinguis (the sulfur of inflammability) and teaching that phlogiston's presence was responsible for characteristics including metallicity, color, and inflammability. In France, the influential chemistry lecturer Guillaume François Rouelle (1703–1770) popularized the idea of phlogiston, associating it with fire. Others such as Joseph Priestley (1733–1804) identified it variously with electricity and hydrogen. Phlogiston was used to explain phenomena including combustion, calcination, and the quality of air, thereby organizing a number of research activities under a set of interconnecting theories and emphasizing the potential reversibility of chemical processes.

Others began considering the Aristotelian elements as material instruments. Stephen Hales (1677–1761) focused on the expansion of air and the way in which it could become "fixed" in bodies. Herman Boerhaave (1668–1738) went further, organizing his chemistry lectures largely around the investigative consequences of considering earth, water, air, and fire as instruments that afforded specific chemical processes. A Newtonian by public pronouncement, Boerhaave actually did much more to stimulate chemical research by focusing on the reactive effects of these elemental instruments. He related fire (the substance of heat) to the primary processes of expansion and repulsion. He presented air and water as providing containers in which other particles were suspended. It wasn't long before these "instruments" themselves were subjected to chemical analysis, as investigators sought to understand whether their "instrumental" presence was chemically passive or active. Research in the second half of the eighteenth century was marked by investigations of newly discovered gases (qualitatively distinct "airs"), the role of heat, and, in the 1780s, the composition of water.

Literary Technology

Chemical theory and instrumental research practices were also linked in the way chemical knowledge came to be organized nomenclaturally and in analytical tables (chemistry's literary technology). Related to the heritage of alchemy and the various contexts in which chemical substances were discovered and used, chemical nomenclature was traditionally a colorfully unsystematic affair. Growing interest in chemical research in the second half of the eighteenth century, especially the investigation of a number of new "airs," led chemists to consider nomenclatural reform. Standard conventions for naming new substances would allow researchers from various communities to communicate. In 1787 Antoine Laurent Lavoisier (1743–1794), Louis Bernard Guyton de Morveau (1737–1816), Antoine François Fourcroy (1755–1809), and Claude Simon Berthollet (1748–1822) revamped chemistry's nomenclature totally, enunciating in their Méthode de nomenclature chimique a revolutionary way to structure chemistry's investigative knowledge and practices.

Oxygen's discovery and naming provides a good example. Recognized in the 1770s as a distinct "air" responsible for combustion, supporting respiration, and the process of calcination, it was variously named the "purest part of air," "fire air," "eminently respirable air," and "dephlogisticated air." Lavoisier focused on what he considered its most far-reaching characteristic and argued that it should be called "oxygen," the "generator" of acids. Not only did he use oxygen's causal properties to argue against the existence of phlogiston, he named the substance in a way that simultaneously reflected how the relation between these properties ought to be understood and how chemists ought to pursue future research.

Traditionally, the secretive nature of many alchemical and artisanal practices had combined with chemistry's lack of institutional and disciplinary unity to work against the development of a public, systematic means of recording compositional data. This began changing when Étienne François Geoffroy (1672–1731) presented his "Table of the different relationships observed between different substances" to the French Academy of Sciences in 1718. Recording and publishing these relationships, often called affinities, provided a handy way for chemists to share and expand empirical knowledge without having to agree on their theoretical explanation. As the century progressed, affinity and solvent tables became more sophisticated (recording, for example, how relations were observed), leading chemists to hope that their field might thereby gain the certainty of a scientific discipline. As was true with nomenclatural reform, this was largely achieved by Lavoisier and his colleagues, with revolutionary results. Lavoisier's 1789 textbook Traitéélémentaire de chimie included tables whose structures redirected research along the same lines as chemistry's new nomenclature.

Lavoisier began his textbook by arguing that humans live in a Condillacian world; chemists should therefore build their discipline on a foundation of sensible facts. Chemistry's nomenclature should express only what chemists actively observed; its basic elements should be defined by laboratory procedures. In fact, Lavoisier began his "table of simple substances" with five elements that could never be isolated, but which he made responsible for fundamental chemical processes. Oxygen "generates" acidity, hydrogen "generates" water. Caloric, the substance of heat, interacts with chemical affinities to regulate composition and decomposition. In place of affinity and solvent tables, Lavoisier filled his textbook with tables that simultaneously recorded and predicted the combinatorial powers of elements such as oxygen. Together they formed an integrated research program intended to discipline chemistry.

Chemistry's Instrumentalization

Lavoisier's laboratory practices reflected what appeared on the pages of his book, the last third of which treated laboratory instruments. If primary elements couldn't be isolated, Lavoisier argued that their active presence could be quantitatively traced. Unmeasurable phlogiston was out, precision balances were in, as seen in his proof that water is compounded of hydrogen and oxygen. Affinities could not yet be quantified, but the effect of caloric on composition and decomposition could be quantitatively inferred by the melting of ice in an ice calorimeter—an instrument designed by Lavoisier. In general, nomenclature, instrumental theory, and measurement provided a research program for future chemists, in terms of both questions and methods for resolving them.

This culmination of chemistry's instrumentalization was, arguably, the essence of the chemical revolution. Whether others adopted Lavoisier's theories or followed the specifics of his research proposals, the modern discipline of chemistry was permanently marked by the instrumental bounds he prescibed.

Bibliography

Bensaude-Vincent, Bernadette. Lavoisier. Memoires d'une révolution. Paris, 1993.

Golinski, Jan. Science as Public Culture: Chemistry and Enlightenment in Britain 1760–1820. Cambridge, U.K., 1992.

Hannaway, Owen. The Chemist and the Word: The Didactic Origins of Chemistry. Baltimore, 1985.

Holmes, Frederick Lawrence. Eighteenth-Century Chemistry as an Investigative Enterprise. Berkeley, 1989.

Roberts, Lissa. "The Death of the Sensuous Chemist: the 'New' Chemistry and the Transformation of Sensuous Technology." Studies in History and Philosophy of Science 26 (1995): 503–529.

——. "Setting the Table: The Disciplinary Development of Eighteenth-Century Chemistry as Read through the Changing Structure of its Tables." In The Literary Structure of Scientific Argument, edited by Peter Dear, pp. 99–132. Philadelphia, 1991.

—LISSA ROBERTS

Quotes About: Chemistry

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Quotes:

"I feel like a white granular mass of amorphous crystals -- my formula appears to be isomeric with Spasmotoxin. My aurochloride precipitates into beautiful prismatic needles. My Platinochloride develops octahedron crystals, -- with a fine blue florescence. My physiological action is not indifferent. One millionth of a grain injected under the skin of a frog produced instantaneous death accompanied by an orange blossom odor." - Lafcadio Hearn

"For me chemistry represented an indefinite cloud of future potentialities which enveloped my life to come in black volutes torn by fiery flashes, like those which had hidden Mount Sinai. Like Moses, from that cloud I expected my law, the principle of order in me, around me, and in the world. I would watch the buds swell in spring, the mica glint in the granite, my own hands, and I would say to myself: I will understand this, too, I will understand everything." - Primo Levi

"There's nothing colder than chemistry." - Anita Loos

Wikipedia: Chemistry

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For other uses, see Chemistry (disambiguation).

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions.

Chemistry is the study of interactions of chemical substances with one another and energy.

Chemistry (from Arabic:الكيم Latinized: chem (kēme), meaning "earth")^[1] is the science concerned with the composition, behavior, structure, and properties of matter, as well as the changes it undergoes during chemical reactions.^[2] It is a physical science for studies of various atoms, molecules, crystals and other aggregates of matter whether in isolation or combination, which incorporates the concepts of energy and entropy in relation to the spontaneity of chemical processes. Modern chemistry evolved out of alchemy and began to develop into its modern form through the 10th Century Arab world and following the chemical revolution (1773).

Disciplines within chemistry are traditionally grouped by the type of matter being studied or the kind of study. These include inorganic chemistry, the study of inorganic matter; organic chemistry, the study of organic matter; biochemistry, the study of substances found in biological organisms; physical chemistry, the energy related studies of chemical systems at macro, molecular and submolecular scales; analytical chemistry, the analysis of material samples to gain an understanding of their chemical composition and structure. Many more specialized disciplines have emerged in recent years, e.g. neurochemistry the chemical study of the nervous system (see subdisciplines).

Summary

Chemistry is the scientific study of interaction of chemical substances^[3] that are constituted of atoms or the subatomic particles: protons, electrons and neutrons.^[4] Atoms combine to produce molecules or crystals. Chemistry is often called "the central science" because it connects the other natural sciences such as astronomy, physics, material science, biology, and geology.^[5]^[6]

The genesis of chemistry can be traced to certain practices, known as alchemy, which had been practiced for several millennia in various parts of the world, particularly the Middle East.^[7]

The structure of objects we commonly use and the properties of the matter we commonly interact with, are a consequence of the properties of chemical substances and their interactions. For example, steel is harder than iron because its atoms are bound together in a more rigid crystalline lattice; wood burns or undergoes rapid oxidation because it can react spontaneously with oxygen in a chemical reaction above a certain temperature; sugar and salt dissolve in water because their molecular/ionic properties are such that dissolution is preferred under the ambient conditions.

The transformations that are studied in chemistry are a result of interaction either between different chemical substances or between matter and energy. Traditional chemistry involves study of interactions between substances in a chemistry laboratory using various forms of laboratory glassware.

Laboratory, Institute of Biochemistry, University of Cologne

A chemical reaction is a transformation of some substances into one or more other substances.^[8] It can be symbolically depicted through a chemical equation. The number of atoms on the left and the right in the equation for a chemical transformation is most often equal. The nature of chemical reactions a substance may undergo and the energy changes that may accompany it are constrained by certain basic rules, known as chemical laws.

Energy and entropy considerations are invariably important in almost all chemical studies. Chemical substances are classified in terms of their structure, phase as well as their chemical compositions. They can be analyzed using the tools of chemical analysis, e.g. spectroscopy and chromatography.

Chemistry is an integral part of the science curriculum both at the high school as well as the early college level. At these levels, it is often called "general chemistry" which is an introduction to a wide variety of fundamental concepts that enable the student to acquire tools and skills useful at the advanced levels, whereby chemistry is invariably studied in any of its various sub-disciplines. Scientists, engaged in chemical research are known as chemists.^[9] Most chemists specialize in one or more sub-disciplines.

History

Main article: History of chemistry

Ancient Egyptians pioneered the art of synthetic "wet" chemistry up to 4,000 years ago.^[10] By 1000 BC ancient civilizations were using technologies that formed the basis of the various branches of chemistry such as; extracting metal from their ores, making pottery and glazes, fermenting beer and wine, making pigments for cosmetics and painting, extracting chemicals from plants for medicine and perfume, making cheese, dying cloth, tanning leather, rendering fat into soap, making glass, and making alloys like bronze.

The genesis of chemistry can be traced to the widely observed phenomenon of burning that led to metallurgy—the art and science of processing ores to get metals (e.g. metallurgy in ancient India). The greed for gold led to the discovery of the process for its purification, even though the underlying principles were not well understood—it was thought to be a transformation rather than purification. Many scholars in those days thought it reasonable to believe that there exist means for transforming cheaper (base) metals into gold. This gave way to alchemy and the search for the Philosopher's Stone which was believed to bring about such a transformation by mere touch.^[11]

Greek atomism dates back to 440 BC, as what might be indicated by the book De Rerum Natura (The Nature of Things)^[12] written by the Roman Lucretius^[13] in 50 BC. Much of the early development of purification methods is described by Pliny the Elder in his Naturalis Historia.

The earliest pioneers of Chemistry, and inventors of the modern scientific method, were medieval Arab and Persian scholars. They introduced precise observation and controlled experimentation into the field and discovered numerous Chemical substances.^[14] The most influential Muslim chemists were Geber (d. 815), al-Kindi (d. 873), al-Razi (d. 925), al-Biruni (d. 1048) and Alhazen (d. 1039).^[15] The works of Geber became more widely known in Europe through Latin translations by a pseudo-Geber in 14th century Spain, who also wrote some of his own books under the pen name "Geber". The contribution of Indian alchemists and metallurgists in the development of chemistry was also quite significant.^[16]

The emergence of chemistry in Europe was primarily due to the recurrent incidence of the plague and blights there during the so called Dark Ages. This gave rise to a need for medicines. It was thought that there exists a universal medicine called the Elixir of Life that can cure all diseases, but like the Philosopher's Stone, it was never found.

For some practitioners, alchemy was an intellectual pursuit, over time, they got better at it. Paracelsus (1493–1541), for example, rejected the 4-elemental theory and with only a vague understanding of his chemicals and medicines, formed a hybrid of alchemy and science in what was to be called iatrochemistry. Similarly, the influences of philosophers such as Sir Francis Bacon (1561–1626) and René Descartes (1596–1650), who demanded more rigor in mathematics and in removing bias from scientific observations, led to a scientific revolution. In chemistry, this began with Robert Boyle (1627–1691), who came up with an equation known as Boyle's Law about the characteristics of gaseous state.^[17] Chemistry indeed came of age when Antoine Lavoisier (1743–1794), developed the theory of Conservation of mass in 1783; and the development of the Atomic Theory by John Dalton around 1800. The Law of Conservation of Mass resulted in the reformulation of chemistry based on this law and the oxygen theory of combustion, which was largely based on the work of Lavoisier. Lavoisier's fundamental contributions to chemistry were a result of a conscious effort to fit all experiments into the framework of a single theory. He established the consistent use of the chemical balance, used oxygen to overthrow the phlogiston theory, and developed a new system of chemical nomenclature and made contribution to the modern metric system. Lavoisier also worked to translate the archaic and technical language of chemistry into something that could be easily understood by the largely uneducated masses, leading to an increased public interest in chemistry. All these advances in chemistry led to what is usually called the chemical revolution. The contributions of Lavoisier led to what is now called modern chemistry—the chemistry that is studied in educational institutions all over the world. It is because of these and other contributions that Antoine Lavoisier is often celebrated as the "Father of Modern Chemistry".^[18] The later discovery of Friedrich Wöhler that many natural substances, organic compounds, can indeed be synthesized in a chemistry laboratory also helped the modern chemistry to mature from its infancy.^[19]

The discovery of the chemical elements has a long history from the days of alchemy and culminating in the creation of the periodic table of the chemical elements by Dmitri Mendeleev (1834–1907)^[20] and later discoveries of some synthetic elements.

Etymology

Main article: Chemistry (etymology)

The word chemistry comes from the earlier study of alchemy, which is a set of practices that encompasses elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism and medicine. Alchemy is commonly thought of as the quest to turn lead or another common starting material into gold.^[21] As to the origin of the word "alchemy" the question is a debatable one; it certainly can be traced back to the Greeks, and some, following E. Wallis Budge, have also asserted Egyptian origins. Many believe that the word "alchemy" is derived from the word Chemi or Kimi, which is the name of Egypt in Egyptian.^[22]^[23]^[24] The word was subsequently borrowed by the Greeks, and from the Greeks by the Arabs when they occupied Alexandria (Egypt) in the 7th century. The Arabs added the Arabic definite article "al" to the word, resulting in the word الكيمياء "al-kīmiyā", from which is derived the old French alkemie. A tentative outline is as follows:

Egyptian alchemy [3,000 BCE – 400 BCE], formulate early "element" theories such as the Ogdoad.
Greek alchemy [332 BCE – 642 CE], the Greek king Alexander the Great conquers Egypt and founds Alexandria, having the world's largest library, where scholars and wise men gather to study.
Arab alchemy [642 CE – 1200], the Arabs invade Alexandria; Jabir is the main chemist
European alchemy [1300 – present], Pseudo-Geber builds on Arabic chemistry
Chemistry [1661], Boyle writes his classic chemistry text The Sceptical Chymist
Chemistry [1787], Lavoisier writes his classic Elements of Chemistry
Chemistry [1803], Dalton publishes his Atomic Theory

Thus, an alchemist was called a 'chemist' in popular speech, and later the suffix "-ry" was added to this to describe the art of the chemist as "chemistry".

Definitions

In retrospect, the definition of chemistry seems to invariably change per decade, as new discoveries and theories add to the functionality of the science. Shown below are some of the standard definitions used by various noted chemists:

Alchemy (330) – the study of the composition of waters, movement, growth, embodying, disembodying, drawing the spirits from bodies and bonding the spirits within bodies (Zosimos).^[25]
Chymistry (1661) – the subject of the material principles of mixt bodies (Boyle).^[26]
Chymistry (1663) – a scientific art, by which one learns to dissolve bodies, and draw from them the different substances on their composition, and how to unite them again, and exalt them to a higher perfection (Glaser).^[27]
Chemistry (1730) – the art of resolving mixt, compound, or aggregate bodies into their principles; and of composing such bodies from those principles (Stahl).^[28]
Chemistry (1837) – the science concerned with the laws and effects of molecular forces (Dumas).^[29]
Chemistry (1947) – the science of substances: their structure, their properties, and the reactions that change them into other substances (Pauling).^[30]
Chemistry (1998) – the study of matter and the changes it undergoes (Chang).^[31]

Basic concepts

Several concepts are essential for the study of chemistry; some of them are:^[32]

Atom

Main article: Atom

An atom is the basic unit of chemistry. It consists of a positively charged core (the atomic nucleus) which contains protons and neutrons, and which maintains a number of electrons to balance the positive charge in the nucleus. The atom is also the smallest entity that can be envisaged to retain some of the chemical properties of the element, such as electronegativity, ionization potential, preferred oxidation state(s), coordination number, and preferred types of bonds to form (e.g., metallic, ionic, covalent).

Element

Main article: Chemical element

The concept of chemical element is related to that of chemical substance. A chemical element is characterized by a particular number of protons in the nuclei of its atoms. This number is known as the atomic number of the element. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon, and all atoms with 92 protons in their nuclei are atoms of the element uranium. However, several isotopes of an element, that differ from one another in the number of neutrons present in the nucleus, may exist.

The most convenient presentation of the chemical elements is in the periodic table of the chemical elements, which groups elements by atomic number. Due to its ingenious arrangement, groups, or columns, and periods, or rows, of elements in the table either share several chemical properties, or follow a certain trend in characteristics such as atomic radius, electronegativity, etc. Lists of the elements by name, by symbol, and by atomic number are also available.

Compound

Main article: Chemical compound

A compound is a substance with a particular ratio of atoms of particular chemical elements which determines its composition, and a particular organization which determines chemical properties. For example, water is a compound containing hydrogen and oxygen in the ratio of two to one, with the oxygen atom between the two hydrogen atoms, and an angle of 104.5° between them. Compounds are formed and interconverted by chemical reactions.

Substance

Main article: Chemical substance

A chemical substance is a kind of matter with a definite composition and set of properties.^[33] Strictly speaking, a mixture of compounds, elements or compounds and elements is not a chemical substance, but it may be called a chemical. Most of the substances we encounter in our daily life are some kind of mixture; for example: air, alloys, biomass, etc.

Nomenclature of substances is a critical part of the language of chemistry. Generally it refers to a system for naming chemical compounds. Earlier in the history of chemistry substances were given name by their discoverer, which often led to some confusion and difficulty. However, today the IUPAC system of chemical nomenclature allows chemists to specify by name specific compounds amongst the infinite variety of possible chemicals. The standard nomenclature of chemical substances is set by the International Union of Pure and Applied Chemistry (IUPAC). There are well-defined systems in place for naming chemical species. Organic compounds are named according to the organic nomenclature system.^[34] Inorganic compounds are named according to the inorganic nomenclature system.^[35] In addition the Chemical Abstracts Service has devised a method to index chemical substance. In this scheme each chemical substance is identifiable by a numeric number known as CAS registry number.

Molecule

Main article: Molecule

A molecule is the smallest indivisible portion, besides an atom, of a pure chemical substance that has its unique set of chemical properties, that is, its potential to undergo a certain set of chemical reactions with other substances. Molecules can exist as electrically neutral units unlike ions. Molecules are typically a set of atoms bound together by covalent bonds, such that the structure is electrically neutral and all valence electrons are paired with other electrons either in bonds or in lone pairs.

A molecular structure depicts the bonds and relative positions of atoms in a molecule such as that in Paclitaxel shown here

One of the main characteristic of a molecule is its geometry often called its structure. While the structure of diatomic, triatomic or tetra atomic molecules may be trivial, (linear, angular pyramidal etc.) the structure of polyatomic molecules, that are constituted of more than six atoms (of several elements) can be crucial for its chemical nature.

Mole

Main article: Mole (unit)

A mole is the amount of a substance that contains as many elementary entities (atoms, molecules or ions) as there are atoms in 0.012 kilogram (or 12 grams) of carbon-12, where the carbon-12 atoms are unbound, at rest and in their ground state.^[36] This number is known as the Avogadro constant, and is determined empirically. The currently accepted value is 6.02214179(30) × 10²³ mol^-1 (2007 CODATA). The best way to understand the meaning of the term "mole" is to compare it to terms such as dozen. Just as one dozen is equal to 12, one mole is equal to 6.02214179(30) × 10²³. The term is used because it is much easier to say, for example, 1 mole of carbon atoms, than it is to say 6.02214179(30) × 10²³ carbon atoms. Likewise, we can describe the number of entities as a multiple or fraction of 1 mole, e.g. 2 mole or 0.5 moles. Mole is an absolute number (having no units) and can describe any type of elementary object, although the mole's use is usually limited to measurement of subatomic, atomic, and molecular structures.

The number of moles of a substance in one liter of a solution is known as its molarity. Molarity is the common unit used to express the concentration of a solution in physical chemistry.

Ions and salts

Main article: Ion

An ion is a charged species, an atom or a molecule, that has lost or gained one or more electrons. Positively charged cations (e.g. sodium cation Na⁺) and negatively charged anions (e.g. chloride Cl⁻) can form a crystalline lattice of neutral salts (e.g. sodium chloride NaCl). Examples of polyatomic ions that do not split up during acid-base reactions are hydroxide (OH⁻) and phosphate (PO₄³⁻).

Ions in the gaseous phase is often known as plasma.

Acidity and basicity

Main article: Acid

A substance can often be classified as an acid or a base. This is often done on the basis of a particular kind of reaction, namely the exchange of protons between chemical compounds. However, an extension to this mode of classification was brewed up by the American chemist, Gilbert Newton Lewis; in this mode of classification the reaction is not limited to those occurring in an aqueous solution, thus is no longer limited to solutions in water. According to concept as per Lewis, the crucial things being exchanged are charges^[37]. There are several other ways in which a substance may be classified as an acid or a base, as is evident in the history of this concept ^[38]

Phase

Main article: Phase (matter)

In addition to the specific chemical properties that distinguish different chemical classifications chemicals can exist in several phases. For the most part, the chemical classifications are independent of these bulk phase classifications; however, some more exotic phases are incompatible with certain chemical properties. A phase is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as pressure or temperature. Physical properties, such as density and refractive index tend to fall within values characteristic of the phase. The phase of matter is defined by the phase transition, which is when energy put into or taken out of the system goes into rearranging the structure of the system, instead of changing the bulk conditions.

Sometimes the distinction between phases can be continuous instead of having a discrete boundary, in this case the matter is considered to be in a supercritical state. When three states meet based on the conditions, it is known as a triple point and since this is invariant, it is a convenient way to define a set of conditions.

The most familiar examples of phases are solids, liquids, and gases. Many substances exhibit multiple solid phases. For example, there are three phases of solid iron (alpha, gamma, and delta) that vary based on temperature and pressure. A principal difference between solid phases is the crystal structure, or arrangement, of the atoms. Another phase commonly encountered in the study of chemistry is the aqueous phase, whihch is the state of substances dissolved in aqueous solution (that is, in water). Less familiar phases include plasmas, Bose-Einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of magnetic materials. While most familiar phases deal with three-dimensional systems, it is also possible to define analogs in two-dimensional systems, which has received attention for its relevance to systems in biology.

Redox

Main article: Redox

It is a concept related to the ability of atoms of various substances to lose or gain electrons. Substances that have the ability to oxidize other substances are said to be oxidative and are known as oxidizing agents, oxidants or oxidizers. An oxidant removes electrons from another substance. Similarly, substances that have the ability to reduce other substances are said to be reductive and are known as reducing agents, reductants, or reducers. A reductant transfers electrons to another substance, and is thus oxidized itself. And because it "donates" electrons it is also called an electron donor. Oxidation and reduction properly refer to a change in oxidation number—the actual transfer of electrons may never occur. Thus, oxidation is better defined as an increase in oxidation number, and reduction as a decrease in oxidation number.

Chemical bond

Main article: Chemical bond

Electron atomic and molecular orbitals

A chemical bond is a concept for understanding how atoms stick together in molecules. It may be visualized as the multipole balance between the positive charges in the nuclei and the negative charges oscillating about them.^[39] More than simple attraction and repulsion, the energies and distributions characterize the availability of an electron to bond to another atom. These potentials create the interactions which hold atoms together in molecules or crystals. In many simple compounds, Valence Bond Theory, the Valence Shell Electron Pair Repulsion model (VSEPR), and the concept of oxidation number can be used to predict molecular structure and composition. Similarly, theories from classical physics can be used to predict many ionic structures. With more complicated compounds, such as metal complexes, valence bond theory fails and alternative approaches, primarily based on principles of quantum chemistry such as the molecular orbital theory, are necessary. See diagram on electronic orbitals.

Chemical reaction

Main article: Chemical reaction

Chemical reaction is a concept related to the transformation of a chemical substance through its interaction with another, or as a result of its interaction with some form of energy. A chemical reaction may occur naturally or carried out in a laboratory by chemists in specially designed vessels which are often laboratory glassware. It can result in the formation or dissociation of molecules, that is, molecules breaking apart to form two or more smaller molecules, or rearrangement of atoms within or across molecules. Chemical reactions usually involve the making or breaking of chemical bonds. Oxidation, reduction, dissociation, acid-base neutralization and molecular rearrangement are some of the commonly used kinds of chemical reactions.

A chemical reaction can be symbolically depicted through a chemical equation. While in a non-nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons.^[40]

The sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism. A chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. Many reaction intermediates with variable stability can thus be envisaged during the course of a reaction. Reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. Many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. Several empirical rules, like the Woodward-Hoffmann rules often come handy while proposing a mechanism for a chemical reaction.

A stricter definition is that "a chemical reaction is a process that results in the interconversion of chemical species".^[41] Under this definition, a chemical reaction may be an elementary reaction or a stepwise reaction. An additional caveat is made, in that this definition includes cases where the interconversion of conformers is experimentally observable. Such detectable chemical reactions normally involve sets of molecular entities as indicated by this definition, but it is often conceptually convenient to use the term also for changes involving single molecular entities (i.e. 'microscopic chemical events').

Energy

Main article: Energy

In the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. Since a chemical transformation is accompanied by a change in one or more of these kinds of structure, it is invariably accompanied by an increase or decrease of energy of the substances involved. Some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light; thus the products of a reaction may have more or less energy than the reactants. A reaction is said to be exothermic if the final state is lower on the energy scale than the initial state; in the case of endothermic reactions the situation is otherwise.

Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. The speed of a chemical reaction (at given temperature T) is related to the activation energy E, by the Boltzmann's population factor $e - E / k T$ - that is the probability of molecule to have energy greater than or equal to E at the given temperature T. This exponential dependence of a reaction rate on temperature is known as the Arrhenius equation. The activation energy necessary for a chemical reaction can be in the form of heat, light, electricity or mechanical force in the form of ultrasound.^[42]

A related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. A reaction is feasible only if the total change in the Gibbs free energy is negative, $\Delta G \le 0 \,$ ; if it is equal to zero the chemical reaction is said to be at equilibrium.

There exist only limited possible states of energy for electrons, atoms and molecules. These are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. The atoms/molecules in a higher energy state are said to be excited. The molecules/atoms of substance in an excited energy state are often much more reactive; that is, more amenable to chemical reactions.

The phase of a substance is invariably determined by its energy and the energy of its surroundings. When the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water (H₂O); a liquid at room temperature because its molecules are bound by hydrogen bonds.^[43] Whereas hydrogen sulfide (H₂S) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole-dipole interactions.

The transfer of energy from one chemical substance to another depends on the size of energy quanta emitted from one substance. However, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer. Thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat is more easily transferred between substances relative to light or other forms of electronic energy. For example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy.

The existence of characteristic energy levels for different chemical substances is useful for their identification by the analysis of spectral lines. Different kinds of spectra are often used in chemical spectroscopy, e.g. IR, microwave, NMR, ESR, etc. Spectroscopy is also used to identify the composition of remote objects - like stars and distant galaxies - by analyzing their radiation spectra.

Emission spectrum of iron

The term chemical energy is often used to indicate the potential of a chemical substance to undergo a transformation through a chemical reaction or to transform other chemical substances.

Chemical laws

Main article: Chemical law

Chemical reactions are governed by certain laws, which have become fundamental concepts in chemistry. Some of them are:

Avogadro's law
Beer-Lambert law
Boyle's law (1662, relating pressure and volume)
Charles's law (1787, relating volume and temperature)
Fick's law of diffusion
Gay-Lussac's law (1809, relating pressure and temperature)
Henry's law
Hess's Law
Law of conservation of energy leads to the important concepts of equilibrium, thermodynamics, and kinetics.
Law of conservation of mass, according to the modern physics it is actually energy that is conserved, and that energy and mass are related; a concept which becomes important in nuclear chemistry.
Law of definite composition, although in many systems (notably biomacromolecules and minerals) the ratios tend to require large numbers, and are frequently represented as a fraction.
Law of multiple proportions
Raoult's Law

Subdisciplines

Chemistry is typically divided into several major sub-disciplines. There are also several main cross-disciplinary and more specialized fields of chemistry.^[44]

Analytical chemistry is the analysis of material samples to gain an understanding of their chemical composition and structure. Analytical chemistry incorporates standardized experimental methods in chemistry. These methods may be used in all subdisciplines of chemistry, excluding purely theoretical chemistry.
Biochemistry is the study of the chemicals, chemical reactions and chemical interactions that take place in living organisms. Biochemistry and organic chemistry are closely related, as in medicinal chemistry or neurochemistry. Biochemistry is also associated with molecular biology and genetics.
Inorganic chemistry is the study of the properties and reactions of inorganic compounds. The distinction between organic and inorganic disciplines is not absolute and there is much overlap, most importantly in the sub-discipline of organometallic chemistry.
Materials chemistry is the preparation, characterization, and understanding of substances with a useful function. The field is a new breadth of study in graduate programs, and it integrates elements from all classical areas of chemistry with a focus on fundamental issues that are unique to materials. Primary systems of study include the chemistry of condensed phases (solids, liquids, polymers) and interfaces between different phases.
Neurochemistry is the study of neurochemicals; including transmitters, peptides, proteins, lipids, sugars, and nucleic acids; their interactions, and the roles they play in forming, maintaining, and modifying the nervous system.
Nuclear chemistry is the study of how subatomic particles come together and make nuclei. Modern Transmutation is a large component of nuclear chemistry, and the table of nuclides is an important result and tool for this field.
Organic chemistry is the study of the structure, properties, composition, mechanisms, and reactions of organic compounds. An organic compound is defined as any compound based on a carbon skeleton.
Physical chemistry is the study of the physical and fundamental basis of chemical systems and processes. In particular, the energetics and dynamics of such systems and processes are of interest to physical chemists. Important areas of study include chemical thermodynamics, chemical kinetics, electrochemistry, statistical mechanics, and spectroscopy. Physical chemistry has large overlap with molecular physics. Physical chemistry involves the use of infinitesimal calculus in deriving equations. It is usually associated with quantum chemistry and theoretical chemistry. Physical chemistry is a distinct discipline from chemical physics.
Theoretical chemistry is the study of chemistry via fundamental theoretical reasoning (usually within mathematics or physics). In particular the application of quantum mechanics to chemistry is called quantum chemistry. Since the end of the Second World War, the development of computers has allowed a systematic development of computational chemistry, which is the art of developing and applying computer programs for solving chemical problems. Theoretical chemistry has large overlap with (theoretical and experimental) condensed matter physics and molecular physics.

Other fields include agrochemistry, astrochemistry, atmospheric chemistry, chemical engineering, chemical biology, chemo-informatics, electrochemistry, environmental chemistry, femtochemistry, flavor chemistry, flow chemistry, geochemistry, green chemistry, histochemistry, history of chemistry, hydrogenation chemistry, immunochemistry, marine chemistry, materials science, mathematical chemistry, mechanochemistry, medicinal chemistry, molecular biology, molecular mechanics, nanotechnology, natural product chemistry, oenology, neurochemistry, organometallic chemistry, petrochemistry, pharmacology, photochemistry, physical organic chemistry, phytochemistry, polymer chemistry, radiochemistry, solid-state chemistry, sonochemistry, supramolecular chemistry, surface chemistry, synthetic chemistry, thermochemistry, and many others.

Chemical industry

Main article: Chemical industry

The chemical industry represents an important economic activity. The global top 50 chemical producers in 2004 had sales of 587 billion US dollars with a profit margin of 8.1% and research and development spending of 2.1% of total chemical sales.^[45]

Professional societies

References

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^ What is Chemistry?
^ Matter: Atoms from Democritus to Dalton by Anthony Carpi, Ph.D.
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^ IUPAC Gold Book Definition
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"Chemistry as a science was almost created by the Muslims; for in this field, where the Greeks (so far as we know) were confined to industrial experience and vague hypothesis, the Saracens introduced precise observation, controlled experiment, and careful records. They invented and named the alembic (al-anbiq), chemically analyzed innumerable substances, composed lapidaries, distinguished alkalis and acids, investigated their affinities, studied and manufactured hundreds of drugs. Alchemy, which the Muslims inherited from Egypt, contributed to chemistry by a thousand incidental discoveries, and by its method, which was the most scientific of all medieval operations."
^ Dr. K. Ajram (1992), Miracle of Islamic Science, Appendix B, Knowledge House Publishers, ISBN 0911119434.

"Humboldt regards the Muslims as the founders of chemistry."
^ Will Durant (1935): Our Oriental Heritage: Simon & Schuster:

"Something has been said about the chemical excellence of cast iron in ancient India, and about the high industrial development of the Gupta times, when India was looked to, even by Imperial Rome, as the most skilled of the nations in such chemical industries as dyeing, tanning, soap-making, glass and cement... By the sixth century the Hindus were far ahead of Europe in industrial chemistry; they were masters of calcination, distillation, sublimation, steaming, fixation, the production of light without heat, the mixing of anesthetic and soporific powders, and the preparation of metallic salts, compounds and alloys. The tempering of steel was brought in ancient India to a perfection unknown in Europe till our own times; King Porus is said to have selected, as a specially valuable gift from Alexander, not gold or silver, but thirty pounds of steel. The Moslems took much of this Hindu chemical science and industry to the Near East and Europe; the secret of manufacturing "Damascus" blades, for example, was taken by the Arabs from the Persians, and by the Persians from India.""
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^ IUPAC Provisional Recommendations for the Nomenclature of Inorganic Chemistry (2004) [6]
^ Official SI Unit definitions
^ http://www.apsidium.com/theory/lewis_acid.htm Lewis concept of acids
^ http://www.bbc.co.uk/dna/h2g2/A708257 History of Acidity
^ visionlearning: Chemical Bonding by Anthony Carpi, Ph. [7]
^ Chemical Reaction Equation- IUPAC Goldbook
^ Gold Book Chemical Reaction IUPAC Goldbook
^ Reilly, Michael. (2007). Mechanical force induces chemical reaction, NewScientist.com news service, Reilly
^ Changing States of Matter - Chemforkids.com
^ The Canadian Encyclopedia: Chemistry Subdisciplines [8]
^ "Top 50 Chemical Producers". Chemical & Engineering News 83 (29): 20–23. July 18, 2005. http://pubs.acs.org/cen/coverstory/83/8329globaltop50.html.

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Misspellings: chemistry

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Common misspelling(s) of chemistry

chemestry

Translations: Chemistry

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Dansk (Danish)
n. - kemi

Nederlands (Dutch)
scheikunde, chemische samenstelling, complex proces, aantrekking of interactie tussen mensen

Français (French)
n. - chimie, propriétés chimiques, (fig) affinités

Deutsch (German)
n. - Chemie

Ελληνική (Greek)
n. - χημεία

Italiano (Italian)
chimica

Português (Portuguese)
n. - química (f)

Русский (Russian)
химия

Español (Spanish)
n. - química

Svenska (Swedish)
n. - kemi

中文（简体）(Chinese (Simplified))
化学, 化学作用

中文（繁體）(Chinese (Traditional))
n. - 化學, 化學作用

한국어 (Korean)
n. - 화학, 화학작용, 마음이 통함

日本語 (Japanese)
n. - 化学, 化学的性質, 化学現象

العربيه (Arabic)
‏(الاسم) كيمياء, علم الكيمياء‏

עברית (Hebrew)
n. - ‮כימיה‬

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		Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved. Read more
		US History Encyclopedia. © 2006 through a partnership of Answers Corporation. All rights reserved. Read more
		Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/. Read more
		History 1450-1789. Encyclopedia of the Early Modern World. Copyright © 2004 by The Gale Group, Inc. All rights reserved. Read more
		Quotes About. Copyright © 2005 QuotationsBook.com. All rights reserved. Read more
		Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Chemistry". Read more
		Misspellings. © 1999-2009 by Answers Corporation. All rights reserved. Read more
		Translations. Copyright © 2007, WizCom Technologies Ltd. All rights reserved. Read more

chemistry

Contents

Summary

History

Etymology

Definitions

Basic concepts

Atom

Element

Compound

Substance

Molecule

Mole

Ions and salts

Acidity and basicity

Phase

Redox

Chemical bond

Chemical reaction

Energy

Chemical laws

Subdisciplines

Chemical industry

Professional societies

See also

References

Further reading

Popular reading

Introductory undergraduate text books

Advanced undergraduate-level or graduate text books

External links

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