Chemistry

I. Introduction

Chemistry is the science of molecules, or more precisely the science of the chemical structure of molecules in relation to their properties. At the same time, chemistry is concerned with the study of transformation, of the material metamorphosis of materials. Notably, when Christian missionaries first began to translate western textbooks into Chinese in the 1870s and needed a term to stand for chemistry, they coined the phrase ʺhua-hsüehʺ, literally meaning ʺthe study of change.ʺ The chemical approach to the interpretation of the material world has the unique and fascinating characteristic of linking the macroscopic world, the properties of all that surrounds us with the phenomena that happen inside and outside us, to the microscopic world of molecules and atoms. Chemistry is fascinating for its infinite possibilities and the vast horizons of creativity that it opens up. It is unique for its investigative capacity and its knowledge is indispensable for the pursuit of any of the other sciences. Today chemistry has become an incredibly rich and powerful science and often its areas of investigation overlap with that of physics and biology. The study of modern chemistry has branched out into several sub-disciplines such as physical chemistry, organic chemistry, inorganic chemistry, analytical chemistry and biochemistry.

II. A Brief History of Chemistry

1. Roots in the Ancient World. Ancient civilizations had knowledge of seven metals (gold, silver, copper, lead, tin, iron and mercury) and a wide variety of chemicals that they exploited in their pottery, jewellery, cosmetics, cooking and weaponry or as drugs. The very first appearance of chemistry could be traced as back as the Stone Age. The Palaeolithic (Old Stone Age) paintings at Lascaux and elsewhere show that stone-age people were able not merely to alter stones to fashion tools and buildings but also to prepare pigments to colour their representations of animals (12,000-8,000 B.C.). By the time the bronze or copper age was reached, the working of minerals to produce copper and zinc had been developed. These metallurgical practices continued with the discovery of iron ore, which gave iron-age man to produce weapons that made animal hunting and butchering easier. Around 300,000 years ago men had learned how to create, control and propagate fire, providing humans with warmth, expanding their daylight hours and improving diet, health and longevity through the processing of meat and vegetables. There is abundant archaeological evidence that by 8,000 B.C. humankind was using biochemical processes (fermentation) to exploit grains of various kinds to bake bread and create beer and wine. The ability to control fire and temperature led to the first chemical technologies such as the production of pottery, metals, glass and bitumen products.

The earliest critical thinking on the nature of substances was by Greek philosophers beginning about 600 B.C. Thales of Miletus, Anaximander, Empedocles, and others propounded theories that the world consisted of varieties of earth, water, air, fire, or indeterminate “seeds” and “unbounded” matter. Leucippus and Democritus propounded a materialistic theory of invisibly tiny irreducible atoms from which the world was made. In the 4th century B.C., Plato taught that the world of the senses was but the shadow of a mathematical world of “forms” beyond human perception. In contrast, Plato’s student Aristotle took the world of the senses seriously. Adopting Empedocles’s view that everything is composed of earth, water, air, and fire, Aristotle taught that each of these materials was a combination of qualities such as hot, cold, moist, and dry. For Aristotle, these “elements” were not building blocks of matter as we think today; rather, they resulted from the qualities imposed on otherwise featureless prime matter. Consequently, there were many different kinds of earth, for instance, and nothing precluded one element from being transformed into another by appropriate adjustment of its qualities. Thus, Aristotle rejected the speculations of the ancient atomists and their irreducible fundamental particles. His views were highly regarded in late antiquity and remained influential throughout the Middle Ages.

For thousands of years before Aristotle, metalsmiths, assayers, ceramists, and dyers had worked to perfect their crafts using empirically derived knowledge of chemical processes. By Hellenistic and Roman times, their skills were well advanced, and sophisticated ceramics, glasses, dyes, drugs, steels, bronze, brass, alloys of gold and silver, foodstuffs, and many other chemical products were traded. Hellenistic Alexandria in Egypt was a centre for these arts, and it was apparently there that a group of ideas emerged that later became known as alchemy.

2. Alchemy. In early times, chemistry was more an art than a science. The first forms of ʺchemicalʺ were linked to the discovery of the properties of minerals and plants. Investigation of metals, plants and animals, revolved around the preparation of dyes, pigments, cosmetics and drugs, and were used empirically by ancient man to satisfying their needs and their sense of curiosity about the world they lived in. This body of knowledge about the transformations of matter is known as “alchemy” and it had often-mystical overtones.

The word alchemy was most probably derived from the Arabic word ʺalkimiaʺand may ultimately derive from the ancient Egyptian word ʺkmtʺ or ʺchem,ʺ meaning black or from the Greek ʺchyma,ʺ meaning to fuse or cast a metal.The operations of craftsmen were often carried out to the accompaniment of religious or magical practices, and supposed connexions were seen between metals, minerals, plants, planets, the sun, the moon, and the gods. The alchemist, through his work of transformation of matter, saw himself on a mystical path of personal elevation to the Transcendent involving at the same time the social and the ethical dimension in a process of purification of the self in order to be more available to higher ideals. Alchemy is of a twofold nature, an outward or ʺexotericʺ and a hidden or ʺesoteric.ʺ Exoteric alchemy is concerned with attempts to prepare a substance, the philosophers’ stone, or simply the Stone, endowed with the power of transmuting the base metals lead, tin, copper, iron, and mercury into the precious metals gold and silver. The Stone was also sometimes known as the Elixir or Tincture, and was credited not only with the power of transmutation but with that of prolonging human life indefinitely. The belief that it could be obtained only by divine grace and favour led to the development of esoteric or mystical alchemy, and this gradually developed into a devotional system where the mundane transmutation of metals became merely symbolic of the transformation of sinful man into a perfect being through prayer and submission to the will of God. The two kinds of alchemy were often inextricably mixed; however, in some of the mystical treatises it is clear that the authors are not concerned with material substances but are employing the language of exoteric alchemy for the sole purpose of expressing theological, philosophical, or mystical beliefs and aspirations. Many clerics were alchemists. To Albertus Magnus, a prominent Dominican and Bishop of Ratisbon, is attributed the work "De Alchimia", though this is of doubtful authenticity. Several treatises on alchemy are attributed to St. Thomas Aquinas. He investigated theologically the question of whether gold produced by alchemy could be sold as real gold, and decided that it could, if it really possess the properties of gold (Summa Theologiæ II-II, q. 77, a. 2). A treatise on the subject is attributed to Pope John XXII, who is also the author of a Bull Spondent quas non exhibent (1317) against dishonest alchemists.

3. The Development of Chemistry in the Islamic World. In the 7^th century, the Arabs started a process of territorial expansion that quickly brought their empire and influence ranging from India to Andalusia. Fruitful contacts with ancient cultural traditions were a natural consequence of this territorial expansion, and Arabic culture proved ready to absorb and reinterpret much of the technical and theoretical innovations of previous civilizations. This was certainly the case with respect to alchemy, which had been practiced and studied in ancient Greece and Hellenistic Egypt.  Alchemy came to the Muslims originally from Alexandria. Islam gradually appropriated the Greek alchemical authority in toto. The transmission was made chiefly through direct contact in Alexandria and other Egyptian cities. Nestorian Christians played a great part in translating Greek works into Arabic. The first Muslim to take an interest in alchemy was probably Khalid ibn Yazid (?-704) who seems to have first ordered the translation of alchemical books from the Greek and Coptic languages into Arabic. By the second part of the 8^th century, Arabic knowledge of alchemy was already far enough advanced to produce the Corpus Jabirianum—an impressively large body of alchemical works attributed to Jabir ibn Hayyan (c.721–c.815) also known in the West as Geber. The Corpus, together with the alchemical works of Muhammad ibn Zakariyā Rāzī (865–925), marks the creative peak of Arabic alchemy. The success of Arabic alchemy relied most certainly from the multicultural milieu of Hellenistic Egypt and included a mixture of local, Hebrew, Christian, Gnostic, ancient Greek, Indian, and Mesopotamian influences.

The contribution of Arabic alchemists to the history of alchemy is profound. They excelled in the field of practical laboratory experience and offered the first descriptions of some of the substances still used in modern chemistry. Muriatic (hydrochloric) acid, sulfuric acid, and nitric acid are discoveries of Arabic alchemists, as are soda (al-natrun) and potassium (al-qali). The words used in Arabic alchemical books have left a deep mark on the language of chemistry: besides the word alchemy itself, we see Arabic influence in alcohol (al-kohl), elixir (al-iksir), and alembic (al-inbiq). Moreover, Arabic alchemists perfected the process of distillation, equipping their distilling apparatuses with thermometers in order to better regulate the heating during alchemical operations. Finally, the discovery of the solvent later known as aqua regia—a mixture of nitric and muriatic acids—is reported to be one of their most important contributions to later alchemy and chemistry.

After the Middle Ages, among the most important of the European alchemists was German-Swiss physician Paracelsus (1493-1531). He expanded on the Arabic doctrine that two principles, sulphur and mercury, were the roots of all things by adding a third principle, salt. Paracelsus also taught that the universe itself functioned like a cosmic chemical laboratory. God the Creator, he believed, was a divine alchemist whose macrocosmic drama was mirrored in the microcosmic world of man and earthly creatures. It followed that physiological and pathological processes were chemical in nature, and that disease was best treated by chemical medicines rather than by the herbal ones of the ancients. Paracelsus practiced alchemy, Kabbala, astrology, and magic, and in the first half of the 16^th century, he championed the role of mineral rather than herbal remedies. His emphasis on chemicals in pharmacy and medicine was influential on later figures, and lively controversies over the Paracelsian approach raged around the turn of the 17^th century. It is worth noting that that open-minded empirical investigation well integrated with theory (which is how one might define science today) was not absent from the history of alchemy. Alchemy had many quite scientific practitioners through the centuries, notably including Britain’s Robert Boyle and Isaac Newton who applied systematic and quantitative method to their (mostly secret) alchemical studies. Indeed, as late as the end of the 17^th century, there was little to distinguish alchemy from chemistry, either substantively or semantically, since both words were applied to the same set of ideas. It was only in the early 18^th century that chemists agreed upon different definitions on the two words, forever discrediting alchemy as pseudoscience.

4. The Chemical Revolution. It was through the contribution of Robert Boyle (1627-1691) that a revolution started to take place in chemistry as it had already begun in physics with Galileo Galilei (1564-1642).  Central to Boyle’s contribution was his corpuscularian hypothesis. According to Boyle, all matter consisted of varying arrangements of identical corpuscles. In his 1661 book ʺThe Sceptical Chymist,ʺ Boyle explains his hypothesis and dismisses Aristotle’s four-elements theory, which had persisted through the ages. Boyle recognised that certain substances decompose into other substances (water decomposes into hydrogen and oxygen when it is electrically charged) that cannot themselves be broken down any further. These fundamental substances he labelled ʺelements,ʺ which could be identified by experimentation. By the late 18^th century, the field of chemistry had fully separated from traditional alchemy while remaining focused on questions relating to the composition of matter. The chemist who transformed our understanding about elements and composition was Antonie Lavoisier (1743-1794). In 1789, Lavoisier wrote the first comprehensive chemistry textbook, and, together with Robert Boyle, he is often referred to as the father of modern chemistry. Lavoisier compiled a list of metallic and non-metallic elements that would point towards the periodic table developed later by Mendeleev in 1869. The chemical revolution was not merely conceptual but also instrumental, in that it involved the practical ability to manipulate, weigh, and measure gases using accurate balances, glass apparatus etc… Around the turn of the 18^th century, the English Quaker John Dalton (1766-1844) began to wonder about the invisibly small ultimate particles of which each of these elemental substances might be composed. He thought that if the atoms of each of the elements were distinct, they must be characterised by a distinct weight that is unique to each element. Dalton’s atomic theory was a landmark event in the history of chemistry. Subsequently, in 1869, Mendeleev proposed a way to organise the sixty or so known elements at the time highlighting the periodic law. When elements are arranged according to the magnitude of their atomic weights in fact, they display a step-like alteration in their properties such that chemically analogues like the alkali metals (lithium, sodium, potassium, etc…) and the halogens (fluorine, chlorine, bromine, iodine) fall into natural groups. The turn of the 20^th century was marked by a remarkable series of discoveries that gradually shed light on the structure of the atom. J.J. Thomson (1856-1940) first proved that atoms were not the most basic form of matter. He demonstrated that all atom had fundamental particles with a net negative charge that, in his apparatus, could be deflected by magnetic or electric fields. There particles are now called electrons and are most relevant in chemistry. Subsequently, Robert Millikan (1868-1953) calculated the charge and the mass of a single electron. Shortly after Thomson’s discovery, Ernest Rutherford (1871-1937) with his famous experiment in which he collided α particles on a thin gold foil showed that both the mass and the charge of the atom were concentrated in a tiny fraction of its volume, the nucleus. He called these positive particles protons. Niels Bohr (1885-1962) developed Rutherford’s atomic model proposing that electrons moved around the nucleus in fixed circular orbits. In 1926 Erwin Schrödinger (1887-1961) took Bohr’s model one step further using mathematical equations to describe the likelihood of finding an electron in a certain position. In the current model of the atom, electrons occupy regions of space called ʺorbitalsʺ around the nucleus distributed according to a set of principles described by quantum mechanics. Linus Carl Pauling (1901–1994) made a significant contribution to the understanding of how atoms come together to form chemical bonding and chemical structure. He conducted pioneering studies in the magnetic properties of atoms and molecules and the relation of electronegativity (the tendency of an atom to attract electrons in a bond) to the types of bonds that atoms form To better explain the nature of covalent bonding, in which electrons are shared between bonded atoms, Pauling formulated the groundbreaking concepts of resonance and hybridization, which in turn provided chemists with a more robust theoretical basis for predicting new compounds and chemical reactions.

5. The Development of Organic Chemistry. At the beginning of the 19^th century, the elements and compounds known to chemistry numbered only a few hundred; today, they number more than seventy-one million. Few of these substances actually exist in Nature; rather they have been isolated, prepared, and studied by chemists in particular times and places by an evolving repertoire of laboratory practices and the development of organic chemistry. Prior to the 19^th century, chemists generally believed that organic compounds found in living organisms were too complex to be synthesised and studied. During this period, the concept of vitalism was widely accepted, according to which living organisms are fundamentally different from non-living entities or are governed by principles different from those at work in inanimate things. They also believed that all organic compounds possessed vital force, unlike inorganic. In 1828, Friedrich Wöhler (1800-1882) synthesised the organic compound urea from inorganic compounds ammonium cyanate challenging the idea of vitalism. Three decades after, the German chemist Friedrich August Kekulé (1829-1896) made a crucial contribution towards the birth of the new discipline by defining organic chemistry as the chemistry of carbon compounds, and by proposing not only that carbon atoms were tetravalent but also that they could bond to each other to form chains, comprising a molecular “skeleton” to which other atoms could cling. Kekule’s theory of chemical structure clarified the compositions of hundreds of organic compounds and served as a guide to the synthesis of thousands more. The history of organic chemistry continued with the discovery of petroleum and its separation into fractions according to boiling ranges, which lead to the petrochemical industry and later to the production of plastics. In the late 19^th century, the pharmaceutical industry began with the synthesis of acetylsalicylic acid (aspirin). The great organic synthesis that followed deeply revolutionized chemistry and society. The imitation of nature led to the possibility of breaking with nature itself and surpassing it to form an artificial world.

6. The Molecules of Life. From late 19^th century up until the First World War, the focus of the chemical research shifted significantly towards the studies and understanding of the chemistry underpinning the biological systems, thus leading to the birth of biochemistry. Biochemistry began with studies of substances derived from plants and animals with their classification into groups of biomolecules such as proteins, lipids, and carbohydrates. The German chemist Emil Fischer (1852-1919) in particular made a massive contribution by determining the nature and structure of many carbohydrates and proteins. By the end of the century, the role of enzymes as organic catalysts was clarified, and amino acids identified as constituents of proteins. The announcement of the discovery of vitamins ın 1912, independently by the Polish-born American biochemist Casimir Funk (1884-1967) and the British biochemist Frederick Hopkins (1861-1947), initiated a revolution in both biochemistry and human nutrition. Gradually, the details of intermediary metabolism, as well as the way the body uses nutrient substances for energy, growth, and tissue repair were unveiled. Perhaps the most representative example of this kind of work was the German-born British biochemist Hans Krebs (1900-1981) who established of the tricarboxylic acid cycle, also known as Krebs cycle, in the 1930s.

The most dramatic discovery in the history of 20^th century biochemistry however was surely the discovery of the double helix structure of DNA (deoxyribonucleic acid) in 1953 by American geneticist James Watson (1928- ) and British biophysicist Francis Crick (1916-2004) in 1953. Rosalind Franklin (1920-1958) also made a great contribution to the discovery of the molecular structure of the DNA. The new understanding of the molecule that encode the genetic code, the sequence of the four nucleotides adenine, guanine, cytosine, and thymine) provided an essential link between chemistry and biology. In June 2000, representatives from the publicly funded U.S. Human Genome Project and from privately held company Celera Genomics, simultaneously announced the independent and nearly complete sequencing of the more than three billion nucleotides in the human genome. However, both groups emphasized that this monumental accomplishment was, in a broader perspective, only the end of a race to the starting line.

7. The Future of Chemistry. In the 19^th century, the different scientific disciplines, including chemistry, came to have distinctive boundaries with their own academic journals and professional societies. However, we have now reached the stage in the 21^st century when cultural historians are asking whether it any longer makes sense to speak of chemistry as a separate discipline, because of the strong collaborative character of research involving mathematicians, physicists, biologists and engineers. So, what does the future of chemistry look like? Over the last two decades, innovation has mostly arisen at the boundaries of traditional subjects. Interdisciplinarity has become essential in tackling major technological and societal challenges and more in general a key factor in driving innovation. The chemical sciences will likely be increasingly required to solve challenges in health, energy and climate change, water and food production. One of the most important trends is the relationship of chemistry to biology and their role in shaping the pharmaceutical industry. Engagement with the arts and social sciences might also play a key role in changing attitudes to design and consumption, with implications for future manufacturing processes and use of natural resources. A decisive shift from blue-skies to problem-driven research seems to be marking the future of the chemical sciences.

III. Chemistry and Society

1. Chemistry and War. The Great War of 1914-1918 was the first conflict in which European chemists were involved in both defensive and offensive research to the point that is popularly known as ʺthe chemists’ warʺ because of the use of poisonous gas warfare such as tear gas and lethal agents like phosgene, chlorine, and mustard gas. By analogy, the second world conflict (1939-1945) has been called ʺthe physicists’ warʺ because of the research effort around the making of the atomic bomb. In fact, chemists were closely involved also in the second World War in the separation of uranium isotopes and in the manufacture of heavy water without which there would have been no such bomb.

In both world wars the chemical industry was dominated by the drive to improve and raise production levels of conventional high explosives and metal production for cannon. The petroleum soap (napalm) devised by Louis Fieser (1899-1977) killed more Japanese than the atomic weapons that destroyed Hiroshima and Nagasaki combined. Its use during the Korean War (1950-1953) and the prolonged Vietnam war (1955-1975) became a symbol of the evil of warfare and was responsible for a chemiophobic swing against chemistry that has had a lasting effect on popular culture.

For centuries weapons worked fuelled by gunpowder. The situation drastically changed when Alfred Nobel (1833-1896) invented dynamite in 1867, a substance easier and safer to handle than the less stable nitroglycerin, which had been discovered by Ascanio Sobrero (1812-1888) in 1847. Nitrogen plays a central role in the manufacture of explosives. In 1908, Fritz Haber (1868-1934) filed a patent on the ʺsynthesis of ammonia from its elementsʺ for which he was later awarded the 1918 Nobel Prize in Chemistry. Through this reaction, which today is known as the ʺHaber–Bosch process,ʺ ammonia, a chemically reactive, highly usable form of nitrogen, could be synthesized by reacting atmospheric nitrogen with hydrogen in the presence of iron at high pressures and temperatures. The importance of Haber’s discovery cannot be overestimated — as a result, millions of people have died in armed conflicts over the past 100 years, but, at the same time, billions of people have been fed. In his Nobel lecture, Haber explained that his main motivation for synthesizing ammonia from its elements was the growing demand for food, and the concomitant need to replace the nitrogen lost from fields owing to the harvesting of crops. In addition, the large-scale production of ammonia has facilitated the industrial manufacture of a large number of chemical compounds and many synthetic products. Thus the Haber–Bosch process, with its impacts on agriculture, industry and the course of modern history, has literally changed the world. What Fritz Haber could not foresee, however, was the environmental impact of his discovery, including the increase in water and air pollution, the perturbation of greenhouse gas levels and the loss of biodiversity that was to result from the colossal increase in ammonia production and use that was to ensue. The invention boosted the production of fixed nitrogen meeting the ever growing request of fertilizers as well as that of raw material for explosives to be used in weapons which up until then had relied on natural reservoirs of reactive nitrogen, particularly Peruvian guano, Chilean saltpeter and sal ammoniac extracted from coal. Haber’s discovery fuelled the First World War providing Germany with a home supply of ammonia. This was then oxidized to nitric acid and used to produce ammonium nitrate, nitroglycerine, TNT (trinitrotoluene) and other nitrogen-containing explosives. Since then, reactive nitrogen produced by the Haber–Bosch process has become the central foundation of the world’s ammunition supplies. At the same time, the Haber–Bosch process has facilitated the production of agricultural fertilizers on an industrial scale, dramatically increasing global agricultural productivity in most regions of the world. It is estimated that today the lives of around half of humanity are made possible by nitrogen fertilizers produced via Haber–Bosch process.

2. A World Made of Plastic: The Environmental Problem. Over the last century and a half, chemists have learned how to make synthetic polymers using mainly petroleum and other fossil fuels. Polymers are essentially long chains of atoms, arranged in repeating units. The length and the nature of such repeating units impart to the synthetic polymers unique characteristics in terms of strength, flexibility and weight that make them incredibility useful. During the last 50 years, plastics have become ubiquitous and an essential part of our lives. The first fully synthetic plastic, Bakelite, was invented in 1907 providing a material which was at the same time and electrical insulator, durable and heat resistant. In 1935 Nylon was invented as a synthetic silk to be used during the war for parachutes, ropes and more uses, while Plexiglas became an alternative to glass. The production of plastic boomed in the United States during the Word War II and continued after the war ended opening a new era in which plastics seem to offer a future with abundant material wealth thanks to an inexpensive, safe, sanitary substance that could be shaped by humans to their very whim. However, already in the postwar years, there started to be a shift in the social perception and plastics were no longer seen as unambiguously positive. Plastic debris was first observed in the oceans in the 1960s, some major oil spills and in the same years, and the 1962 Rachel Carson’s book, Silent Spring exposed the dangers of chemical pesticides. As awareness about environmental issues spread, the persistence of plastic waste began to trouble observers. In 1970s and 1980s the social anxiety about waste increased with so many disposable plastic products lasting forever in the environment. Despite the introduction of recycling as a waste-management system most plastics still end up in landfills or in the environment. The ultimate symbol of the problem of plastic waste is the Great Pacific Garbage Patch, which has been described as a swirl of plastic garbage the size of Texas floating in the Pacific Ocean. The reputation of plastics has suffered further thanks to a growing concern about the potential threat they pose to human health. These concerns focus on the additives, such as the much-discussed bisphenol A (BPA) and a class of chemicals called phthalates, that go into plastics during the manufacturing process, making them more flexible, durable, and transparent. Some scientists and members of the public are concerned about evidence that these chemicals leach out of plastics into our food, water, and bodies. In very high doses these chemicals can disrupt the endocrine (or hormonal) system. Researchers worry particularly about the effects of these chemicals on children and what continued accumulation means for future generations. Despite growing mistrust, plastics are critical to modern life as they made possible the development of computers, cell phones, and most of the lifesaving advances of modern medicine. Today scientists are continually developing safer and more sustainable plastics such as bioplastics, made from plant crops instead of fossil fuels, to create substances that are more environmentally friendly than conventional plastics.

The magisterium of Pope Francis has taken a clear position towards the protection of the environment with the Encyclical Letter Laudato Si. In the document the Pope acknowledges the enormous benefits that the sciences have brought about in society, rejoicing in the advancements of technology (Laudato Si, 102). At the same time though he urgently appeals for a ʺnew dialogue about how we are shaping the future of our planetʺ, (…) and calls for ʺa conversation which includes everyone, since the environmental challenge we are undergoing, and its human roots, concern and affect us allʺ (Laudato Si, 14).

3. Towards a Green Chemistry. Chemistry has long been perceived as a dangerous science and often the public associates the word ʺchemicalʺ with ʺtoxicʺ. Over the past three decades, a new awareness on man’s ability to harness chemical innovation while meeting urgent environmental and sustainable economic goals has emerged giving rise to Green Chemistry. Green Chemistry can be defined as the ʺdesign of chemical products and processes to reduce or eliminate the use and generation of hazardous substances.ʺ The central idea of Green Chemistry is that of ʺdesign,ʺ intended as a statement of human intention to achieve sustainability, starting from the molecular level up until the industry sectors. From aerospace, automobile, cosmetic, electronics, energy, household products, pharmaceutical, to agriculture, today there are hundreds of examples of successful applications of economically competitive technologies. The concept of Green Chemistry has gone beyond the research laboratories making an impact in industry, education, environment, and the general public. Chemists have been able more and more to design next generation products and processes so that they are profitable while being good for human health and the environment. A list of Twelve Principles of Green Chemistry has been suggested as a cohesive system to reduce or eliminate intrinsic hazards associated to chemicals and processes. Although a great deal of work has been done to advance Green Chemistry around the world, this still remains an area of great potential in the face of the ecological crisis humanity is facing.

4. Women in Chemistry. Women have contributed to the chemical sciences since the age of alchemy, but for centuries they did so largely unseen and unheard. In the 19^th and much of the 20^th century, women who pursued careers in chemistry often faced intense discrimination and were allowed only ancillary roles in the laboratory. Nowadays women start gaining more prominence in chemical fields. So far five women chemists have received the Nobel Prize for Chemistry. The French-Polish Marie Sklodowska Curie (1867-1934) was the first female Nobel Prize winner and also the first person in history to receive the prestigious award twice: in 1903 in physics for her work on radioactivity together with Henri Becquerel, and in 1911 in chemistry for the discovery of the elements radium and polonium. Marie Sklodowska Curie was an extraordinary woman of acute intellect as well as of strong social and political engagement. Her figure has inspired generations of scientists and today is remembered in the name of universities, institutes of research and charities all over the world. In 1935 Irène Joliot-Curie (1897-1956), Marie Curies’s daughter, also received the Nobel Prize in recognition of her work on the synthesis of new radioactive elements. Dorothy Crowfoot Hodgkin (1910-1994) is awarded the prestigious prize in 1964 for the determination of the structure of penicillin and that of vitamin B12. In the last years other female Nobel laureates in chemistry are Ada Yonath (1939- ) for the successful mapping of the structure of ribosomes (2009) and Frances H. Arnold (1956- ) for the directed evolution of enzymes (2018). Recently the Bank of England opened nominations for the face to adorn the new £50 note for people who have contributed to science. DNA crystallographer Rosalind Franklin (1920-1958), and protein pioneer and Nobel laureate Dorothy Hodgkin (1910-1994) are, among the 200 women, the chemists nominated.

IV. Philosophical questions emerging from the chemical sciences

1. Chemistry and the Origin of Life. The origin of life on our planet is a deeply fascinating one for chemistry. How did complex systems of chemical reactions on the prebiotic Earth lead to living organisms? The issue poses a complex philosophical set of questions, among which, above all, the one about the functions an organism needs to be called ʺliving.ʺ At least three key features are considered essential for this: i) ʺcompartmentalisation,ʺ to maintain its internal environment (presence of cell wall), ii) ʺmetabolism,ʺ to turn external resources (food) into energy (catabolism) and new components of the organism (anabolism) and iii) ʺself-replication,ʺ to reproduce the living organism both in terms of means and information needed for this purpose (proteins and DNA). In 1952 the American chemists Stanley Miller (1930-2007) and Harold Urey (1893-1981) performed a landmark experiment simulating the atmosphere of the early earth with a mixture of water, methane, ammonia and hydrogen. Then through a spark in the gaseous mixture a host of organic and inorganic molecules was produced, including most of the amino acids we see in biological proteins. At the time, proteins were viewed as the main component of cellular systems. This simple experiment showed for the first time that a ʺprimordial soupʺ model for life’s origins, where complex systems of reactions could lead to the synthesis of ever more complex molecules, might be more than a speculation. Only a year after Miller and Urey’s experiment, Francis Crick (1916-2004) and James Watson (1928- ) identify the molecular structure of the DNA. This paved the way to the unveiling of life’s genetic code, which was now seen tied up with nucleic acids, polymers of nucleotide units. Perhaps life could have begun with DNA’s precursor, RNA? RNA could have provided with the information storage needed to get the first living organism started. However, this created a philosophical paradox. The synthesis and replication of RNA itself in fact is carried out by proteins, but the structure of the proteins is encoded by RNA. Leslie Orgel (1927-2007) first proposed that RNA could not only store information but also catalyze the chemical reactions needed to make itself (RNA world hypotheses). Perhaps short sequences of RNA in the primordial soup could have catalyzed the synthesis of identical sequences – they could self-replicate. In time, through slow evolution and building up of new functions, the information-carrying role of RNA would be taken over by the more stable DNA, and the duty of replication taken over by more catalytically versatile proteins. However, ever since the early days of the RNA world hypothesis, the synthesis of RNA from simple building blocks has proved to be extremely challenging to chemists. Even more challenging is to prove the emergence of the genetic code and of life itself just as the outcome of a sophisticate interaction of millions of molecules (enzymes, nucleic acids, metabolites etc.) within the components of a cell. Michael Polanyi (1891-1976) in his excellent and timeless article in Science in 1968, Life’s irreducible structure, looks at the implications of the genetic code and its physical indeterminacy pointing out how life transcends physics and chemistry.

2. A Philosophy of Chemistry. Chemistry has justly been called the central science. Given the unique place that chemistry occupies between physics and biology in the traditional hierarchy of the natural sciences, the discipline has attracted in time increased philosophical attention. Chemistry has traditionally been, and continues to be, the science concerned with the nature of the elements, of substance and indeed of the nature of matter, all traditional philosophical questions. The philosophy of chemistry has gradually emerged as an important area of study within the philosophy of science in its own right. Chemistry poses some very specific chemical issues that have been argued to be worth of specific philosophical attention. One of the most compelling being the very issue of the reduction of chemistry itself to physics. A ʺquantitative reductionʺ through quantum theory and ab initio calculations is often followed to predict quantitative properties such as energies of molecules or bond angles. However, the Schrödinger equation upon which such calculations are based only possesses an exact solution in the case of the hydrogen atom showing that full reduction would never be attainable for even a small molecule. ʺConceptual reductionʺ instead attempts to reduce chemical concepts such as composition, bonding, and molecular structure. According to some philosophers of science, such position is not possible in principle due to the very nature of the concepts themselves and therefore concepts such as composition, bonding, and molecular structure cannot be expressed except than at the chemical level.

3. The Chemical Structure as an Irreducible Structure. Chemistry occupies a central position in epistemology. The chemical level is the first in science where new aspects of the real emerge out of complexity: the molecules. Molecules represent the simplest persistent entity whose extraordinary richness and diversity requires a specific science. In other words, when chemical elements react together to form a new entity, the compound, new properties emerge that are not in a direct and simple relation to those of their own components. In fact, the knowledge of the molecular formula indicating the simple numbers of each type of atom in a molecule very rarely can give us any reasonable idea about the chemical reactivity of the compound. The molecular structure instead – the way the atoms are connected to one another through chemical bonds in the space, determines the properties of the compound and its reactivity. The molecular structure represents therefore the emergent property of the molecule as a complex system. The fact that a molecule is made up of atoms is not denied but in the idea that the molecule will be just-a-bunch-of-atoms cannot be accepted without doubts. The emergence of new properties is manifested also in the interaction of more molecules, as it is evident in supramolecular chemistry.

4. The Periodic Table and the Intelligibility of Nature. The United Nations has proclaimed 2019 as the International Year of the Periodic Table of Chemical Elements (IYPT 2019) to mark the 150 years since its development by Dmitrij Mendeleev. The Periodic Table of the Elements represents one of the most significant achievements in science as a uniting scientific concept. A symbolic representation and an accurate map of our knowledge of the universe. It reveals two very important characteristics of Nature: its intelligibility and relatedness. The possibility for human beings to identify the fundamental chemical elements and cast them in a systematic way into a Table organized in rows and columns according to their atomic number and their electrons reveals the intelligible character of nature. At the same time, it displays the relational aspect of nature not only because the elements are made up of common constituents (protons, electrons and neutrons) but also because the elements are organized in patterns, in a periodic fashion (horizontally) by atomic number (that is the number of protons in each nucleus) and vertically in groups according to the number of electrons on their external orbitals (therefore elements with similar reactivity).