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Thehistory of chemistry represents a time span fromancient history to the present. By 1000 BC, civilizations used technologies that would eventually form the basis of the various branches of chemistry. Examples include the discovery of fire, extractingmetals fromores, makingpottery and glazes, fermentingbeer andwine, extracting chemicals from plants formedicine andperfume, rendering fat intosoap, makingglass,and makingalloys likebronze.
Theprotoscience of chemistry, andalchemy, was unsuccessful in explaining the nature of matter and its transformations. However, by performing experiments and recording the results, alchemists set the stage formodern chemistry.
The history of chemistry is intertwined with thehistory of thermodynamics, especially through the work ofWillard Gibbs.[1]
Arguably the first chemical reaction used in a controlled manner wasfire. However, for millennia fire was seen simply as a mystical force that could transform one substance into another (burning wood, or boiling water) while producing heat and light. Fire affected many aspects of early societies. These ranged from the simplest facets of everyday life, such as cooking and habitat heating and lighting, to more advanced uses, such as making pottery and bricks and melting of metals to make tools. It was fire that led to the discovery ofglass and thepurification of metals; this was followed by the rise ofmetallurgy.[2]
A 100,000-year-oldochre-processing workshop was found atBlombos Cave inSouth Africa. It indicates that early humans had an elementary knowledge of mineral processing. Paintings drawn by early humans consisting of early humans mixing animal blood with other liquids found on cave walls also indicate a small knowledge of chemistry.[3][4]
The earliest recorded metal employed by humans seems to begold, which can be found free or "native". Small amounts of natural gold have been found in Spanish caves used during the latePaleolithic period, around 40,000 BC.[5] The earliest gold metallurgy is known from theVarna culture in Bulgaria, dating from c. 4600 BC.[6]
Silver,copper,tin andmeteoric iron can also be found native, allowing a limited amount ofmetalworking in ancient cultures.[7] Egyptian weapons made from meteoric iron in about 3000 BC were highly prized as "daggers from Heaven".[8]
During the early stages of metallurgy, methods of purification of metals were sought, and gold, known inancient Egypt as early as 2900 BC, became a precious metal.
Certain metals can be recovered from their ores by simply heating the rocks in a fire: notablytin,lead and (at a higher temperature) copper. This process is known assmelting. The first evidence of this extractive metallurgy dates from the 6th and 5th millennia BC, and was found in the archaeological sites of theVinča culture,Majdanpek,Jarmovac andPločnik inSerbia.[9] The earliest copper smelting is found at the Belovode site;[10] these examples include a copper axe from 5500 BC.[11] Other signs of early metals are found from the third millennium BC in places likePalmela (Portugal),Los Millares (Spain), andStonehenge (United Kingdom). However, as often happens in the study ofprehistoric times, the ultimate beginnings cannot be clearly defined and new discoveries are ongoing.
These first metals were single elements, or else combinations as naturally occurred. By combining copper and tin, a superior metal could be made, analloy calledbronze. This was a major technological shift that began theBronze Age about 3500 BC. The Bronze Age was a period in human cultural development when the most advanced metalworking (at least in systematic and widespread use) included techniques for smeltingcopper andtin from naturally occurring outcroppings of copper ores, and then smelting those ores to cast bronze. These naturally occurring ores typically included arsenic as a common impurity. Copper/tin ores are rare, as reflected in the absence of tin bronzes inwestern Asia before 3000 BC.
After the Bronze Age, the history of metallurgy was marked by armies seeking better weaponry. States inEurasia prospered when they made the superior alloys, which, in turn, made better armor and better weapons.[citation needed]
The Chinese are credited with the first ever use ofChromium to prevent rusting. Modern archaeologists discovered that bronze-tippedcrossbow bolts at thetomb of Qin Shi Huang showed no sign of corrosion after more than 2,000 years, because they had been coated in chromium.[12][13] Chromium was not used anywhere else until the experiments of French pharmacist and chemistLouis Nicolas Vauquelin (1763–1829) in the late 1790s.[14]In multiple Warring States period tombs, sharp swords and other weapons were also found to be coated with 10 to 15 micrometers ofchromium oxide, which left them in pristine condition to this day.[15]
Significant progress in metallurgy and alchemy was also made inancient India.[16]
The extraction ofiron from its ore into a workable metal is much more difficult than copper or tin. While iron is not better suited for tools than bronze (untilsteel was discovered), iron ore is much more abundant and common than either copper or tin, and therefore more often available locally, with no need to trade for it.
Iron working appears to have been invented by theHittites in about 1200 BC, beginning theIron Age. The secret of extracting and working iron was a key factor in the success of thePhilistines.[8][17]
Cast iron smithing as well as the innovation of theBlast Furnace andCupola furnace was invented in ancient China, during theWarring States period when armies sought to develop better weaponry and armor in state-armories. Many other applications, practices, and devices associated with or involved in metallurgy were also established in ancient China, with the innovations ofhydraulic-poweredtrip hammers, and double-acting pistonbellows.[18][19]
The Iron Age is named after the advent of iron working (ferrous metallurgy). Historical developments in ferrous metallurgy can be found in a wide variety of past cultures and civilizations. These include the ancient and medieval kingdoms and empires of the Middle East and Near East,ancient Iran,ancient Egypt, ancientNubia, andAnatolia (Turkey),Ancient Nok,Carthage, theGreeks andRomans of ancient Europe, medieval Europe, ancient and medieval China, ancient and medieval India, ancient and medieval Japan, amongst others.
Philosophical attempts to rationalize why different substances have different properties (color, density, smell), exist in different states (gaseous, liquid, and solid), and react in a different manner when exposed to environments, for example to water or fire or temperature changes, led ancient philosophers to postulate the first theories on nature and chemistry. The history of such philosophical theories that relate to chemistry can probably be traced back to every single ancient civilization. The common aspect in all these theories was the attempt to identify a small number of primaryclassical elements that make up all the various substances in nature. Substances like air, water, and soil/earth, energy forms, such as fire and light, and more abstract concepts such as thoughts,aether, and heaven, were common in ancient civilizations even in the absence of any cross-fertilization: for example ancient Greek, Indian, Mayan, and Chinese philosophies all consideredair,water,earth andfire as primary elements.[citation needed]
Around 420 BC,Empedocles stated that all matter is made up offour elemental substances: earth, fire, air and water. The early theory ofatomism can be traced back toancient Greece. Greek atomism was made popular by the Greek philosopherDemocritus, who declared that matter is composed of indivisible and indestructible particles called "atomos" around 380 BC. Earlier,Leucippus also declared that atoms were the most indivisible part of matter. This coincided with a similar declaration by theIndian philosopherKanada in hisVaisheshikasutras around the same time period.[20]Aristotle opposed the existence of atoms in 330 BC. A Greek text attributed toPolybus the physician (ca. 380 BC) argued that the human body is composed of fourhumours instead.Epicurus (fl. 300 BC) postulated a universe of indestructible atoms in which man himself is responsible for achieving a balanced life.
With the goal of explainingEpicurean philosophy to a Roman audience, theRoman poet and philosopherLucretius[21] wroteDe rerum natura (On the Nature of Things)[22] in the middle of the first century BC. In the work, Lucretius presents the principles ofatomism; the nature of themind andsoul; explanations ofsensation and thought; the development of the world and its phenomena; and explains a variety ofcelestial andterrestrial phenomena.
The earliest alchemists in the Western tradition seemed to have come fromGreco-Roman Egypt in the first centuries AD. In addition to technical work, many of them invented chemical apparatuses. Thebain-marie, or water bath, is named forMary the Jewess. Her work also gives the first descriptions of thetribikos andkerotakis.[23]Cleopatra the Alchemist described furnaces and has been credited with the invention of thealembic.[24] Later,Zosimos of Panopolis wrote books on alchemy, which he calledcheirokmeta, the Greek word for "things made by hand." These works include many references to recipes and procedures, as well as descriptions of instruments. Much of the early development of purification methods were described earlier byPliny the Elder in hisNaturalis Historia. He tried to explain those methods, as well as making acute observations of the state of many minerals.
The elemental system used in medievalalchemy was developed primarily byJābir ibn Hayyān and was rooted in the classical elements of Greek tradition.[25] His system consisted of the four Aristotelian elements of air, earth, fire, and water in addition to two philosophical elements:sulphur, characterizing the principle of combustibility, "the stone which burns"; andmercury, characterizing the principle of metallic properties. They were seen by early alchemists as idealized expressions of irreducible components of theuniverse[26] and are of larger consideration[clarification needed] within philosophical alchemy.
The three metallic principles (sulphur to flammability or combustion, mercury to volatility and stability, andsalt to solidity) became thetria prima of the Swiss alchemistParacelsus. He reasoned that Aristotle's four-element theory appeared in bodies as three principles. Paracelsus saw these principles as fundamental and justified them by recourse to the description of how wood burns in fire. Mercury included the cohesive principle, so that when it left the wood (in smoke) the wood fell apart. Smoke described the volatility (the mercurial principle), the heat-giving flames described flammability (sulphur), and the remnant ash described solidity (salt).[27]
Alchemy is defined by theHermetic quest for thephilosopher's stone, the study of which is steeped in symbolic mysticism, and differs greatly from modern science. Alchemists toiled to make transformations on anesoteric (spiritual) and/orexoteric (practical) level.[28] It was theprotoscientific, exoteric aspects of alchemy that contributed heavily to the evolution of chemistry inGreco-Roman Egypt, in theIslamic Golden Age, and then in Europe. Alchemy and chemistry share an interest in the composition and properties of matter, and until the 18th century they were not separate disciplines. The termchymistry has been used to describe the blend of alchemy and chemistry that existed before that time.[29]
During the Renaissance, exoteric alchemy remained popular in the form ofParacelsianiatrochemistry, while spiritual alchemy flourished, realigned to itsPlatonic, Hermetic, andGnostic roots. Consequently, the symbolic quest for the philosopher's stone was not superseded by scientific advances, and was still the domain of respected scientists and doctors until the early 18th century. Early modern alchemists who are renowned for their scientific contributions includeJan Baptist van Helmont,Robert Boyle, andIsaac Newton.
In theIslamic World, theMuslims were translating the works of ancientGreek andHellenistic philosophers into Arabic and were experimenting with scientific ideas.[30] The Arabic works attributed to the 8th-century alchemistJābir ibn Hayyān introduced a systematic classification of chemical substances, and provided instructions for deriving an inorganic compound (sal ammoniac orammonium chloride) fromorganic substances (such as plants, blood, and hair) by chemical means.[31] Some Arabic Jabirian works (e.g., the "Book of Mercy", and the "Book of Seventy") were later translated into Latin under theLatinized name "Geber",[32] and in 13th-century Europe an anonymous writer, usually referred to aspseudo-Geber, started to produce alchemical and metallurgical writings under this name.[33] Influential scholars, such asAbū al-Rayhān al-Bīrūnī[34] andAvicenna[35] disputed the theories of alchemy, particularly the theory of thetransmutation of metals.
There were several problems with alchemy, as seen from today's standpoint. There was no systematic naming scheme for new compounds, and the language was esoteric and vague to the point that the terminologies meant different things to different people. In fact, according toThe Fontana History of Chemistry (Brock, 1992):
The language of alchemy soon developed an arcane and secretive technical vocabulary designed to conceal information from the uninitiated. To a large degree, this language is incomprehensible to us today, though it is apparent that readers ofGeoffrey Chaucer'sCanon's Yeoman's Tale or audiences ofBen Jonson'sThe Alchemist were able to construe it sufficiently to laugh at it.[36]
Chaucer's tale exposed the more fraudulent side of alchemy, especially the manufacture of counterfeit gold from cheap substances. Less than a century earlier,Dante Alighieri also demonstrated an awareness of this fraudulence, causing him to consign all alchemists to theInferno in his writings. Soon afterwards, in 1317, theAvignonPope John XXII ordered all alchemists to leave France for making counterfeit money. A law was passed in England in 1403 which made the "multiplication of metals" punishable by death. Despite these and other apparently extreme measures, alchemy did not die. Royalty and privileged classes still sought to discover the philosopher's stone and the elixir of life for themselves.[37]
There was also no agreed-upon scientific method for making experiments reproducible. Indeed, many alchemists included in their methods irrelevant information such as the timing of the tides or the phases of the moon. The esoteric nature and codified vocabulary of alchemy appeared to be more useful in concealing the fact that they could not be sure of very much at all. As early as the 14th century, cracks seemed to grow in the facade of alchemy; and people became sceptical.[citation needed] Clearly, there needed to be a scientific method in which experiments could be repeated by other people, and results needed to be reported in a clear language that laid out both what was known and what was unknown.
Practical attempts to improve the refining of ores and their extraction to smelt metals was an important source of information for early chemists in the 16th century, among themGeorg Agricola (1494–1555), who published his great workDe re metallica in 1556. His work describes the highly developed and complex processes of mining metal ores, metal extraction and metallurgy of the time. His approach removed the mysticism associated with the subject, creating the practical base upon which others could build. The work describes the many kinds of furnace used to smelt ore, and stimulated interest in minerals and their composition. It is no coincidence that he gives numerous references to the earlier author, Pliny the Elder and hisNaturalis Historia. Agricola has been described as the "father of metallurgy" and the founder ofgeology as a scientific discipline.[39][40][41]
In 1605,Sir Francis Bacon publishedThe Proficience and Advancement of Learning, which contains a description of what would later be known as thescientific method.[42] In 1605,Michal Sedziwój publishes the alchemical treatiseA New Light of Alchemy which proposed the existence of the "food of life" within air, much later recognized as oxygen. In 1615Jean Beguin published theTyrocinium Chymicum, an early chemistry textbook, and in it draws the first-everchemical equation.[43] In 1637René Descartes publishesDiscours de la méthode, which contains an outline of the scientific method.
The Dutch chemistJan Baptist van Helmont's workOrtus medicinae was published posthumously in 1648; the book is cited by some as a major transitional work between alchemy and chemistry, and as an important influence onRobert Boyle. The book contains the results of numerous experiments and establishes an early version of thelaw of conservation of mass. Working during the time just afterParacelsus andiatrochemistry, Jan Baptist van Helmont suggested that there are insubstantial substances other than air and coined a name for them – "gas", from the Greek wordchaos. In addition to introducing the word "gas" into the vocabulary of scientists, van Helmont conducted several experiments involving gases. Jan Baptist van Helmont is also remembered today largely for his ideas onspontaneous generation and his 5-yeartree experiment, as well as being considered the founder ofpneumatic chemistry.
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Anglo-Irish chemistRobert Boyle (1627–1691) is considered to have initiated the gradual separation of chemistry from alchemy.[44] Although skeptical of elements and convinced of alchemy, Boyle played a key part in elevating the "sacred art" as an independent, fundamental and philosophical discipline. He is best known forBoyle's law, which he presented in 1662, though he was not the first to discover it.[45] The law describes the inversely proportional relationship between the absolutepressure andvolume of a gas, if the temperature is kept constant within aclosed system.[46][47]
Boyle is also credited for his landmark publicationThe Sceptical Chymist (1661), which advocated for a rigorous approach to experimentation among chemists. In the work, Boyle questioned some commonly held alchemical theories and argued for practitioners to be more "philosophical" and less commercially focused.[48] He rejected the classical four elements of earth, fire, air, and water, and proposed a mechanistic alternative of atoms andchemical reactions that could be subject to rigorous experiment.
Boyle also tried to purify chemicals to obtain reproducible reactions. He was a vocal proponent of the mechanical philosophy proposed byRené Descartes to explain and quantify the physical properties and interactions of material substances. Boyle was an atomist, but favoured the wordcorpuscle overatoms. He commented that the finest division of matter where the properties are retained is at the level of corpuscles.
Boyle repeated the tree experiment of van Helmont, and was the first to useindicators which changed colors with acidity. He also performed numerous investigations with anair pump, and noted that themercury fell as air was pumped out. He also observed that pumping the air out of a container would extinguish a flame and kill small animals placed inside. Through his works, Boyle helped to lay the foundations for thechemical revolution two centuries later.[49]
In 1702, German chemistGeorg Stahl coined the name "phlogiston" for the substance believed to be released in the process of burning. Around 1735, Swedish chemistGeorg Brandt analyzed a dark blue pigment found in copper ore. Brandt demonstrated that the pigment contained a new element, later namedcobalt. In 1751, a Swedish chemist and pupil of Stahl's namedAxel Fredrik Cronstedt, identified an impurity in copper ore as a separate metallic element, which he namednickel. Cronstedt is one of the founders of modernmineralogy.[50] Cronstedt also discovered the mineralscheelite in 1751, which he named tungsten, meaning "heavy stone" in Swedish.
In 1754, Scottish chemistJoseph Black isolatedcarbon dioxide, which he called "fixed air".[51] In 1757,Louis Claude Cadet de Gassicourt, while investigating arsenic compounds, createsCadet's fuming liquid, later discovered to becacodyl oxide, considered to be the first syntheticorganometallic compound.[52] In 1758, Joseph Black formulated the concept oflatent heat to explain thethermochemistry ofphase changes.[53] In 1766, English chemistHenry Cavendish isolatedhydrogen, which he called "inflammable air". Cavendish discovered hydrogen as a colorless, odourless gas that burns and can form an explosive mixture with air, and published a paper on the production of water by burning inflammable air (that is, hydrogen) in dephlogisticated air (now known to be oxygen), the latter a constituent of atmospheric air (phlogiston theory).
In 1773,Swedish German[54] chemistCarl Wilhelm Scheele discoveredoxygen, which he called "fire air", but did not immediately publish his achievement.[55] In 1774, English chemistJoseph Priestley independently isolated oxygen in its gaseous state, calling it "dephlogisticated air", and published his work before Scheele.[56][57] During his lifetime, Priestley's considerable scientific reputation rested on his invention ofsoda water, his writings onelectricity, and his discovery of several "airs" (gases), the most famous being what Priestley dubbed "dephlogisticated air" (oxygen). However, Priestley's determination to defend phlogiston theory and to reject what would become thechemical revolution eventually left him isolated within the scientific community.
In 1781, Carl Wilhelm Scheele discovered that a newacid,tungstic acid, could be made from Cronstedt's scheelite (at the time named tungsten). Scheele andTorbern Bergman suggested that it might be possible to obtain a new metal by reducing this acid.[58] In 1783,José andFausto Elhuyar found an acid made fromwolframite that was identical to tungstic acid. Later that year, in Spain, the brothers succeeded in isolating the metal now known astungsten by reduction of this acid withcharcoal, and they are credited with the discovery of the element.[59][60]
Italian physicistAlessandro Volta constructed a device for accumulating a large charge by a series of inductions and groundings. He investigated the 1780s discovery "animal electricity" byLuigi Galvani, and found that theelectric current was generated from the contact of dissimilar metals, and that the frog leg was only acting as a detector. Volta demonstrated in 1794 that when two metals and brine-soaked cloth or cardboard are arranged in a circuit they produce anelectric current.
In 1800, Volta stacked several pairs of alternatingcopper (orsilver) andzinc discs (electrodes) separated by cloth or cardboard soaked inbrine (electrolyte) to increase the electrolyte conductivity.[61] When the top and bottom contacts were connected by a wire, an electriccurrent flowed through thisvoltaic pile and the connecting wire. Thus, Volta is credited with constructing the firstelectrical battery to produceelectricity.
Thus, Volta is considered to be the founder of the discipline ofelectrochemistry.[62] AGalvanic cell (or voltaic cell) is anelectrochemical cell that derives electrical energy from a spontaneousredox reaction taking place within the cell. It generally consists of two different metals connected by asalt bridge, or individual half-cells separated by a porous membrane.
Antoine-Laurent de Lavoisier demonstrated with careful measurements that transmutation of water to earth was not possible, but that the sediment observed from boiling water came from the container. He burnt phosphorus and sulfur in air, and proved that the products weighed more than the original samples, with the mass gained being lost from the air. Thus, in 1789, he established the Law ofConservation of Mass, which is also called "Lavoisier's Law."[63]
Repeating the experiments of Priestley, he demonstrated that air is composed of two parts, one of which combines with metals to formcalxes. InConsidérations Générales sur la Nature des Acides (1778), he demonstrated that the "air" responsible for combustion was also the source of acidity. The next year, he named this portion oxygen (Greek for acid-former), and the other azote (Greek for no life). Because of his more thorough characterization of it as an element, Lavoisier thus has a claim to the discovery of oxygen along with Priestley and Scheele. He also discovered that the "inflammable air" discovered by Cavendish – which he termedhydrogen (Greek for water-former) – combined with oxygen to produce a dew, as Priestley had reported, which appeared to be water. InReflexions sur le Phlogistique (1783), Lavoisier showed thephlogiston theory of combustion to be inconsistent.Mikhail Lomonosov independently established a tradition of chemistry in Russia in the 18th century; he also rejected the phlogiston theory, and anticipated thekinetic theory of gases. Lomonosov regarded heat as a form of motion, and stated the idea of conservation of matter.
Lavoisier worked withClaude Louis Berthollet and others to devise a system ofchemical nomenclature, which serves as the basis of the modern system of naming chemical compounds. In hisMethods of Chemical Nomenclature (1787), Lavoisier invented the system of naming and classification still largely in use today, including names such assulfuric acid,sulfates, andsulfites. In 1785, Berthollet was the first to introduce the use of chlorine gas as a commercial bleach. In the same year he first determined the elemental composition of the gasammonia. Berthollet first produced a modern bleaching liquid in 1789 by passing chlorine gas through a solution ofsodium carbonate – the result was a weak solution ofsodium hypochlorite. Another strong chlorine oxidant and bleach which he investigated and was the first to produce,potassium chlorate (KClO3), is known as Berthollet's Salt. Berthollet is also known for his scientific contributions to the theory ofchemical equilibrium via the mechanism ofreversible reactions.
Lavoisier'sTraité Élémentaire de Chimie (Elementary Treatise of Chemistry, 1789) was the first modern chemical textbook, and presented a unified view of new theories of chemistry, contained a clear statement of the Law of Conservation of Mass, and denied the existence of phlogiston. In addition, it contained a list of elements, or substances that could not be broken down further, which included oxygen,nitrogen, hydrogen,phosphorus,mercury,zinc, andsulfur. His list, however, also included light andcaloric, which he believed to be material substances. In the work, Lavoisier underscored the observational basis of his chemistry, stating "I have tried...to arrive at the truth by linking up facts; to suppress as much as possible the use of reasoning, which is often an unreliable instrument which deceives us, in order to follow as much as possible the torch of observation and of experiment." Nevertheless, he believed that the real existence of atoms was philosophically impossible. Lavoisier demonstrated that organisms disassemble and reconstitute atmospheric air in the same manner as a burning body.
WithPierre-Simon Laplace, Lavoisier used acalorimeter to estimate the heat evolved per unit of carbon dioxide produced. They found the same ratio for a flame and animals, indicating that animals produced energy by a type of combustion. Lavoisier believed in theradical theory, which stated that radicals, which function as a single group in a chemical reaction, would combine with oxygen in reactions. He believed all acids contained oxygen. He also discovered thatdiamond is a crystalline form of carbon.
Although many of Lavoisier's partners were influential for the advancement of chemistry as a scientific discipline, his wife Marie-Anne Lavoisier was arguably the most influential of them all. Upon their marriage, Mme. Lavoisier began to study chemistry, English, and drawing in order to help her husband in his work either by translating papers into English, a language which Lavoisier did not know, or by keeping records and drawing the various apparatuses that Lavoisier used in his labs.[64] Through her ability to read and translate articles from Britain for her husband, Lavoisier had access to knowledge of many of the chemical advances happening outside of his lab. Furthermore, Mme. Lavoisier kept records of her husband's work and ensured that his works were published. The first sign of Marie-Anne's true potential as a chemist in Lavoisier's lab came when she was translating a book by the scientistRichard Kirwan. While translating, she stumbled upon and corrected multiple errors. When she presented her translation, along with her notes, to Lavoisier, her contributions led to Lavoisier's refutation of the theory of phlogiston.
Lavoisier made many fundamental contributions to the science of chemistry. Following his work, chemistry acquired a strict, quantitative nature, allowing reliable predictions to be made. Therevolution in chemistry which he brought about was a result of a conscious effort to fit all experiments into the framework of a single theory. He established the consistent use of chemical balance, used oxygen to overthrow the phlogiston theory, and developed a new system of chemical nomenclature. Further potential contributions were cut short when Lavoisier was beheaded during theFrench Revolution.
Throughout the 19th century, chemistry was divided between those who followed the atomic theory ofJohn Dalton and theenergeticists, such asWilhelm Ostwald andErnst Mach.[65] Although such proponents of the atomic theory asAmedeo Avogadro andLudwig Boltzmann made great advances in explaining the behavior ofgases, this dispute was not finally settled untilJean Perrin's experimental investigation ofEinstein's atomic explanation ofBrownian motion in the first decade of the 20th century.[65]
Well before the dispute had been settled, many had already applied the concept of atomism to chemistry. A major example was theion theory ofSvante Arrhenius which anticipated ideas about atomic substructure that did not fully develop until the 20th century.Michael Faraday was another early worker, whose major contribution to chemistry waselectrochemistry, in which (among other things) a certain quantity of electricity duringelectrolysis orelectrodeposition of metals was shown to be associated with certain quantities of chemical elements, and fixed quantities of the elements therefore with each other, in specific ratios.[citation needed] These findings, like those of Dalton's combining ratios, were early clues to the atomic nature of matter.
In 1803, English meteorologist and chemistJohn Dalton proposedDalton's law, which describes the relationship between the components in a mixture of gases and the relative pressure each contributes to that of the overall mixture.[66] Discovered in 1801, this concept is also known as Dalton's law of partial pressures.
Dalton also proposed a modernatomic theory in 1803 which stated that all matter was composed of small indivisible particles termed atoms, atoms of a given element possess unique characteristics and weight, and three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules). In 1808, Dalton first publishedNew System of Chemical Philosophy (1808–1827), in which he outlined the first modern scientific description of the atomic theory. This work identified chemical elements as a specific type of atom, therefore rejectingNewton's theory of chemical affinities.
Instead, Dalton inferred proportions of elements in compounds by taking ratios of the weights of reactants, setting the atomic weight of hydrogen to be identically one. FollowingJeremias Benjamin Richter (known for introducing the termstoichiometry), he proposed that chemical elements combine in integral ratios. This is known as thelaw of multiple proportions or Dalton's law, and Dalton included a clear description of the law in hisNew System of Chemical Philosophy. The law of multiple proportions is one of the basic laws of stoichiometry used to establish the atomic theory. Despite the importance of the work as the first view of atoms as physically real entities and the introduction of a system of chemical symbols,New System of Chemical Philosophy devoted almost as much space to the caloric theory as to atomism.
French chemistJoseph Proust proposed thelaw of definite proportions, which states that elements always combine in small, whole number ratios to form compounds, based on several experiments conducted between 1797 and 1804.[67] Along with the law of multiple proportions, the law of definite proportions forms the basis of stoichiometry. The law of definite proportions and constant composition do not prove that atoms exist, but they are difficult to explain without assuming that chemical compounds are formed when atoms combine in constant proportions.
A Swedish chemist and disciple of Dalton,Jöns Jacob Berzelius embarked on a systematic program to try to make accurate and precise quantitative measurements and to ensure the purity of chemicals. Along with Lavoisier, Boyle, and Dalton, Berzelius is known as the father of modern chemistry. In 1828 he compiled a table of relative atomic weights, whereoxygen was used as a standard, with its weight set at 100, and which included all of the elements known at the time. This work provided evidence in favor of Dalton's atomic theory – that inorganic chemical compounds are composed of atoms combined inwhole number amounts. He determined the exact elementary constituents of a large number of compounds; the results strongly supported Proust's Law of Definite Proportions. In discovering that atomic weights are not integer multiples of the weight of hydrogen, Berzelius also disprovedProut's hypothesis that elements are built up from atoms of hydrogen.
Motivated by his extensive atomic weight determinations and in a desire to aid his experiments, he introduced the classical system ofchemical symbols and notation with his 1808 publicationLärbok i Kemien, in which elements are abbreviated to one or two letters to make a distinct symbol from their Latin name. This system of chemical notation—in which the elements were given simple written labels, such as O for oxygen, or Fe for iron, with proportions denoted by numbers—is the same basic system used today. The only difference is that instead of the subscript number used today (e.g., H2O), Berzelius used a superscript (H2O). Berzelius is credited with identifying the chemical elementssilicon,selenium,thorium, andcerium. Students working in Berzelius's laboratory also discoveredlithium andvanadium.
Berzelius developed theradical theory of chemical combination, which holds that reactions occur as stable groups of atoms calledradicals are exchanged between molecules. He believed that salts are compounds formed ofacids andbases, and discovered that the anions in acids were attracted to a positive electrode (theanode), whereas the cations in a base were attracted to a negative electrode (thecathode). Berzelius did not believe in theVitalism Theory, but instead in a regulative force which produced organization of tissues in an organism. Berzelius is also credited with originating the chemical terms "catalysis", "polymer", "isomer", and "allotrope", although his original definitions differ dramatically from modern usage. For example, he coined the term "polymer" in 1833 to describe organic compounds which shared identical empirical formulas but which differed in overall molecular weight, the larger of the compounds being described as "polymers" of the smallest. By this long-superseded, pre-structural definition,glucose (C6H12O6) was viewed as a polymer offormaldehyde (CH2O).
English chemistHumphry Davy was a pioneer in the field ofelectrolysis, using Alessandro Volta's voltaic pile to split up common compounds and thus isolate a series of new elements. He went on to electrolyse molten salts and discovered several new metals, especiallysodium andpotassium, highly reactive elements known as thealkali metals. Potassium, the first metal that was isolated by electrolysis, was discovered in 1807 by Davy, who derived it fromcaustic potash (KOH). Before the 19th century, no distinction was made between potassium and sodium. Sodium was first isolated by Davy in the same year by passing an electric current through moltensodium hydroxide (NaOH). When Davy heard that Berzelius and Pontin prepared calcium amalgam by electrolyzing lime in mercury, he tried it himself. Davy was successful, and discoveredcalcium in 1808 by electrolyzing a mixture oflime andmercuric oxide.[68][69] He worked with electrolysis throughout his life and, in 1808, he isolatedmagnesium,strontium[70] andbarium.[71]
Davy also experimented with gases by inhaling them. This experimental procedure nearly proved fatal on several occasions, but led to the discovery of the unusual effects ofnitrous oxide, which came to be known as laughing gas.Chlorine was discovered in 1774 by Swedish chemistCarl Wilhelm Scheele, who called it"dephlogisticated marine acid" (seephlogiston theory) and mistakenly thought it containedoxygen. Scheele observed several properties of chlorine gas, such as its bleaching effect on litmus, its deadly effect on insects, its yellow-green colour, and the similarity of its smell to that ofaqua regia. However, Scheele was unable to publish his findings at the time. In 1810, chlorine was given its current name by Humphry Davy (derived from the Greek word for green), who insisted that chlorine was in fact anelement.[72] He also showed thatoxygen could not be obtained from the substance known asoxymuriatic acid (HCl solution). This discovery overturnedLavoisier's definition of acids as compounds of oxygen. Davy was a popular lecturer and able experimenter.
French chemistJoseph Louis Gay-Lussac shared the interest of Lavoisier and others in the quantitative study of the properties of gases. From his first major program of research in 1801–1802, he concluded that equal volumes of all gases expand equally with the same increase in temperature: this conclusion is usually called "Charles's law", as Gay-Lussac gave credit toJacques Charles, who had arrived at nearly the same conclusion in the 1780s but had not published it.[73] The law was independently discovered by British natural philosopher John Dalton by 1801, although Dalton's description was less thorough than Gay-Lussac's.[74][75] In 1804 Gay-Lussac made several daring ascents of over 7,000 meters above sea level in hydrogen-filled balloons—a feat not equaled for another 50 years—that allowed him to investigate other aspects of gases. Not only did he gather magnetic measurements at various altitudes, but he also took pressure, temperature, and humidity measurements and samples of air, which he later analyzed chemically.
In 1808 Gay-Lussac announced what was probably his single greatest achievement: from his own and others' experiments he deduced that gases at constant temperature and pressure combine in simple numerical proportions by volume, and the resulting product or products—if gases—also bear a simple proportion by volume to the volumes of the reactants. In other words, gases under equal conditions of temperature and pressure react with one another in volume ratios of small whole numbers. This conclusion subsequently became known as "Gay-Lussac's law" or the "Law of Combining Volumes". With his fellow professor at theÉcole Polytechnique,Louis Jacques Thénard, Gay-Lussac also participated in early electrochemical research, investigating the elements discovered by its means. Among other achievements, they decomposedboric acid by using fused potassium, thus discovering the elementboron. The two also took part in contemporary debates that modified Lavoisier's definition of acids and furthered his program of analyzing organic compounds for their oxygen and hydrogen content.
The elementiodine was discovered by French chemistBernard Courtois in 1811.[76][77] Courtois gave samples to his friends,Charles Bernard Desormes (1777–1862) andNicolas Clément (1779–1841), to continue research. He also gave some of the substance to Gay-Lussac and to physicistAndré-Marie Ampère. On December 6, 1813, Gay-Lussac announced that the new substance was either an element or a compound of oxygen.[78][79][80] It was Gay-Lussac who suggested the name"iode", from the Greek word ιώδες (iodes) for violet (because of the color of iodine vapor).[76][78] Ampère had given some of his sample to Humphry Davy. Davy did some experiments on the substance and noted its similarity to chlorine.[81] Davy sent a letter dated December 10 to theRoyal Society of London stating that he had identified a new element.[82] Arguments erupted between Davy and Gay-Lussac over who identified iodine first, but both scientists acknowledged Courtois as the first to isolate the element.
In 1815, Humphry Davy invented theDavy lamp, which allowed miners withincoal mines to work safely in the presence of flammable gases. There had been many mining explosions caused byfiredamp ormethane often ignited by open flames of the lamps then used by miners. Davy conceived of using an iron gauze to enclose a lamp's flame, and so prevent the methane burning inside the lamp from passing out to the general atmosphere. Although the idea of thesafety lamp had already been demonstrated byWilliam Reid Clanny and by the then unknown (but later very famous) engineerGeorge Stephenson, Davy's use of wire gauze to prevent the spread of flame was used by many other inventors in their later designs. There was some discussion as to whether Davy had discovered the principles behind his lamp without the help of the work ofSmithson Tennant, but it was generally agreed that the work of both men had been independent. Davy refused to patent the lamp, and its invention led to him being awarded theRumford medal in 1816.[83]
After Dalton published his atomic theory in 1808, certain of his central ideas were soon adopted by most chemists. However, uncertainty persisted for half a century about how atomic theory was to be configured and applied to concrete situations; chemists in different countries developed several different incompatible atomistic systems. A paper that suggested a way out of this difficult situation was published as early as 1811 by the Italian physicistAmedeo Avogadro (1776–1856), who hypothesized that equal volumes of gases at the sametemperature andpressure contain equal numbers of molecules, from which it followed that relativemolecular weights of any two gases are the same as the ratio of the densities of the two gases under the same conditions of temperature and pressure. Avogadro also reasoned that simple gases were not formed of solitary atoms but were instead compound molecules of two or more atoms. Thus Avogadro was able to overcome the difficulty that Dalton and others had encountered when Gay-Lussac reported that above 100 °C the volume of water vapor was twice the volume of the oxygen used to form it. According to Avogadro, the molecule of oxygen had split into two atoms in the course of forming water vapor.
Avogadro's hypothesis was neglected for half a century after it was first published. Many reasons for this neglect have been cited, including some theoretical problems, such as Jöns Jacob Berzelius's "dualism", which asserted that compounds are held together by the attraction of positive and negative electrical charges, making it inconceivable that a molecule composed of two electrically similar atoms—as in oxygen—could exist. An additional barrier to acceptance was the fact that many chemists were reluctant to adopt physical methods (such as vapour-density determinations) to solve their problems. By mid-century, however, some leading figures had begun to view the chaotic multiplicity of competing systems of atomic weights and molecular formulas as intolerable. Moreover, purely chemical evidence began to mount that suggested Avogadro's approach might be right after all. During the 1850s, younger chemists, such asAlexander Williamson in England,Charles Gerhardt andCharles-Adolphe Wurtz in France, andAugust Kekulé in Germany, began to advocate reforming theoretical chemistry to make it consistent with Avogadrian theory.
In 1825,Friedrich Wöhler andJustus von Liebig performed the first confirmed discovery and explanation ofisomers, earlier named by Berzelius. Working withcyanic acid andfulminic acid, they correctly deduced that isomerism was caused by differing arrangements of atoms within a molecular structure. In 1827,William Prout classified biomolecules into their modern groupings:carbohydrates,proteins andlipids. After the nature of combustion was settled, a dispute aboutvitalism and the essential distinction between organic and inorganic substances began. The vitalism question was revolutionized in 1828 when Friedrich Wöhler synthesizedurea, thereby establishing that organic compounds could be produced from inorganic starting materials and disproving the theory of vitalism.
This opened a new research field in chemistry, and by the end of the 19th century, scientists were able to synthesize hundreds of organic compounds. The most important among them aremauve,magenta, and other syntheticdyes, as well as the widely used drugaspirin. The discovery of the artificial synthesis of urea contributed greatly to the theory ofisomerism, as the empirical chemical formulas for urea andammonium cyanate are identical (seeWöhler synthesis). In 1832, Friedrich Wöhler and Justus von Liebig discovered and explainedfunctional groups andradicals in relation to organic chemistry, as well as first synthesizingbenzaldehyde. Liebig, a German chemist, made major contributions toagricultural andbiological chemistry, and worked on the organization oforganic chemistry, being considered one of its principal founders.[86] Liebig is also considered the "father of thefertilizer industry" for his discovery ofnitrogen as an essential plantnutrient, and his formulation of theLaw of the Minimum which described the effect of individual nutrients on crops.
Vladimir Markovnikov, born in 1838, was a Russian scientist who did most of his work at Kazan University in Russia.[87] At Kazan, he studied underButlerov in a laboratory better known as "the cradle of Russian organic chemistry", after which he also studied chemistry in Germany for two years.[87] Markovnikov's contributions to the fields of organic chemistry included the development of the eponymousMarkovnikov's rule, which states that hydrogen halides when added to alkenes and alkynes would add in a way that hydrogens would bond to the side of the carbon with the most hydrogen substituents.[88] Products in chemistry that follow this rule are considered Markovnikov products and those that did not are considered anti-Markovnikov products.[88] Markovnikov's rule was an early example ofregioselectivity in organic synthesis and the modern understanding of it continues to be important in the chemical industry, where catalysts have been developed to produce anti-Markovnikov products.[88] A significant aspect of Markovnikov's rule is that it explains reactivity based on the structural arrangement of atoms, as many chemists at the time did not consider chemical formulas as representing physical arrangement of atoms (see alsoradical theory).[89]
In 1840,Germain Hess proposedHess's law, an early statement of thelaw of conservation of energy, which establishes thatenergy changes in a chemical process depend only on the states of the starting and product materials and not on the specific pathway taken between the two states. In 1847,Hermann Kolbe obtainedacetic acid from completely inorganic sources, further disproving vitalism. In 1848,William Thomson, 1st Baron Kelvin (commonly known as Lord Kelvin) established the concept ofabsolute zero, the temperature at which all molecular motion ceases. In 1849,Louis Pasteur discovered that theracemic form oftartaric acid is a mixture of the levorotatory and dextrotatory forms, thus clarifying the nature ofoptical rotation and advancing the field ofstereochemistry.[90] In 1852,August Beer proposedBeer's law, which explains the relationship between the composition of a mixture and the amount of light it will absorb. Based partly on earlier work byPierre Bouguer andJohann Heinrich Lambert, it established theanalytical technique known asspectrophotometry.[91] In 1855,Benjamin Silliman, Jr. pioneered methods ofpetroleum cracking, which made the entire modernpetrochemical industry possible.[92]
Avogadro's hypothesis began to gain broad appeal among chemists only after his compatriot and fellow scientistStanislao Cannizzaro demonstrated its value in 1858, two years after Avogadro's death. Cannizzaro's chemical interests had originally centered on natural products and on reactions ofaromatic compounds; in 1853 he discovered that whenbenzaldehyde is treated with concentrated base, bothbenzoic acid andbenzyl alcohol are produced—a phenomenon known today as theCannizzaro reaction. In his 1858 pamphlet, Cannizzaro showed that a complete return to the ideas of Avogadro could be used to construct a consistent and robust theoretical structure that fit nearly all of the available empirical evidence. For instance, he pointed to evidence that suggested that not all elementary gases consist of two atoms per molecule—some weremonatomic, most werediatomic, and a few were even more complex.
Another point of contention had been the formulas for compounds of thealkali metals (such assodium) and thealkaline earth metals (such ascalcium), which, in view of their striking chemical analogies, most chemists had wanted to assign to the same formula type. Cannizzaro argued that placing these metals in different categories had the beneficial result of eliminating certain anomalies when using their physical properties to deduce atomic weights. Unfortunately, Cannizzaro's pamphlet was published initially only in Italian and had little immediate impact. The real breakthrough came with aninternational chemical congress held in the German town ofKarlsruhe in September 1860, at which most of the leading European chemists were present. The Karlsruhe Congress had been arranged by Kekulé, Wurtz, and a few others who shared Cannizzaro's sense of the direction chemistry should go. Speaking in French (as everyone there did), Cannizzaro's eloquence and logic made an indelible impression on the assembled body. Moreover, his friend Angelo Pavesi distributed Cannizzaro's pamphlet to attendees at the end of the meeting; more than one chemist later wrote of the decisive impression the reading of this document provided. For instance,Lothar Meyer later wrote that on reading Cannizzaro's paper, "The scales seemed to fall from my eyes."[93] Cannizzaro thus played a crucial role in winning the battle for reform. The system advocated by him, and soon thereafter adopted by most leading chemists, is substantially identical to what is still used today.
In 1856, SirWilliam Henry Perkin, age 18, given a challenge by his professor,August Wilhelm von Hofmann, sought to synthesizequinine, the anti-malaria drug, fromcoal tar. In one attempt, Perkinoxidized aniline usingpotassium dichromate, whosetoluidine impurities reacted with the aniline and yielded a black solid—suggesting a "failed" organic synthesis. Cleaning the flask with alcohol, Perkin noticed purple portions of the solution: a byproduct of the attempt was the first synthetic dye, known asmauveine or Perkin's mauve. Perkin's discovery is the foundation of the dye synthesis industry, one of the earliest successful chemical industries.
German chemistAugust Kekulé von Stradonitz's most important single contribution was his structural theory of organic composition, outlined in two articles published in 1857 and 1858 and treated in great detail in the pages of his extraordinarily popularLehrbuch der organischen Chemie ("Textbook of Organic Chemistry"), the first installment of which appeared in 1859 and gradually extended to four volumes. Kekulé argued that tetravalentcarbon atoms – that is, carbon forming exactly fourchemical bonds – could link together to form what he called a "carbon chain" or a "carbon skeleton," to which other atoms with other valences (such as hydrogen, oxygen, nitrogen, and chlorine) could join. He was convinced that it was possible for the chemist to specify this detailed molecular architecture for at least the simpler organic compounds known in his day. Kekulé was not the only chemist to make such claims in this era. The Scottish chemistArchibald Scott Couper published a substantially similar theory nearly simultaneously, and the Russian chemistAleksandr Butlerov did much to clarify and expand structure theory. However, it was predominantly Kekulé's ideas that prevailed in the chemical community.
British chemist and physicistWilliam Crookes is noted for hiscathode ray studies, fundamental in the development ofatomic physics. His researches on electrical discharges through a rarefied gas led him to observe the dark space around the cathode, now called the Crookes dark space. He demonstrated that cathode rays travel in straight lines and produce phosphorescence and heat when they strike certain materials. A pioneer of vacuum tubes, Crookes invented theCrookes tube – an early experimental discharge tube, with partial vacuum with which he studied the behavior of cathode rays. With the introduction ofspectrum analysis byRobert Bunsen andGustav Kirchhoff (1859–1860), Crookes applied the new technique to the study ofselenium compounds. Bunsen and Kirchhoff had previously used spectroscopy as a means of chemical analysis to discovercaesium andrubidium. In 1861, Crookes used this process to discoverthallium in some seleniferous deposits. He continued work on that new element, isolated it, studied its properties, and in 1873 determined its atomic weight. During his studies of thallium, Crookes discovered the principle of theCrookes radiometer, a device that converts light radiation into rotary motion. The principle of this radiometer has found numerous applications in the development of sensitive measuring instruments.
In 1862,Alexander Parkes exhibitedParkesine, one of the earliestsynthetic polymers, at the International Exhibition in London. This discovery formed the foundation of the modernplastics industry. In 1864,Cato Maximilian Guldberg andPeter Waage, building on Claude Louis Berthollet's ideas, proposed thelaw of mass action. In 1865,Johann Josef Loschmidt determined the number of molecules in amole, later namedAvogadro's number.
In 1865, August Kekulé, based partially on the work of Loschmidt and others, established the structure of benzene as a six carbon ring with alternating single anddouble bonds. Kekulé's novel proposal for benzene's cyclic structure was much contested but was never replaced by a superior theory. This theory provided the scientific basis for the dramatic expansion of the German chemical industry in the last third of the 19th century. Kekulé is also famous for having clarified the nature of aromatic compounds, which are compounds based on the benzene molecule. In 1865,Adolf von Baeyer began work onindigo dye, a milestone in modern industrial organic chemistry which revolutionized the dye industry.
Swedish chemist and inventorAlfred Nobel found that whennitroglycerin was incorporated in an absorbent inert substance likekieselguhr (diatomaceous earth) it became safer and more convenient to handle, and this mixture he patented in 1867 asdynamite. Nobel later on combined nitroglycerin with various nitrocellulose compounds, similar tocollodion, but settled on a more efficient recipe combining another nitrate explosive, and obtained a transparent, jelly-like substance, which was a more powerful explosive than dynamite.Gelignite, or blasting gelatin, as it was named, was patented in 1876; and was followed by a host of similar combinations, modified by the addition ofpotassium nitrate and various other substances.
An important breakthrough in making sense of the list of known chemical elements (as well as in understanding the internal structure of atoms) wasDmitri Mendeleev's development of the first modernperiodic table, or the periodic classification of the elements. Mendeleev, a Russian chemist, felt that there was some type of order to the elements and he spent more than thirteen years of his life collecting data and assembling the concept, initially with the idea of resolving some of the disorder in the field for his students. Mendeleev found that, when all the known chemical elements were arranged in order of increasing atomic weight, the resulting table displayed a recurring pattern, or periodicity, of properties within groups of elements. Mendeleev's law allowed him to build up a systematic periodic table of all the 66 elements then known based on atomic mass, which he published inPrinciples of Chemistry in 1869. His first Periodic Table was compiled on the basis of arranging the elements in ascending order of atomic weight and grouping them by similarity of properties.
Mendeleev had such faith in the validity of the periodic law that he proposed changes to the generally accepted values for the atomic weight of a few elements and, in his version of the periodic table of 1871, predicted the locations within the table of unknown elements together with their properties. He even predicted the likely properties of three yet-to-be-discovered elements, which he calledekaboron (Eb), ekaaluminium (Ea), and ekasilicon (Es), which proved to be good predictors of the properties ofscandium,gallium, andgermanium, respectively, which each fill the spot in the periodic table assigned by Mendeleev.
At first the periodic system did not raise interest among chemists. However, with the discovery of the predicted elements, notably gallium in 1875, scandium in 1879, and germanium in 1886, it began to win wide acceptance. The subsequent proof of many of his predictions within his lifetime brought fame to Mendeleev as the founder of the periodic law. This organization surpassed earlier attempts at classification byAlexandre-Émile Béguyer de Chancourtois, who published the telluric helix, an early, three-dimensional version of the periodic table of the elements in 1862,John Newlands, who proposed the law of octaves (a precursor to the periodic law) in 1864, andLothar Meyer, who developed an early version of the periodic table with 28 elements organized byvalence in 1864. Mendeleev's table did not include any of thenoble gases, however, which had not yet been discovered. Gradually the periodic law and table became the framework for a great part of chemical theory. By the time Mendeleev died in 1907, he enjoyed international recognition and had received distinctions and awards from many countries.
In 1873,Jacobus Henricus van 't Hoff andJoseph Achille Le Bel, working independently, developed a model ofchemical bonding that explained the chirality experiments of Pasteur and provided a physical cause foroptical activity in chiral compounds.[94] van 't Hoff's publication, calledVoorstel tot Uitbreiding der Tegenwoordige in de Scheikunde gebruikte Structuurformules in de Ruimte, etc. (Proposal for the development of 3-dimensional chemical structural formulae) and consisting of twelve pages of text and one page of diagrams, gave the impetus to the development ofstereochemistry. The concept of the "asymmetrical carbon atom", dealt with in this publication, supplied an explanation of the occurrence of numerous isomers, inexplicable by means of the then current structural formulae. At the same time he pointed out the existence of relationship between optical activity and the presence of an asymmetrical carbon atom.
American mathematical physicistJ. Willard Gibbs's work on the applications ofthermodynamics was instrumental in transformingphysical chemistry into a rigorous deductive science. During the years from 1876 to 1878, Gibbs worked on the principles of thermodynamics, applying them to the complex processes involved in chemical reactions. He discovered the concept ofchemical potential, or the "fuel" that makes chemical reactions work. In 1876 he published his most famous contribution, "On the Equilibrium of Heterogeneous Substances", a compilation of his work on thermodynamics and physical chemistry which laid out the concept offree energy to explain the physical basis of chemical equilibria.[95] In these essays were the beginnings of Gibbs' theories of phases of matter: he considered each state of matter a phase, and each substance a component. Gibbs took all of the variables involved in a chemical reaction – temperature, pressure, energy, volume, and entropy – and included them in one simple equation known asGibbs' phase rule.
Within this paper was perhaps his most outstanding contribution, the introduction of the concept of free energy, now universally calledGibbs free energy in his honor. The Gibbs free energy relates the tendency of a physical or chemical system to simultaneously lower its energy and increase its disorder, orentropy, in a spontaneous natural process. Gibbs's approach allows a researcher to calculate the change in free energy in the process, such as in a chemical reaction, and how fast it will happen. Since virtually all chemical processes and many physical ones involve such changes, his work has significantly impacted both the theoretical and experiential aspects of these sciences. In 1877,Ludwig Boltzmann established statistical derivations of many important physical and chemical concepts, includingentropy, and distributions of molecular velocities in the gas phase.[96] Together with Boltzmann andJames Clerk Maxwell, Gibbs created a new branch of theoretical physics calledstatistical mechanics (a term that he coined), explaining the laws of thermodynamics as consequences of the statistical properties of large ensembles of particles. Gibbs also worked on the application of Maxwell's equations to problems in physical optics. Gibbs's derivation of the phenomenological laws of thermodynamics from the statistical properties of systems with many particles was presented in his highly influential textbookElementary Principles in Statistical Mechanics, published in 1902, a year before his death. In that work, Gibbs reviewed the relationship between the laws of thermodynamics and the statistical theory of molecular motions. The overshooting of the original function by partial sums ofFourier series at points of discontinuity is known as theGibbs phenomenon.
German engineerCarl von Linde's invention of a continuous process of liquefying gases in large quantities formed a basis for the modern technology ofrefrigeration and provided both impetus and means for conducting scientific research at low temperatures and very high vacuums. He developed adimethyl ether refrigerator (1874) and an ammonia refrigerator (1876). Though other refrigeration units had been developed earlier, Linde's were the first to be designed with the aim of precise calculations of efficiency. In 1895 he set up a large-scale plant for the production of liquid air. Six years later he developed a method for separating pure liquid oxygen from liquid air that resulted in widespread industrial conversion to processes utilizing oxygen (e.g., insteel manufacture). He founded the Linde plc, the world's largestindustrial gas company by market share and revenue.
In 1883,Svante Arrhenius developed anion theory to explain conductivity inelectrolytes.[98] In 1884,Jacobus Henricus van 't Hoff publishedÉtudes de Dynamique chimique (Studies in Dynamic Chemistry), a seminal study onchemical kinetics.[99] In this work, van 't Hoff entered for the first time the field of physical chemistry. Of great importance was his development of the general thermodynamic relationship between the heat of conversion and the displacement of the equilibrium as a result of temperature variation. At constant volume, the equilibrium in a system will tend to shift in such a direction as to oppose the temperature change which is imposed upon the system. Thus, lowering the temperature results in heat development while increasing the temperature results in heat absorption. This principle of mobile equilibrium was subsequently (1885) put in a general form byHenry Louis Le Chatelier, who extended the principle to include compensation, by change of volume, for imposed pressure changes. The van 't Hoff-Le Chatelier principle, or simplyLe Chatelier's principle, explains the response ofdynamicchemical equilibria to external stresses.[100]
In 1884,Hermann Emil Fischer proposed the structure ofpurine, a key structure in many biomolecules, which he later synthesized in 1898. He also began work on the chemistry ofglucose and relatedsugars.[101] In 1885,Eugen Goldstein named thecathode ray, later discovered to be composed of electrons, and thecanal ray, later discovered to be positive hydrogen ions that had been stripped of their electrons in acathode-ray tube; these would later be namedprotons.[102] The year 1885 also saw the publishing of J. H. van 't Hoff'sL'Équilibre chimique dans les Systèmes gazeux ou dissous à I'État dilué (Chemical equilibria in gaseous systems or strongly diluted solutions), which dealt with this theory of dilute solutions. Here he demonstrated that the "osmotic pressure" in solutions which are sufficiently dilute is proportionate to theconcentration and the absolute temperature so that this pressure can be represented by a formula that only deviates from the formula for gas pressure by a coefficienti. He also determined the value ofi by various methods, for example by means of thevapor pressure andFrançois-Marie Raoult's results on the lowering of the freezing point. Thus van 't Hoff was able to prove that thermodynamic laws are not only valid for gases, but also for dilute solutions. His pressure laws, given general validity by the electrolytic dissociation theory of Arrhenius (1884–1887) – the first foreigner who came to work with him in Amsterdam (1888) – are considered the most comprehensive and important in the realm of natural sciences. In 1893,Alfred Werner discovered the octahedral structure of cobalt complexes, thus establishing the field ofcoordination chemistry.[103]
The most celebrated discoveries of Scottish chemistWilliam Ramsay were made in inorganic chemistry. Ramsay was intrigued by the British physicistJohn Strutt, 3rd Baron Rayleigh's 1892 discovery that the atomic weight ofnitrogen found in chemical compounds was lower than that of nitrogen found in the atmosphere. He ascribed this discrepancy to a light gas included in chemical compounds of nitrogen, while Ramsay suspected a hitherto undiscovered heavy gas in atmospheric nitrogen. Using two different methods to remove all known gases from air, Ramsay and Lord Rayleigh were able to announce in 1894 that they had found a monatomic, chemically inert gaseous element that constituted nearly 1 percent of the atmosphere; they named itargon.
The following year, Ramsay liberated another inert gas from a mineral calledcleveite; this proved to behelium, previously known only in the solar spectrum. In his bookThe Gases of the Atmosphere (1896), Ramsay showed that the positions of helium and argon in the periodic table of elements indicated that at least three more noble gases might exist. In 1898 Ramsay and the British chemistMorris W. Travers isolated these elements—calledneon,krypton, andxenon—from air and brought them to a liquid state at low temperature and high pressure. Sir William Ramsay worked withFrederick Soddy to demonstrate, in 1903, that alpha particles (helium nuclei) were continually produced during the radioactive decay of a sample of radium. Ramsay was awarded the 1904Nobel Prize for Chemistry in recognition of "services in the discovery of the inert gaseous elements in the air, and his determination of their place in the periodic system."
In 1897,J. J. Thomson discovered theelectron using the cathode-ray tube. In 1898,Wilhelm Wien demonstrated that canal rays (streams of positive ions) can be deflected by magnetic fields and that the amount of deflection is proportional to themass-to-charge ratio. This discovery would lead to theanalytical technique known asmass spectrometry in 1912.[104]
Marie Skłodowska-Curie was a Polish-born French physicist and chemist who is famous for her pioneering research onradioactivity. She and her husband are considered to have laid the cornerstone of the nuclear age with their research on radioactivity. Marie was fascinated with the work ofHenri Becquerel, a French physicist who discovered in 1896 that uranium casts off rays similar to theX-rays discovered byWilhelm Röntgen. Marie Curie began studying uranium in late 1897 and theorized, according to a 1904 article she wrote forCentury magazine, "that the emission of rays by the compounds of uranium is a property of the metal itself—that it is an atomic property of the element uranium independent of its chemical or physical state." Curie took Becquerel's work a few steps further, conducting her own experiments on uranium rays. She discovered that the rays remained constant, no matter the condition or form of the uranium. The rays, she theorized, came from the element's atomic structure. This revolutionary idea created the field ofatomic physics and the Curies coined the wordradioactivity to describe the phenomenon.
Pierre and Marie further explored radioactivity by working to separate the substances in uranium ores and then using theelectrometer to make radiation measurements to 'trace' the minute amount of unknown radioactive element among the fractions that resulted. Working with the mineralpitchblende, the pair discovered a new radioactive element in 1898. They named the elementpolonium, after Marie's native country of Poland. On December 21, 1898, the Curies detected the presence of another radioactive material in the pitchblende. They presented this finding to theFrench Academy of Sciences on December 26, proposing that the new element be calledradium. The Curies then went to work isolating polonium and radium from naturally occurring compounds to prove that they were new elements. In 1902, the Curies announced that they had produced a decigram of pure radium, demonstrating its existence as a unique chemical element. While it took three years for them to isolate radium, they were never able to isolate polonium. Along with the discovery of two new elements and finding techniques for isolating radioactive isotopes, Curie oversaw the world's first studies into the treatment ofneoplasms, using radioactive isotopes. With Henri Becquerel and her husband, Pierre Curie, she was awarded the 1903Nobel Prize for Physics. She was the sole winner of the 1911Nobel Prize for Chemistry. She was the first woman to win a Nobel Prize, and she is the only woman to win the award in two different fields.
While working with Marie to extract pure substances from ores, an undertaking that really required industrial resources but that they achieved in relatively primitive conditions, Pierre himself concentrated on the physical study (including luminous and chemical effects) of the new radiations. Through the action of magnetic fields on the rays given out by the radium, he proved the existence of particles that were electrically positive, negative, and neutral; theseErnest Rutherford was afterward to call alpha, beta, and gamma rays. Pierre then studied these radiations bycalorimetry and also observed the physiological effects of radium, thus opening the way to radium therapy. Among Pierre Curie's discoveries were that ferromagnetic substances exhibited a critical temperature transition, above which the substances lost their ferromagnetic behavior – this is known as the "Curie point." He was elected to the Academy of Sciences (1905), having in 1903 jointly with Marie received the Royal Society's prestigious Davy Medal and jointly with her and Becquerel the Nobel Prize for Physics. He was run over by a carriage in therue Dauphine in Paris in 1906 and died instantly. His complete works were published in 1908.
New Zealand-born chemist and physicistErnest Rutherford is considered to be "the father ofnuclear physics." Rutherford is best known for devising the namesalpha,beta, andgamma to classify various forms of radioactive "rays" which were poorly understood at his time (alpha and beta rays are particle beams, while gamma rays are a form of high-energyelectromagnetic radiation). Rutherford deflected alpha rays with both electric and magnetic fields in 1903. Working withFrederick Soddy, Rutherford explained thatradioactivity is due to thetransmutation of elements, now known to involvenuclear reactions.
He also observed that the intensity of radioactivity of a radioactive element decreases over a unique and regular amount of time until a point of stability, and he named the halving time the "half-life". In 1901 and 1902 he worked with Frederick Soddy to prove that atoms of one radioactive element would spontaneously turn into another, by expelling a piece of the atom at high velocity. In 1906 at the University of Manchester, Rutherford oversaw an experiment conducted by his studentsHans Geiger (known for theGeiger counter) andErnest Marsden. In theGeiger–Marsden experiment, a beam of alpha particles, generated by the radioactive decay ofradon, was directed normally onto a sheet of very thin gold foil in an evacuated chamber. Under the prevailingplum pudding model, the alpha particles should all have passed through the foil and hit the detector screen, or have been deflected by, at most, a few degrees.
However, the actual results surprised Rutherford. Although many of the alpha particles did pass through as expected, many others were deflected at small angles while others were reflected back to the alpha source. They observed that a very small percentage of particles were deflected through angles much larger than 90 degrees. The gold foil experiment showed large deflections for a small fraction of incident particles. Rutherford realized that, because some of the alpha particles were deflected or reflected, the atom had a concentrated centre of positive charge and of relatively large mass – Rutherford later termed this positive center the "atomic nucleus". The alpha particles had either hit the positive centre directly or passed by it close enough to be affected by its positive charge. Since many other particles passed through the gold foil, the positive centre would have to be a relatively small size compared to the rest of the atom – meaning that the atom is mostly open space. From his results, Rutherford developed a model of the atom that was similar to theSolar System, known as theRutherford model. Like planets, electrons orbited a central, Sun-like nucleus. For his work with radiation and the atomic nucleus, Rutherford received the 1908 Nobel Prize in Chemistry.
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In 1903,Mikhail Tsvet inventedchromatography, an important analytic technique. In 1904,Hantaro Nagaoka proposed an early nuclear model of the atom, where electrons orbit a dense massive nucleus. In 1905,Fritz Haber andCarl Bosch developed theHaber process for makingammonia, a milestone in industrial chemistry with deep consequences in agriculture. The Haber process, or Haber–Bosch process, combinednitrogen andhydrogen to form ammonia in industrial quantities for the production of fertilizer and munitions. The food production for half the world's current population depends on this method for producing fertilizer. Haber, along withMax Born, proposed theBorn–Haber cycle as a method for evaluating the lattice energy of an ionic solid. Haber has also been described as the "father ofchemical warfare" for his work developing and deploying chlorine and other poisonous gases during World War I.
In 1905,Albert Einstein explainedBrownian motion in a way that definitively proved atomic theory.Leo Baekeland inventedbakelite, one of the first commercially successful plastics. In 1909, American physicistRobert Andrews Millikan – who had studied in Europe underWalther Nernst andMax Planck – measured the charge of individual electrons with unprecedented accuracy through theoil drop experiment, in which he measured the electric charges on tiny falling water (and later oil) droplets. His study established that any particular droplet's electrical charge is a multiple of a definite, fundamental value—the electron's charge—and thus a confirmation that all electrons have the same charge and mass. Beginning in 1912, he spent several years investigating and finally proving Albert Einstein's proposed linear relationship between energy and frequency, and providing the first directphotoelectric support for thePlanck constant. In 1923 Millikan was awarded the Nobel Prize for Physics.
In 1909,S. P. L. Sørensen invented thepH concept and developed methods for measuring acidity. In 1911,Antonius Van den Broek proposed the idea that the elements on the periodic table are more properly organized by positive nuclear charge rather than atomic weight. In 1911, the firstSolvay Conference was held in Brussels, bringing together most of the most prominent scientists of the day. In 1912,William Henry Bragg andWilliam Lawrence Bragg proposedBragg's law and established the field ofX-ray crystallography, an important tool for elucidating the crystal structure of substances. In 1912,Peter Debye used the concept of a molecular dipole to describe asymmetric charge distribution in some molecules.
Otto Hahn was a Germanchemist and a pioneer in the fields ofradioactivity andradiochemistry. He played a leading role in the discovery ofnuclear fission and establishednuclear chemistry as a scientic field. Hahn,Lise Meitner andFritz Strassmann discovered radioactiveisotopes of radium,thorium,protactinium anduranium. He also discovered the phenomena ofatomic recoil andnuclear isomerism, and pioneeredrubidium–strontium dating. In 1938, Hahn, Meitner and Strassmanndiscovered nuclear fission. In their second publication on nuclear fission in February 1939, Hahn and Strassmann predicted the existence and liberation of additional neutrons during the fission process, opening up the possibility of anuclear chain reaction. Hahn received the 1944Nobel Prize for Chemistry for the discoveries.Nuclear fission was the basis fornuclear reactors andnuclear weapons.
In 1913,Niels Bohr, a Danish physicist, introduced the concepts ofquantum mechanics to atomic structure by proposing what is now known as theBohr model of the atom, where electrons exist only in strictly defined circular orbits around the nucleus similar to rungs on a ladder. The Bohr Model is a planetary model in which the negatively charged electrons orbit a small, positively charged nucleus similar to the planets orbiting the Sun (except that the orbits are not planar) – the gravitational force of the solar system is mathematically akin to the attractive Coulomb (electrical) force between the positively charged nucleus and the negatively charged electrons.
In the Bohr model, however, electrons orbit the nucleus in orbits that have a set size and energy – the energy levels are said to bequantized, which means that only certain orbits with certain radii are allowed; orbits in between simply do not exist. The energy of the orbit is related to its size – that is, the lowest energy is found in the smallest orbit. Bohr also postulated that electromagnetic radiation is absorbed or emitted when an electron moves from one orbit to another. Because only certain electron orbits are permitted, the emission of light accompanying a jump of an electron from an excited energy state to ground state produces a uniqueemission spectrum for each element. Bohr later received the Nobel Prize in physics for this work.
Niels Bohr also worked on the principle ofcomplementarity, which states that an electron can be interpreted in two mutually exclusive and valid ways. Electrons can be interpreted as wave or particle models. His hypothesis was that an incoming particle would strike the nucleus and create an excited compound nucleus. This formed the basis of hisliquid drop model and later provided a theory base fornuclear fission after itsdiscovery by chemistsOtto Hahn andFritz Strassman, and explanation and naming by physicistsLise Meitner andOtto Frisch.
In 1913,Henry Moseley, working from Van den Broek's earlier idea, introduced the concept of atomic number to fix some inadequacies of Mendeleev's periodic table, which had been based on atomic weight. The peak of Frederick Soddy's career in radiochemistry was in 1913 with his formulation of the concept ofisotopes, which stated that certain elements exist in two or more forms which have different atomic weights but which are indistinguishable chemically. He is remembered for proving the existence of isotopes of certain radioactive elements, and is also credited, along with others, with the discovery of the elementprotactinium in 1917. In 1913, J. J. Thomson expanded on the work of Wien by showing that charged subatomic particles can be separated by their mass-to-charge ratio, a technique known asmass spectrometry.
American physical chemistGilbert N. Lewis laid the foundation ofvalence bond theory; he was instrumental in developing a bonding theory based on the number of electrons in the outermost "valence" shell of the atom. In 1902, while Lewis was trying to explain valence to his students, he depicted atoms as constructed of a concentric series of cubes with electrons at each corner. This "cubic atom" explained the eight groups in the periodic table and represented his idea that chemical bonds are formed by electron transference to give each atom a complete set of eight outer electrons (an "octet").
Lewis's theory of chemical bonding continued to evolve and, in 1916, he published his seminal article "The Atom of the Molecule", which suggested that a chemical bond is a pair of electrons shared by two atoms. Lewis's model equated the classicalchemical bond with the sharing of a pair of electrons between the two bonded atoms. Lewis introduced the "electron dot diagrams" in this paper to symbolize the electronic structures of atoms and molecules. Now known asLewis structures, they are discussed in virtually every introductory chemistry book.
Shortly after the publication of his 1916 paper, Lewis became involved with military research. He did not return to the subject of chemical bonding until 1923, when he masterfully summarized his model in a short monograph entitled Valence and the Structure of Atoms and Molecules. His renewal of interest in this subject was largely stimulated by the activities of the American chemist and General Electric researcherIrving Langmuir, who between 1919 and 1921 popularized and elaborated Lewis's model. Langmuir subsequently introduced the termcovalent bond. In 1921,Otto Stern andWalther Gerlach established the concept of quantum mechanical spin in subatomic particles.
For cases where no sharing was involved, Lewis in 1923 developed the electron pair theory ofacids andbase: Lewis redefined an acid as any atom or molecule with an incomplete octet that was thus capable of accepting electrons from another atom; bases were, of course, electron donors. His theory is known as the concept ofLewis acids and bases. In 1923, G. N. Lewis andMerle Randall publishedThermodynamics and the Free Energy of Chemical Substances, first modern treatise on chemicalthermodynamics.
The 1920s saw a rapid adoption and application of Lewis's model of the electron-pair bond in the fields of organic and coordination chemistry. In organic chemistry, this was primarily due to the efforts of the British chemistsArthur Lapworth,Robert Robinson,Thomas Lowry, andChristopher Ingold; while in coordination chemistry, Lewis's bonding model was promoted through the efforts of the American chemistMaurice Huggins and the British chemistNevil Sidgwick.
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| From left to right, top row:Louis de Broglie (1892–1987) andWolfgang Pauli (1900–1958); second row:Erwin Schrödinger (1887–1961) andWerner Heisenberg (1901–1976) |
In 1924, French quantum physicistLouis de Broglie published his thesis, in which he introduced a revolutionary theory of electron waves based onwave–particle duality. In his time, the wave and particle interpretations of light andmatter were seen as being at odds with one another, but de Broglie suggested that these seemingly different characteristics were instead the same behavior observed from different perspectives—that particles can behave like waves, and waves (radiation) can behave like particles. Broglie's proposal offered an explanation of the restricted motion ofelectrons within the atom. The first publications of Broglie's idea of "matter waves" had drawn little attention from other physicists, but a copy of his doctoral thesis chanced to reach Einstein, whose response was enthusiastic. Einstein stressed the importance of Broglie's work both explicitly and by building further on it.
In 1925, Austrian-born physicistWolfgang Pauli developed thePauli exclusion principle, which states that no two electrons around a single nucleus in an atom can occupy the samequantum state simultaneously, as described by fourquantum numbers. Pauli made major contributions to quantum mechanics and quantum field theory – he was awarded the 1945 Nobel Prize for Physics for his discovery of the Pauli exclusion principle – as well as solid-state physics, and he successfully hypothesized the existence of theneutrino. In addition to his original work, he wrote masterful syntheses of several areas of physical theory that are considered classics of scientific literature.
In 1926 at the age of 39, Austrian theoretical physicistErwin Schrödinger produced the papers that gave the foundations of quantum wave mechanics. In those papers he described his partial differential equation that is the basic equation of quantum mechanics and bears the same relation to the mechanics of the atom asNewton's equations of motion bear to planetary astronomy. Adopting a proposal made by Louis de Broglie in 1924 that particles of matter have a dual nature and in some situations act like waves, Schrödinger introduced a theory describing the behaviour of such a system by a wave equation that is now known as theSchrödinger equation. The solutions to Schrödinger's equation, unlike the solutions to Newton's equations, are wave functions that can only be related to the probable occurrence of physical events. The readily visualized sequence of events of the planetary orbits of Newton is, in quantum mechanics, replaced by the more abstract notion ofprobability. (This aspect of the quantum theory made Schrödinger and several other physicists profoundly unhappy, and he devoted much of his later life to formulating philosophical objections to the generally accepted interpretation of the theory that he had done so much to create.)
German theoretical physicistWerner Heisenberg was one of the key creators of quantum mechanics. In 1925, Heisenberg discovered a way to formulate quantum mechanics in terms of matrices. For that discovery, he was awarded the Nobel Prize for Physics for 1932. In 1927 he published hisuncertainty principle, upon which he built his philosophy and for which he is best known. Heisenberg was able to demonstrate that if you were studying an electron in an atom you could say where it was (the electron's location) or where it was going (the electron's velocity), but it was impossible to express both at the same time. He also made important contributions to the theories of thehydrodynamics ofturbulent flows, the atomic nucleus,ferromagnetism,cosmic rays, andsubatomic particles, and he was instrumental in planning the first West Germannuclear reactor atKarlsruhe, together with aresearch reactor in Munich, in 1957. Considerable controversy surrounds his work on atomic research during World War II.
Some view the birth of quantum chemistry in the discovery of theSchrödinger equation and its application to thehydrogen atom in 1926.[citation needed] However, the 1927 article ofWalter Heitler andFritz London[107] is often recognised as the first milestone in the history of quantum chemistry. This is the first application ofquantum mechanics to the diatomichydrogen molecule, and thus to the phenomenon of thechemical bond. In the following years much progress was accomplished byEdward Teller,Robert S. Mulliken,Max Born,J. Robert Oppenheimer,Linus Pauling,Erich Hückel,Douglas Hartree andVladimir Aleksandrovich Fock, to cite a few.[citation needed]
Still, skepticism remained as to the general power of quantum mechanics applied to complex chemical systems.[citation needed] The situation around 1930 is described byPaul Dirac:[108]
The underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are thus completely known, and the difficulty is only that the exact application of these laws leads to equations much too complicated to be soluble. It therefore becomes desirable that approximate practical methods of applying quantum mechanics should be developed, which can lead to an explanation of the main features of complex atomic systems without too much computation.
Hence the quantum mechanical methods developed in the 1930s and 1940s are often referred to as theoreticalmolecular oratomic physics to underline the fact that they were more the application of quantum mechanics to chemistry andspectroscopy than answers to chemically relevant questions. In 1951, a milestone article in quantum chemistry is the seminal paper ofClemens C. J. Roothaan onRoothaan equations.[109] It opened the avenue to the solution of theself-consistent field equations for small molecules likehydrogen ornitrogen. Those computations were performed with the help of tables of integrals which were computed on the most advanced computers of the time.[citation needed]
In the 1940s many physicists turned frommolecular oratomic physics tonuclear physics (likeJ. Robert Oppenheimer orEdward Teller).Glenn T. Seaborg was an American nuclear chemist best known for his work on isolating and identifyingtransuranium elements (those heavier thanuranium). He shared the 1951 Nobel Prize for Chemistry withEdwin Mattison McMillan for their independent discoveries of transuranium elements.Seaborgium was named in his honour, making him the only person, along withAlbert Einstein andYuri Oganessian, for whom a chemical element was named during his lifetime.
By the mid 20th century, in principle, the integration of physics and chemistry was extensive, with chemical properties explained as the result of theelectronic structure of theatom;Linus Pauling's book onThe Nature of the Chemical Bond used the principles of quantum mechanics to deducebond angles in ever-more complicated molecules. However, though some principles deduced from quantum mechanics were able to predict qualitatively some chemical features for biologically relevant molecules, they were, till the end of the 20th century, more a collection of rules, observations, and recipes than rigorousab initio quantitative methods.[citation needed]
This heuristic approach triumphed in 1953 whenJames Watson andFrancis Crick deduced the double helical structure ofDNA by constructing models constrained by and informed by the knowledge of the chemistry of the constituent parts and theX-ray diffraction patterns obtained byRosalind Franklin.[110] This discovery lead to an explosion of research into thebiochemistry of life.
In the same year, theMiller–Urey experiment demonstrated that basic constituents ofprotein, simpleamino acids, could themselves be built up from simpler molecules in asimulation of primordialprocesses on Earth. This first attempt by chemists to study hypothetical processes in the laboratory under controlled conditions helped kickstart bountiful research, within thenatural sciences, into theorigins of life.
In 1983Kary Mullis devised a method for the in-vitro amplification of DNA, known as thepolymerase chain reaction (PCR), which revolutionized the chemical processes used in the laboratory to manipulate it. PCR could be used to synthesize specific pieces of DNA and made possible thesequencing of DNA of organisms, which culminated in the hugehuman genome project.
An important piece in the double helix puzzle was solved by one of Pauling's studentsMatthew Meselson andFrank Stahl, the result of their collaboration (Meselson–Stahl experiment) has been called as "the most beautiful experiment in biology".
They used a centrifugation technique that sorted molecules according to differences in weight. Because nitrogen atoms are a component of DNA, they were labelled and therefore tracked in replication in bacteria.
In 1970,John Pople developed theGaussian program greatly easingcomputational chemistry calculations.[111] In 1971,Yves Chauvin offered an explanation of the reaction mechanism ofolefin metathesis reactions.[112] In 1975,Karl Barry Sharpless and his group discovered stereoselectiveoxidation reactions includingSharpless epoxidation,[113][114]Sharpless asymmetric dihydroxylation,[115][116][117] andSharpless oxyamination.[118][119][120]In 1985,Harold Kroto,Robert Curl andRichard Smalley discoveredfullerenes, a class of large carbon molecules superficially resembling thegeodesic dome designed by architectR. Buckminster Fuller.[121] In 1991,Sumio Iijima usedelectron microscopy to discover a type of cylindrical fullerene known as acarbon nanotube, though earlier work had been done in the field as early as 1951. This material is an important component in the field ofnanotechnology.[122] In 1994,K. C. Nicolaou with his group[123][124] andRobert A. Holton and his group, achieved the firsttotal synthesis of Taxol.[125][126][127] In 1995,Eric Cornell andCarl Wieman produced the firstBose–Einstein condensate, a substance that displays quantum mechanical properties on the macroscopic scale.[128]
Before the 20th century, chemistry was defined as the science of the nature of matter and its transformations. It was therefore distinct from physics which was not concerned with such dramatic transformation of matter. Moreover, in contrast to physics, chemistry remained predominantly a descriptive and empirical science until the end of the 19th century. Though they developed a consistent quantitative foundation based on notions of atomic and molecular weights, combining proportions, and thermodynamic quantities, chemists had less use of advanced mathematics.[129] Some even expressed reluctance about the use of mathematics within chemistry. For example, the philosopherAuguste Comte wrote in 1830:
Every attempt to employ mathematical methods in the study of chemical questions must be considered profoundly irrational and contrary to the spirit of chemistry.... if mathematical analysis should ever hold a prominent place in chemistry – an aberration which is happily almost impossible – it would occasion a rapid and widespread degeneration of that science.
However, in the second part of the 19th century, the situation began to change asAugust Kekulé wrote in 1867:
I rather expect that we shall someday find a mathematico-mechanical explanation for what we now call atoms which will render an account of their properties.
As understanding of the nature of matter has evolved, so too has the self-understanding of the science of chemistry by its practitioners. This continuing historical process of evaluation includes the categories, terms, aims and scope of chemistry. Additionally, the development of the social institutions and networks which support chemical enquiry are highly significant factors that enable the production, dissemination and application of chemical knowledge. (SeePhilosophy of chemistry)
The later part of the nineteenth century saw a huge increase in the exploitation ofpetroleum extracted from the earth for the production of a host of chemicals and largely replaced the use ofwhale oil,coal tar andnaval stores used previously. Large-scale production andrefinement of petroleum provided feedstocks forliquid fuels such asgasoline anddiesel,solvents,lubricants,asphalt,waxes, and for the production of many of the common materials of the modern world, such as syntheticfibers, plastics,paints,detergents,pharmaceuticals,adhesives andammonia asfertilizer and for other uses. Many of these required newcatalysts and the utilization ofchemical engineering for their cost-effective production.[citation needed]
In the mid-twentieth century, control of the electronic structure ofsemiconductor materials was made precise by the creation of large ingots of extremely pure single crystals ofsilicon andgermanium. Accurate control of their chemical composition by doping with other elements made the production of the solid statetransistor in 1951 and made possible the production of tinyintegrated circuits for use in electronic devices, especiallycomputers.[citation needed]
listed chronologically:
{{cite journal}}: CS1 maint: DOI inactive as of November 2024 (link)"Something has been said about the chemical excellence ofcast iron in ancient India, and about the high industrial development of theGupta times, when India was looked to, even byImperial Rome, as the most skilled of the nations in such chemicalindustries asdyeing,tanning,soap-making, glass andcement... By the sixth century the Hindus were far ahead of Europe in industrial chemistry; they were masters ofcalcinations,distillation,sublimation,steaming,fixation, the production of light without heat, the mixing ofanesthetic andsoporific powders, and the preparation of metallicsalts,compounds andalloys. 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 fromAlexander, 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 thePersians, and by the Persians from India."
"Two systems ofHindu thought propoundphysical theories suggestively similar to those ofGreece.Kanada, founder of theVaisheshika philosophy, held that the world was composed of atoms as many in kind as the various elements. TheJains more nearly approximated toDemocritus by teaching that all atoms were of the same kind, producing different effects by diverse modes of combinations. Kanada believed light and heat to be varieties of the same substance;Udayana taught that all heat comes from the sun; andVachaspati, likeNewton, interpreted light as composed of minute particles emitted by substances and striking the eye."
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