ARTICLE

AN INTRODUCTION TO THE HISTORY OF

N. R. DAS*

The word chemistry originated from the term, chemi or kima, the name of Egypt in Egyptian. The time period for the covers from ancient history of chemistry to the present. In earliest civilizations, fire was accepted as a mystical force and the controlled use fire in their familiar regular practices like cooking, lighting, making of earthen and glass wares, , wines, metallurgy, armours, etc. eventually resulted in the development of various branches of chemistry in the later period. The basic chemical hypothesis was first propounded by Aristotle with his theory of four fundamental elements, fire, earth, and air, from which everything was formed as a combination. In medieval around 300 B. C., the arts of alchemy being intermingled with magic and occultism proliferated into natural science with the goal of transmuting cheap metals into precious gold with ‘Philosopher’s Stone’ and of chemical concoction, ‘The ’, for a longer and cured life. In seventeenth century, was the first to make a clear differentiation between alchemy and scientific experimental approach towards matter initiating the trend of the history of modern chemistry. The pioneering contributions of Antoine Lavoisier and Jons Berzelius established the subject of chemistry on proper experimental and theoretical footings of chemical science. In the later period, with important discoveries and rapid advancement in research and technologies, in general, the subject of chemistry has been expanded into different broad groups as well as in cross-disciplinary and specialized fields of chemical science depending on the type and kind of matter being investigated. Chemistry is now a major branch of physical science.

Introduction of chemistry, , metallurgy, astronomy, philosophy, astrology and mysticism, as parts of normal behaviour in n early civilizations, thinkers were those who always different regions of the world, were known as Alchemy. search for the logic regarding the existence of the An alchemist was later designated as a ‘chemist’ and in surrounding materials and tried to identify the basic I describing the activities of the chemists, the suffix ‘-ry’ elements comprising the natural substances. The ancient was added to the word chemist, to assign the subject as Greek, Indian, Mayan, Chinese and other philosophies ‘chemistry’. attempted to postulate appropriate hypothesis for the existence of the natural materials in solid, liquid or gaseous The etymology or the origin of the word chemistry is phases having different characteristic properties of density, much disputed as the science of chemistry has been around colour, smell, etc. as well as their changing behaviours in since the prehistoric times. The visions on the composition the prevailing environmental conditions. and properties of matter were to some extent shared by both alchemy and chemistry and a blend of these was In the history of chemistry as early as around 300 B. presented earlier by the term chymistry. Robert Boyle in C., the regular skilful practices involving various techniques 1661 was the first to use the term chymistry to specify the subject dealing with the material principles of mixed * Former Professor, Saha Institute of Nuclear Physics, 1/AF, Bidhan bodies. According to Christopher Glaser (1663), chymistry Nagar, Kolkata - 700 064, e-mail : [email protected]

342 SCIENCE AND CULTURE, NOVEMBER-DECEMBER, 2016 meant to acquire scientific knowledge of dissolving a light was accepted simply as a mystical force. Early substance, to draw from it another substance of different evidence of extractive metallurgy dated fifth and sixth composition and to exalt it to a higher perfection. In 1730, millennium B. C. involving lead and copper was found in Georg Ernst Stahl was perhaps the first to use the word different archaeological sites in Siberia and of the third chemistry to describe the technique of resolving mixed, millennium B. C. in Portugal, and United Kingdom. aggregate or compound materials into their principles and The controlled use of fire in various aspects of cooking of composing these materials from those principles. Jean- and habitat lighting; making of glass and earthen wares Baptiste Dumas in 1837 referred chemistry to deal with like pottery, bricks, glazes; of beers and wines; the science concerning the laws and the effects of molecular preparation of medicines, soaps, perfumes; extraction of forces. chemicals from plants; etc. eventually formed the basis for development of different branches of chemistry in the later In retrospect, with new discoveries and development period of around 1000 B. C. of theories in chemical science, the definition of chemistry has gradually been modified over the period. For example, The application of fire for extraction and purification Linus Pauling in 1947 suggested that the chemistry is to of metals from ores, production of alloys like bronze, deal with the science of substances involving their structure, making of armors and weapons for the armies from superior properties and the reactions that change them into other alloys, etc. resulted in the initiation of the field of substances. More recently in 1998, the definition of metallurgy which helped in the development of early human chemistry has been broadly modified to mean the study of culture. In the Bronze Age around 3500 B.C., significant matter and the changes it undergoes, as phrased by progress in alchemy involving metallurgy was achieved in Professor Raymond Chang. The subject of chemistry has ancient India. The Iron Age began with the development now become a major branch of physical science primarily of the method for extraction of metal iron from its ores by concerned with atoms, molecules and their interactions and Hittites in about 1200 B.C. Wide varieties of evidences of transformations involving the structure, composition and early civilizations in different regions of the world properties of matter. With rapid advancement of science, particularly in ancient and medieval kingdoms and empires the subject of chemistry, in the later period, has become of the Middle East, Iran, Egypt, Anatolia (Turkey), Greeks, intertwined with the modern topic like thermodynamics, Romans, Europe, China, India, Japan, amongst others, have nuclear science and many other fields of advanced research, indicated the cultural developments in this age period. The particularly, in occupying an intermediate position between new prehistoric discoveries are continuous and ongoing. physics and biology. The early theory of atomism has been traced back to In this article, the time span for the History of ancient Greece and ancient India. The Greek philosophers, Chemistry representing from the ancient period to the Democritus and Epicurus, around 440 B.C, proclaimed that present is chronologically classified into four broad the simplest unit of matter is the atom and all matter is categories such as Ancient Period of the History of composed of these indivisible and indestructible atoms. The Chemistry, Medieval Alchemy, Early Chemistry of 17th and proclamation was found to be corroborated with the views 18th Centuries, and Chemistry of 19th Century to the of the Indian philosopher, Kanada, the founder of the Present. Vaisheshika philosophy, around the same time period. In 380 B. C, the Greek thinker, Polybus postulated that the Ancient Period of History human body is composed of four humours, the four fluids The earliest evidence of using metal by humans as free of the body, believed to determine the physical and mental ‘native’ gold has been manifested from the fact that small qualities of human. Epicurus around 300 B.C. suggested a amounts of natural gold have been found in Spanish caves universe of indestructible atoms in which man himself has of the late Paleolithic period of around 40,000 B. C. In the capability of achieving a balanced life. ancient Egypt, as early as in 2900 B.C., gold was In early civilizations, the familiar practices of arts or considered as precious metal and the metals like silver, the skilled techniques were followed without any basic copper, tin which can also be sometimes found native were knowledge or a systematic concept. In 300 B.C., a chemical used in metal working in the prevailing cultures. Egyptian hypothesis was first propounded by Aristotle in Greece with weapons made from meteoric iron in about 3000 B.C. were the theory of four fundamental elements, fire (hot and dry), known as ‘Daggers from Heaven’. water (cold and moist), air (hot and moist) and earth (cold In early societies, the fire that was generally utilized and dry), as presented in Figure 1, in which everything to transform one substance into another producing heat and was considered to be formed as a combination of these

VOL. 82, NOS. 11–12 343 elements. Empedocles also hinted a hypothesis about the ahead of many of the existing civilizations during the theory of fundamental elements earlier in 420 B. C. The period. In ninth century, the inventions of laboratory Roman poet and philosopher Lucretius in 50 B. C. wrote apparatus like alembic (apparatus for distilling), crucible, ‘De Rerum Natura (The of Things)’ which retort, furnace; chemical analysis of substances; distinction described the principles of atomism; the nature of mind between acids and alkalis; manufacture of drugs; etc. were and soul; cause of sensation and thought; the development achieved in chemistry. of the world and explanations for a variety of celestial and terrestrial phenomena. Alchemy made extensive contribution to the evolution of chemistry in Greco-Roman Egypt, India and the Arab world and the Western alchemists, in general, became influenced by the scientific experimental framework developed in these regions, as the discipline migrated to Renaissance Europe in twelfth century. In Europe, Fire Water Air Earth (1493–1541) refuted the four element theory of Figure 1. Symbol of basic alchemy Aristotle and introduced a hybrid of alchemy and science called as . In 1556, Georg Agricola, known Medieval Alchemy as the ‘father of metallurgy’, through his presentation of The word alchemy was derived from the the processes for mining of metal ores and refining of Arabic synonym, al-kîmîâ which might have been originated metals by smelting in ‘De re metallica’, tried to remove from the word Chemi or Kimi, the ancient name of Egypt the mysticism associated with the subject. Several chemists in Egyptian. In the Hellenistic world, (related to Greek contradicted the theories of alchemy and hinted for the culture from 323 B. C. to 31 B.C.), the art of alchemy version of the conservation of mass suggesting that a being intermingled with magic and occultism proliferated material body is capable of changing but can’t disappear. first into the study of natural substances with the ultimate A fraudulent side of alchemy was exposed, especially goal of transmuting common cheap metals into attractive in manufacturing of counterfeit gold from cheap substances, gold or silver with ‘Philosopher’s Stone’ and inventing a in ‘Canon’s Yeoman’s Tale’ of Geoffrey Chaucer. In 1317, chemical concoction, ‘The Elixir of Life’, that would enable the Avignon Pope John XXII ordered the alchemists to people to live longer and cure all ailments. In alchemy, leave for the misdeeds. In in 1403 the act known metals were considered in conjunction with heavenly of ‘ of metals’ was declared punishable by bodies. death. In spite of such extreme measures, some group of The advent of alchemy was greatly influenced by the alchemists still sought to discover the ‘philosopher’s stone’ Aristotle’s theory of four fundamental elements along with and ‘the elixir of life’, which, however, never happened two more alchemical elements, namely, sulfur, as ‘the stone within the time period. which burns’ symbolizing the properties of flammability In alchemy, the alchemists although were not so or combustion, and mercury, characterizing the properties successful in elucidating the nature of matter or its of volatility and stability, and in addition, salt indicated transformation, but have set the trend of modern chemistry. the solidity. According to Swiss alchemist Paracelsus, the Since the beginning of the fourteenth century, the alchemists four element theory of Aristotle appeared in bodies as three in general became more conscious about the reproducibility fundamental metallic principles, the ‘tria prima’ of the of the scientific methods and experiments and felt the need alchemists. of specific vocabulary for systematic naming of the new In medieval alchemy during 300 B. C. to 300 A.D., compounds and the invented terminologies. During the the Persian alchemist, Jabir bin Hayyan, as ‘the father of period, along with popular exotic alchemy, the spiritual chemistry’, led the foundations of a systematic scientific alchemy was also flourished and realigned to its Platonic, approach towards the development of experimental Hermetic and Gnostic roots and the symbolic quest for the chemical research in the Arab World. Attempts were made philosopher’s stone still continued to be the domain of for classification of the alchemical processes and for several respected scientists and intellectuals until the early development of different experimental apparatus. In ancient eighteenth century. Some of the early renowned modern India, the chemical excellence in various aspects of alchemists include Jan Baptist van Helmont, Robert Boyle scientific developments was highly acclaimed and was far and .

344 SCIENCE AND CULTURE, NOVEMBER-DECEMBER, 2016 Early Chemistry of 17th and 18th Centuries formulated the concept of latent heat to explain the thermo- Roger in 1605 in his book, ‘The chemistry of phase changes. Proficiency and Advancement of Learning’, presented an In 1702, German chemist Georg Stahl assigned the outline of the scientific methods developed during the name ‘phlogiston’ to the substance believed to be released period. Michal Sedziwoj in his alchemical treatise, ‘A New in the process of burning. J. J. Beecher proposed that in Light of Alchemy’, in the same year, indicted the presence the process of burning of a substance, phlogiston is added of the ‘food of life’ in the air, later identified as oxygen. to the flame of the burning object from air, in some cases, Jean Beguin described the first-ever chemical equation in producing a product. The English chemist Henry his book, ‘Tyrocinium Chymicum’, in 1615. Rene Descartes Cavendish in 1766 discovered the colorless and odorless in 1637 presented a detailed description of the existing , hydrogen, as ‘inflammable air’ which burns and can scientific methods in his publication, ‘Discours de la form an explosive mixture with air. In 1774, the English method’. A group of chemists, namely, Robert Boyle, chemist Joseph Priestley isolated pure oxygen as and John Mayow, at Oxford being ‘dephlogisticated air’, the existence of which was indicated encouraged by the new concept of the empirical earlier in 1773 by the Swedish chemist Carl Wilhelm methods propounded by Bacon and others, began to reshape Scheele as ‘fire air’. Cavendish suggested that oxygen is a the old alchemical traditions into an organized scientific part of air that combines with substances as they burn. discipline of chemistry. Priestley is also credited for the discovery of soda water Robert Boyle (1627–1691) made a clear and several other ‘airs’ (). differentiation between the activities of alchemy and the In eighteenth century, the French chemist Antoine- scientific experimental approach towards matter initiating Laurent de Lavoisier through his pioneering research and the beginning of the history of modern chemistry. He development in chemistry established the subject on proper believed that the developed scientific methods denied the theoretical footings. He proposed that air is composed of limitation of chemical elements to only the four classical two parts, namely, oxygen (Greek for acid-former) which elements of Aristotle and put forward a mechanistic combines with metals to form calxes (powdery substance) alternative of atoms and chemical reactions that could be and the azote (Greek for no life). Lavoisier in his the subject of rigorous experiment. He suggested that all ‘Considérations Générales sur la Nature des Acides (1778)’ theories must be experimentally proved before being indicated that the ‘air’ responsible for combustion, was the accepted as true. His work was involved with some of the source of acidity and all acids contained oxygen. He also modern ideas of atoms, molecules and chemical reactions. demonstrated that the ‘inflammable air’ (hydrogen) He favored the word corpuscle as finest division of matter combined with the ‘dephlogisticated air’ (oxygen) to over atom. The book, ‘The Sceptical Chymist’, in which produce a dew appeared to be water. Mikhail Lomonosov he proposed the hypothesis that every phenomenon is the in Russia anticipated the kinetic theory of gases during the result of collisions of particles in motion acted as a period. landmark publication in the field of chemistry. He is however best known for his Boyle’s Law introduced in Lavoisier with Pierre-Simon Laplace in 1782-83 1662 describing the relationship between the pressure and introduced a technique for determination of the heat volume of a gas under different experimental conditions. involved in various chemical changes using an ice- Robert Boyle for his pioneering contributions in chemical calorimeter leading to the foundation of thermo-chemistry. science is regarded as the Founding Father of Modern In 1787, Lavoisier and Claude Louis Berthollet in their Chemistry. ‘Methods of Chemical Nomenclature’ described a new system of chemical nomenclature for the chemical During the period, it became evident that ‘air’ is compounds such as sulfuric acid, sulfates and sulfites still comprised of different gases. Jan Baptist van Helmont in use today. Lavoisier in his publication, ‘Traite coined the word ‘gas’ from the Greek word in Elementaire de Chimie (Elementary Treatise of Chemistry, naming some insubstantial substances present in the ‘air’ 1789)’, which is considered as the first modern chemical and is remembered today as the founder of pneumatic text book, presented a new theory as ‘Lavoisier’s Law’ chemistry. In 1754, Helmont along with Joseph Black elucidating the principle of conservation of mass. He discovered , called as ‘fixed air’. Helmont believed in the theory of radicals which functions as a in his work, Ortus medicinae, in 1648 proposed an early single group in a . He also indicated that version of the Law of conservation of mass. Black in 1758

VOL. 82, NOS. 11–12 345 diamond is a crystalline form of carbon. Lavoisier The English chemist John Dalton in 1803 described introduced the use of chemical balance in the laboratory. the relationship between the components in a mixture of gases and the relative pressure each contributes to that of Lavoisier through his fundamental scientific the overall mixture as Dalton’s law of partial pressures. contributions towards systematic chemical experimentations Dalton in his ‘New System of Chemical Philosophy (1808- and their quantitative way of presentation brought about a 1827)’ outlined the modern views on the atomic theory revolution in chemical science. He observed, “I have and suggested that all matters are composed of small tried...to arrive at the truth by linking up facts; to suppress indivisible ‘atoms’ and different atoms have different as much as possible the use of reasoning, which is often atomic weights and also stressed that the chemical elements an unreliable instrument which deceives us, in order to combine in integral ratios which is known as ‘Dalton’s Law follow as much as possible the torch of observation and of multiple proportions’. French chemist Joseph of experiment.” Lavoisier is celebrated as the ‘father of Proust in1804 proposed the ‘Law of definite proportions’ modern chemistry’ and a chemical analogue of Isaac which states that elements always combine in small and Newton in physics. whole number ratios to form compounds. The two laws, During the period, the elements, cobalt, nickel and the ‘Law of multiple proportions’ and the ‘Law of definite , were respectively identified by the Swedish proportions’, form the basis of the development of chemist Georg Brandt in 1735, Axel Fredrik Cronstedt in stoichiometry, the term introduced by J. Benjamin Richter. 1751 and Lose and Fausto Elhuyar in 1783. Axel Fredrik The English chemist Jons Jacob Berzelius in his Cronstedt is considered as one of the founders of modern publication, ‘Lärbok i Kemien’, in 1808 introduced the mineralogy. Louis Claude Cadet de Gassicourt synthesized classical system of chemical symbols and notation. The the first organometallic compound, namely, cacodyl oxide in elements were abbreviated by one or two letters, for 1757. Berthelot in 1785 produced the strong example, O for oxygen, Fe for iron, etc. and the elemental oxidant, potassium chlorate (KClO ), as Berthelot’s salt and 3 proportions in a compound were noted by numbers, the also determined the elemental composition of ammonia. same basic system used today. However, in presenting the He also introduced the theory of chemical equilibrium. formula of a compound, Berzelius used a superscript The Italian physicist Alessandro Volta in 1784 while number, e.g., H2O, instead of the subscript used today, e.g., investigating ‘animal electricity’ discovered by Luigi H2O. He also developed the theory of chemical Galvani utilizing frog leg as a detector devised an combination suggesting that reactions occur with stable electrochemical cell that derived electrical energy from groups of atoms called radicals. His work on precise spontaneous redox reaction taking place within the cell. determination of elementary constituents of large numbers Volta thus developed the electrochemical theory of chemical of compounds provided evidence in favor of Dalton’s combinations and became the founder of electrochemistry. atomic theory that inorganic chemical compounds are Michael Faraday through his studies on electro-deposition composed of atoms combined in whole number amounts. of metals associated with quantities of chemical elements Berzelius discovered the elements, silicon, selenium, during electrolysis, made a major contribution to thorium and cerium, and the elements, lithium and electrochemistry and provided important clues in elucidating vanadium, were identified by his associates. He tried to the atomic nature of matter. compile a table of the known elements on the basis of their relative atomic weights in 1828. He believed that salts th Chemistry of 19 Century to the Present are compounds of an acid and a base, and also indicated In 1801-1802, the French chemist Joseph Louis Gay- that the anions in acids would be attracted to a positive Lussac in his ‘Charles’s Law’ proposed that equal volumes electrode (the anode) and the cations in bases to a negative of all gases expand equally with the same increase in electrode (the cathode). He introduced the chemical terms, temperature. Later in 1808, Gay-Lussac deduced ‘Gay- catalysis, polymer, isomer and allotrope, although the Lussac’s Law’ or the ‘Law of Combining Volumes’ original definitions sometimes differ from modern usage. suggesting that gases at constant temperature and pressure Friedrich Wohler and the German chemist Justus von Liebig combine in simple numerical proportions by volume and in 1825 confirmed the concept of isomerism suggesting the resulting product or products bear a simple proportion that it is caused by differing in arrangements of the atoms by volume to the volumes of the reactants. Gay-Lussac within a molecular structure. Berzelius for his original along with Louis Jacques Thenard identified the element contributions in science of chemistry is known as the father boron through decomposition of boric acid. of modern chemistry along with Lavoisier and Boyle.

346 SCIENCE AND CULTURE, NOVEMBER-DECEMBER, 2016 The English chemist Humphrey Davy, as one of the effect of individual nutrients on crops, is considered as the pioneers in the field of electrolysis, discovered nine new ‘father of fertilizer industry’. elements including the alkali metals, sodium and potassium, Germain Hess in his law of conservation of energy, and the alkaline earth metals, magnesium, strontium and known as ‘Hess’s law’, in 1840 established that the barium. In 1810, he renamed the ‘dephlogisticated marine energy change in a chemical process depends on the states acid’, discovered earlier by Carl Wilhelm Scheele in 1774, of the starting and product materials only and not on the as the element, chlorine. Scheele also gave a hint for the specific reaction pathway between the two states. In 1864, formation of aqua regia and identified nitrous oxide known Cato Maximilian Guldberg and Peter Waage proposed the as laughing gas simply by inhaling. The French chemist ‘Law of mass action’. Louis Pasteur in 1849 suggested that Bernard Courtois discovered the element iodine in 1811. the racemic form of tartaric acid is a mixture of the In 1815, Davy invented the Davy lamp, which allowed the levorotatory and dextrorotatory forms, thus identifying the miners to work safely in the coal mines in presence of nature of optical rotation which led to the initiation of the flammable gases like methane but did not patent it for the field of stereochemistry. In 1873, Jacobus Henricus van’t benefit of the workers. Hoff and Joseph Ahille Le Bel independently developed The Italian physicist Amedeo Avogadro in his the model for chemical bonding and studied optical ‘Avogadro’s law’ in 1811 postulated that under control activity in chiral compounds. The concept of the conditions of temperature and pressure, equal volumes of ‘asymmetrical carbon atom’ provided an explanation for gases contain equal number of molecules. He also suggested the occurrence of numerous isomers. that simple gases are compound molecules of two or more William Thomson, better known as Lord Kelvin, in atoms and not of solitary atoms. In 1850s, several chemists 1848 introduced the concept of absolute zero, the like Alexander Williamson in England, Charles Gerhardt temperature at which all molecular motion ceases. In 1852, and Charles-Adolphe Wurtz in France and August Kekule in August Beer, on the basis of the work of Pierre Bouger , advocated for reformation of theoretical and Johann Heinrich, proposed the ‘Beer’s law’ which chemistry to make it consistent with Avogadro hypothesis. explains the relationship between the composition of a Stanislao Cannizzaro constructed a systematic theoretical mixture and the amount of light it absorbs leading to the structural concept that fit almost all of the available development of the important analytical technique of empirical evidences and suggested that most of the spectrophotometry. The technique of spectroscopy was elementary gases are diatomic, some are monatomic and a effectively utilized by Robert Bunsen and Gustav few are more complex. He also proposed a relation among equivalent weight, atomic weight and molecular weight on Kirchhoff (1859-60) to discover the elements, caesium and the basis of Avogadro’s hypothesis. Johann Josef rubidium, and the British chemist Crookes to identify Loschmidt in 1865 predicted the exact number of molecules thallium in some seleniferous deposits in 1861. in a mole, later named as Avogadro’s number. Benjamin Silliman Jr. in 1855 developed the methods The synthesis of the organic compounds, urea, by of petroleum cracking initiating research in the field of Friedrich Wöhler in 1828 and acetic acid by Hermann modern petrochemical industry. The refinement of Kolbe in 1847 completely from inorganic sources, helped petroleum extracted from earth provided a host of liquid in making an essential distinction between organic and fuels such as gasoline, diesel, solvents, lubricants, waxes inorganic substances in chemistry. In 1827, William and many other common materials of the modern world, Prout classified bio-molecules into their modern groupings such as synthetic fibers, plastics, paints, detergents, of carbohydrates, proteins and lipids. Wöhler and Justus pharmaceuticals, adhesives and ammonia as fertilizer. The von Liebig explained functional groups and radicals in preparation of the dye, mauveine or Perkin’s mauve, by relation to organic chemistry in 1832. By the end of the Sir William Henry Perkin in 1856 and that of indigo dye century, hundreds of organic compounds like synthetic dyes, by Adolf von Baeyer from coal tar in 1865, formed the drugs, etc. have been synthesized. Liebig, in addition to milestone for the synthesis of dyes in industrial organic his work in organic chemistry, also made major chemistry. Similarly, in 1862, Alexander Parks synthesized contributions to agricultural and biological chemistry. The a new synthetic polymer, Parkesine, leading to the German chemist Liebig for his contributions involving the foundation of the modern plastics industry. One of the first discovery of nitrogen as an essential plant nutrient and commercially available plastics, Bakelite, was invented by formulation of the ‘Law of the Minimum’ dealing with the Leo Baekeland during the period.

VOL. 82, NOS. 11–12 347 The German chemist August Kekule von Stradonitz later and each of which filled the assigned position in the in his book, Lehrbuch der organischen Chemie (Textbook periodic table. of Organic Chemistry), in 1859 indicated that tetravalent In 1894, Scottish chemist William Ramsay and Lord carbon atoms can link together to form a ‘carbon chain’ or Rayleigh discovered the monatomic and chemically inert a ‘carbon skeleton’, to which other atoms like hydrogen, gaseous element argon in air. In the following year, Ramsay oxygen, nitrogen and chlorine can be attached. In 1865, identified another inert gaseous element from cleveite Kekulé established the cyclic structure of benzene as a six mineral and named it as helium, the presence of which carbon ring with alternate single and double bonds and was indicated earlier in the solar spectrum. Ramsay and described the nature of the aromatic compounds based on the British chemist Morris W. Travers in 1898 isolated three benzene molecule. The Swedish chemist Alfred Nobel more inert gaseous elements, neon, krypton and xenon, prepared an explosive compound, nitroglycerin, from air. The discovery of the inert gases, later called as incorporated in a safer inert absorbent like kieselguhr noble gases, resulted in completion of the basic structure (diatomaceous earth) and patented as dynamite in 1867. of the periodic table. In designing the periodic table, the Nobel later developed a more powerful explosive than great visionary, Dmitri Mendeleev, as an icon in science dynamite, a transparent jelly-like substance, Gelignite or embodied the most fundamental principles lying at the core blasting gelatin, in 1876. of the subject of chemistry. In nineteenth century, several scientists in facilitating Antonius Van den Broek in 1911 suggested that the their studies in science felt the need to classify and elements would be more properly organized in the periodic systematically arrange the elements already discovered table if the elements were arranged on the basis of their during the period. In 1815, William Prout was the first to positive nuclear charges rather than that of their atomic propose for arrangement of the elements in order of their weights. In 1913, Henry Moseley following the work of atomic weights as the atomic weights of the known Broek introduced the concept of atomic number and elements were found to be the exact multiples of the atomic proposed that the properties of the elements are periodic weight of hydrogen. Johann Wolfgang Dobereiner in 1817 functions of their atomic numbers and not atomic weights tried to draw a relation between the atomic weights and as indicated by Mendeleev and others. Presently, to the properties of the elements through his concept of ‘triad’. identify the periodic trends, the chemical elements are Berzelius in 1828 compiled a table of relative atomic arranged in groups or columns and periods or rows weights of 43 known elements setting the weight of oxygen primarily based on the increasing orders of their atomic exactly equal to 100. In 1862, Beguyer de Chancourtois numbers in the periodic table. With wide acceptance, the tried to arrange the elements in the order of their ascending periodic law and the table have now become the basic atomic weights in a telluric helix form, a three-dimensional framework for a great part of chemical science. version of the periodic table. John A. R. Newlands in 1963- 65 devised the ‘law of octaves’ which was further modified American physicist J. Willard Gibbs in his study on by Luther Myer of Germany to organize the elements in a thermodynamic, introduced the concept of chemical periodic table in 1864. potential or the ‘fuel’ that makes chemical reactions to take place. In Gibbs’ phase rule, he included almost all the The Russian chemist Dmitri Mendeleev made a variables like temperature, pressure, energy, volume and breakthrough in devising a systematic periodic classification entropy generally involved in a chemical reaction. In of the 66 known chemical elements in the ascending order 1884, van’t Hoff proposed a general thermo-dynamical of their atomic weights in the modern form of the Periodic relationship between the heat of conversion and the Table. The periodic table published in his Principles of displacement of equilibrium as a result of temperature Chemistry in 1869, displayed a recurring pattern or variation in chemical kinetics. The concept of this mobile periodicity of properties within groups of the known equilibrium was subsequently modified by Henry Louis Le elements. In the later version of his periodic table published Chatelier in 1885 through the ‘van’t Hoff-Le Chatelier in 1871, he confidently predicted the positions and the principle’ or simply ‘Le Chatelier’s principle’. The likely properties of three yet-to-be-discovered elements, application of thermodynamics to chemistry by Gibbs and designated as eka-boron (Eb), eka-aluminum (Ea) and eka- others was instrumental in transforming physical silicon (Es). The predictions for the yet-to-be discovered chemistry into an important branch of deductive science in elements were proved to be the properties of the elements, chemistry. scandium, gallium and germanium, respectively discovered

348 SCIENCE AND CULTURE, NOVEMBER-DECEMBER, 2016 Hermann Emil Fischer (1884-86) studied the is absorbed or emitted when an electron moves from one chemistry of glucose and related sugar and also synthesized orbit to another producing a characteristic emission and proposed the structure of purine, a key structure in spectrum for the element. Frederick Soddy introduced the different bio-molecules. Alfred Werner through his work concept of isotopes in 1913 and also discovered the element on the octahedral structure of cobalt complexes established protactinium in 1917. the field of co-ordination chemistry in 1893. Rutherford in 1919 reported the discovery of In the last decade of the nineteenth century, several artificially induced nuclear transmutation, the dream of the landmark discoveries on the sub-atomic particles and the earlier alchemists, through a nuclear reaction between atomic structure encouraged the scientists in initiating a nitrogen atoms and alpha particles producing oxygen atoms new field of research in Nuclear Science. J. J. Thomson in and protons, represented as 14N(α, p)17O. During the period, 1897 discovered the negatively charged particle, electron, different advanced nuclear devices like the cyclotron the first particle to be recognized as a constituent of all conceived by E. O, Lawrence in 1929 and the electrostatic atoms using the cathode ray tube. Eugene Goldstein in 1886 accelerator built by Cockcroft and Walton in 1932 for and Wilhelm Wien in 1898 predicted the existence of the accelerating nuclear particles as projectiles to cause nuclear positively charged particle as canal rays or positive rays transmutation were invented. Irene Curie-Joliot and her (streams of positive ions) with a charge equal and opposite husband Frederic Joliot in 1934 demonstrated that to the negatively charged electron and Rutherford in 1920 radioactive elements could be created artificially in the suggested the name, proton, for this positively charged laboratory. The German scientist Otto Hahn along with his particle. The electrically neutral nuclear particle, neutron, coworkers in 1939 discovered the neutron induced nuclear was however, discovered later by James Chadwick in 1932. fission resulting in release of a large amount of nuclear Studies on canal rays by Wien in 1898 led to energy. In USA, the Manhattan Project was in process at the development of the important analytical technique of the University of Chicago and the very first nuclear fission mass spectrometry. reactor was developed under the leadership of Enrico Fermi in 1940. The important discoveries and outstanding During the period, Wilhelm Conrad Roentgen while achievements in nuclear science since the last decade of working on the effect of cathode rays on barium the nineteenth century, in general, resulted in the platinocyanide, discovered X-rays in 1895. Similarly, in development of a new branch of chemistry in chemical 1896, Henri Becquerel in his studies on fluorescence with science, namely, nuclear chemistry. potassium uranyl sulfate observed that the salt emits a fluorescent light with or without the aid of sunlight and he In the beginning of the twentieth century, the termed it as ‘Becquerel Rays’ or ‘Uranic Rays”. Thus, the American scientists Linus Pauling and Gilbert N Lewis phenomenon of radioactivity was discovered and the term established the electronic theory of chemical bonds and ‘radioactivity’ was first used by Polish-born Marie molecular orbital, known as ‘valence bond theory’. In 1902, Sk³odowska Curie. Marie Curie along with her husband, Lewis suggested that the chemical bonds are formed French physicist Pierre Curie in 1898 discovered two new through the transference of electrons in the outermost radioactive elements, radium and polonium, in pitchblende ‘valence’ shell of the atom, to give each atom a complete mineral through their nuclear properties of radioactivity. set of eight outer electrons (an ‘octet’). In the article ‘The Atom of the Molecule’ in 1916, he indicated that a chemical Earnest Rutherford in 1906 developed an atomic bond is formed by a pair of electrons shared by two atoms model, known as ‘Rutherford model’, which was later and also introduced the ‘electron dot diagrams’ to symbolize modified by Danish physicist Niels Bohr and Henry the electronic structures of atoms and molecules, now Moseley. In 1911, Rutherford while studying the known as ‘Lewis structures’. Subsequently, American characteristic properties of radioactivity, discovered three chemist Irving Langmuir in1919 introduced the term types of radiations, namely, alpha particles (α, positively covalent bond. In 1920s, the Lewis’s model of the electron- charged), beta particles (β, negatively charged) and gamma pair bond was effectively applied by the British chemists rays (γ, neutral electromagnetic radiation) and also Arthur Lapworth, Robert Robinson, Thomas Lowry and demonstrated that atoms of one radioactive element would Christopher Ingold in organic chemistry and the American spontaneously turn into atoms of another element with chemist Maurice Huggins and the British chemist Nevil emission of radiation. Bohr in 1913 introduced the concept Sidgwick in coordination chemistry. In 1912, Peter of quantum mechanics to atomic structure through his ‘Bohr Debye developed the concept of molecular dipole to model’. He also postulated that electromagnetic radiation

VOL. 82, NOS. 11–12 349 describe asymmetric charge distribution in some molecules. considered as the milestones in the history of quantum In 1923, Lewis and M. Randall published ‘Thermodynamics chemistry. and the Free Energy of Chemical Substances’, the first In 1953, the heuristic approach of James Watson and modern treatise on chemical thermodynamics. Francis Crick in deducing the double helical structure of Lewis developed the electron pair theory of acids and DNA capable of explaining by the knowledge of chemistry bases in which an acid as any atom or molecule with an and the X-ray diffraction patterns, led to an explosion of incomplete octet is capable of accepting electrons from research in the field of biochemistry. The development of another atom and a base is, of course, an electron donor. the method of polymerase chain reaction (PCR) by Kary In 1909, S. P. L. Sorensen developed the concept of pH in Mullis in 1983 for in-vitro amplification of DNA in the measuring acidity. Svante Arrhenius in his acid-base theory laboratory has made possible the study of sequence of DNA stated that an acid is a substance that produces hydronium of organisms culminating in the growth of the human ion when it is dissolved in water and a base is one that genome project. Miller-Urey demonstrated that the basic produces hydroxide ion in water. Acidity based on constituents of proteins and amino acids could themselves Brønsted–Lowry definition was expressed as the acid be built up from simpler molecules in a simulation of primordial processes on earth and this was perhaps the first dissociation constant (Ka) which measures the relative ability of a substance to act as an acid. attempt by chemists to study hypothetical processes of the origin of life in the laboratory under controlled conditions. The important analytical technique, chromatography, was invented by Mikhail Tsvet in 1903. The development Harold Kroto, Robert Curl and Richard Smalley in of the Haber or Haber-Bosch process by Fritz Haber and 1985 discovered fullerenes, a class of large carbon Carl Bosch in 1905 for preparation of ammonia through molecules, superficially resembling the geodesic dome. The combination of nitrogen and hydrogen has become an carbon nanotube, a cylindrical type of fullerene, invented important landmark in industrial chemistry with deep through electron microscopy by Sumio Lijima in 1991, is consequences in agricultural production of fertilizers and being used as an important component in the field of munitions. Haber has been considered as the ‘father of nanotechnology. In 1970, John Pople developed the chemical warfare’ for his work on deploying chlorine and Gaussian program suitably applied to computational other poisonous gases during World War I. In 1912, chemistry. Eric Cornell and Carl Wieman in 1995 produced William Henry Bragg and William Lawrence the first Bose-Einstein condensate, a substance that displays quantum mechanical properties on the macroscopic scale. Bragg proposed ‘Bragg’s law’ and developed the technique of X-ray crystallography, effectively utilized as a tool in In mid-twentieth century, chemical investigations on elucidating the crystal structure of substances. the quality and purity of the intrinsic semiconductor materials like single crystals of silicon and germanium and In 1924, the French quantum physicist Louis de their chemical compositions when doped with other Broglie introduced the theory of electron waves based on elements, made possible the production of the solid state ‘wave-particle duality’ in which he proposed that particles transistors and other precise electronic devices, especially can behave like waves and waves (radiation) can behave computers in the later stage of its scientific advancements. like particles. In 1926, Austrian physicist Erwin Schrödinger on the basis of the wave-particle duality theory Since 1950s, several important discoveries in nuclear introduced a wave equation, known as the Schrodinger science have resulted in the synthesis of the heavy and equation. Austrian-born physicist Wolfgang Pauli in 1925 super-heavy elements beyond uranium with sufficient through his ‘Pauli Exclusion Principle’ which states that stability enabling to study their properties in conformity no two electrons around a single nucleus in an atom can with periodic law of the periodic table. American nuclear occupy the same quantum state simultaneously, made major chemist G. T. Seaborg along with others is best known for contributions to the development of the quantum mechanics the discovery and isolation of the trans-uranium elements. and quantum field theory. German physicist Werner The chemical element, Seaborgium (element 106), was Heisenberg in formulating quantum mechanics in terms of named in his honor during his life time like that of the matrices introduced his ‘uncertainty principle’ regarding the chemical element, Einsteinium (element 99), named to status of an electron in an atom in 1927. Studies on the honor Albert Einstein. Currently, several groups of nuclear application of quantum mechanics to the diatomic scientists have been engaged in successful synthesis of the hydrogen molecule and the phenomenon of the chemical super-heavy elements in different advanced nuclear research bond by Walter Heitler and Fritz London in 1927 are often laboratories in USA, USSR, France and Germany and the

350 SCIENCE AND CULTURE, NOVEMBER-DECEMBER, 2016 latest evidence of their endeavor is the production and primarily confined to simple observations on the natural characterization of the super-heavy element, Z-117, through materials under the environmental conditions of the nuclear reaction, 249Bk(48Ca, 3-4n)293,294Z-117, in GSI, temperature, pressure and exposition to natural solar Germany, also reported earlier by a Group of Russian radiations on Earth. Gradually, the rational reasoning on scientists in 2010. the existences of the surrounding matters in different phases In the earlier period, the chemists in general were started with the acceptance of the fundamental concepts very much reluctant in the application of mathematics in and laws time to time introduced in the development of chemistry. Auguste Comte in 1830 made the comment, modern chemistry. In the beginning, however, the matters “Every attempt to employ mathematical methods in the within the atomic nuclei or the nuclear phenomenon were study of chemical questions must be considered profoundly disregarded. With the advancement of science, the subject irrational and contrary to the spirit of chemistry”. However, of chemistry has been re-defined as the science of matter in the later part of the nineteenth century, the conception dealing with the composition and structural properties of has gradually been changed, for example, August substances and their transformations under different Kekule wrote “I rather expect that we shall someday find conditions, both natural and artificial. a mathematico-mechanical explanation for what we now Discovery of radioactivity, the sub-atomic particles call atoms which will render an account of their and studies on the atomic structure in the later period of properties’’. With rapid progress and outstanding modern chemistry encouraged the scientists to rethink about development in chemical research, the activities of the characteristic properties of matter. Studies on matters chemistry have now become intermingled with almost all in their atomic, molecular or aggregate scale, including the major branches of science resulting in extensive effects of interactions (bombardment) of fundamental advancement of science in general. particles like proton, neutron or heavy ions with matter are now formally recognized as essential subjects of Disciplines of Chemistry investigation in chemistry. Presently, the advanced areas In practice, the subject of chemistry is now of chemical science like quantum chemistry, nuclear traditionally grouped into several major sub-disciplines chemistry and many others have been extensively developed based on the type or kind of matter being investigated, and formally accepted as important sub-fields of study in although there are several cross-disciplinary and more chemistry. Nevertheless, the field of chemistry is very broad specialized fields in chemical science. Some of the major and is sometimes considered as the central science as it sub-disciplines of chemistry are – Analytical chemistry bridges many other major branches of science and hence (deals with chemical composition and structure of sample the claim that chemistry is everywhere is found to be true materials), Biochemistry (deals with substances of biological and justified. organisms), Inorganic chemistry (deals with inorganic matters), Nuclear chemistry (deals with sub-atomic nuclear Appendix particles and transmutations), Organic chemistry (deals with Scientists engaged in studies in chemical science are carbon based matters), Physical chemistry (deals with the generally designated as chemists and the subject involved chemical processes involving physical concepts such as is known as chemistry. Some essential concepts of study thermodynamics, quantum mechanics, etc.) and others. in chemistry are atom, element, molecule, compound, ion, In addition, many more specialized fields such as bonding, energy, etc. Matter can exist in several phases Agro-chemistry, Atmospheric chemistry, Chemical biology, and can be studied in isolation or in combination. The most Cosmo-chemistry, Electrochemistry, Environmental familiar phases are solid, liquid and gaseous and the less chemistry, Geo-chemistry, Green chemistry, Marine familiar phases include plasmas, Bose-Einstein condensates chemistry, Material science, Nanotechnology, Natural and fermionic condensates, and paramagnetic and product chemistry, Petro-chemistry, Pharmacology, Photo- ferromagnetic phases of magnetic materials. chemistry, Polymer chemistry and many others, have been emerged in recent years with rapid advancement in According to the International Union of Pure and chemical sciences. Applied Chemistry (IUPAC) gold book, a chemical reaction is ‘a process that results in the inter-conversion of chemical Conclusion species’. A chemical reaction can be depicted symbolically through chemical equation. The number of atoms on the Studies in chemistry, in early civilizations, were

VOL. 82, NOS. 11–12 351 left and the right sides of a chemical reaction for chemical 2011 was declared by the United Nations as the transformation is equal but when unequal, the International Year of Chemistry. transformation by definition is not chemical, but rather a The present article is primarily based on the (i) nuclear reaction or a radioactive decay process. The History of Chemistry, Wikipedia, the free encyclopedia and standard nomenclature of a chemical compound is set by (ii) Chemistry, Wikipedia, the free encyclopedia, retrieved the IUPAC. The Chemical Abstracts Service has devised a on 23. 09. 2015. To have detailed information, further method to index chemical substances. In the initiative of readings of the cited Wikipedia along with the referred the IUPAC and of the United Nations Educational, references and other relevant communications are Scientific, and Cultural Organization (UNESCO), the year needed. S

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