History of the molecule

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For other uses, see: nucleosynthesis, chemical evolution, and molecular evolution

In chemistry, the history of the molecule traces the origins of the concept or idea of the existence, in nature, of a bonded structure of two or more atoms, according to which the structures of the universe are built. In a sense, the concept of fundamental objects in unity similar to the modern concept of molecules and atoms originates from the 5th century BC views of the Greek philosopher Leucippus who argued that all the universe is composed of atoms and voids, and was further developed circa 450 BC by the Greek philosopher Empedocles, who postulated the four "roots"; fire, air, water, earth, as well as then-described "forces" of attraction and repulsion that join these roots. It could be argued that from this form of reasoning, that other further scientists have speculated as to how atoms or roots might exist in unity.

Contents 1 Etymology 2 Early views 3 Middle Ages 4 17th century 5 18th century 6 19th century 7 20th century 8 21st century 9 See also 10 References 11 Further reading 12 External links 12.1 Types 12.2 Definitions 12.3 Articles

[edit] Etymology

According to Merriam-Webster and the Online Etymology Dictionary, the word "molecule" derives from the Latin "moles" or small unit of mass, which is akin to the Greek molos, meaning exertion (c.1548) possibly referring to fact that it takes a certain amount of exertion effort to lift a small mass; or specifically:

Molecule (1794) - "extremely minute particle," from Fr. molécule (1678), from Mod.L. molecula, dim. of L. moles "mass, barrier". A vague meaning at first; the vogue for the word (used until late 18th century only in Latin form) can be traced to the philosophy of Descartes.

[edit] Early views

In about 485 BC, the Greek philosopher Parmenides stated the ontological argument against nothingness, essentially denying the possible existence of a void. In c.460 BC, Greek philosopher Leucippus, in opposition to Parmenides' denial of the void, proposed the atomic theory, which reasoned that everything in the universe is either atoms or voids; a theory which, according to Aristotle, was stimulated into conception so to purposely contradict Parmenides' argument. In the years to follow, specifically in about 450 BC, Leucippus’ pupil Democritus went on to further develop the atomic hypothesis using the term atomos, which means "uncuttable".

In addition to atomic theories and prior to the development of the concept of the "molecule" were the various essential element theories. In the early 6th century BC, the Greek scientist Thales of Miletus reasoned that essential element was water and that all things derived from this element. According to legend, Thales was walking along a hillside path on the shore of Ionia, in what is now called south-western Turkey, and he noticed some rocks which contained fossils of what were unmistakably seashells. This led Thales to believe that the hills must have once been part of the sea. On this logic, Thales reasoned that the original world must have been entirely water, and that this was the essential element.

In the 5th century BC, the Greek Empedocles, being influenced by Pythagoras, claimed that all things consisted of differing combinations of four elements:

The term ‘elements’ (stoicheia) was first used by the Greek philosopher Plato in about 360 BC, in his dialogue Timaeus, which includes a discussion of the composition of inorganic and organic bodies and is a rudimentary treatise on chemistry. Plato assumed that the minute particle of each element had a special geometric shape: tetrahedron (fire), octahedron (air), icosahedron (water), and cube (earth).

Tetrahedron (fire)	Octahedron (air)	Icosahedron (water)	Cube (earth)

Adding to the four elements of the Greeks, in about 350 BC, Aristotle also used the term “element” and conceived of a fifth element called "quintessence", which formed the heavens. Building on this logic, various writers over the years have speculated on possible geometric shapes, such as circles, squares, and polygons, etc., of elements and how these shapes might combine, separate, or possibly rub against each other to create new elements over evolutionary periods.

[edit] Middle Ages

In the Early Middle Ages and into the Middle Ages, from about A.D. 500 to about 1500, there was a general decline or a pause in the development of scientific thought; a direct result of certain fundamental objections of the Christian church and an overall decline in civilization as a whole.^[1] The tenth to the twelfth centuries, however, saw a period of activity, such as is found in the writings of Moses Maimonides, Thierry of Chartres, and William of Conches. These philosophers, while accepting the basic teachings of the theological scriptures, revived the ancient atomic theories to give a scientific interpretation of creation and of the structure of the world.^[1]

Maimonides, for example, primarily relied upon the science of Aristotle and attempted to reconcile the philosophies of the Talmud with alchemy. Thierry of Chartres, following the logic of the four element theories, reasoned that earth and water, being heavier, took a center position in structures, whereas air and fire, being lighter, took an external position. Likewise, William of Conches, being a proponent of the four element theories, reasoned that the elements were divinely created, during the genesis of the world, but that they now operated through the laws of nature. He regarded atoms as "simple and extremely small particles" by which, according to their juxtaposition, all things of the physical world were formed and whereby their sensible qualities were produced. After 1450, with Gutenberg's invention of the printing press, scientific thought began to gain momentum.

[edit] 17th century

The earliest views on the shapes and connectivity of atoms was that proposed by Leucippus, Democritus, and Epicurus who reasoned that the solidness of the material corresponded to the shape of the atoms involved. Thus, iron atoms are solid and strong with hooks that lock them into a solid; water atoms are smooth and slippery; salt atoms, because of their taste, are sharp and pointed; and air atoms are light and whirling, pervading all other materials.^[2] It was Democritus that was the main proponent of this view. Using analogies from our sense experiences, he gave a picture or an image of an atom in which atoms were distinguished from each other by their shape, their size, and the arrangement of their parts. Moreover, connections were explained by material links in which single atoms were supplied with attachments: some with hooks and eyes others with balls and sockets.^[3]

The atomic theory, curiously, was abandoned for nearly two millennia in favor of the various four element theories and later alchemical theories. The 17th century, however, saw a resurgence in the atomic theory primarily through the works of Descartes, Gassendi, and Newton. Using earlier Greek atomic theories to explain how the tiniest particles of matter bonded together, Descartes visualized that atoms were held together by microscopic hooks and barbs.^[4] Subsequently, one of the earliest molecular theories was that put forward by the famous French naturalist René Descartes who believed that some atoms were furnished with hook-like projections, and others, with eye-like ones. He held that two atoms combined when the hook of one got caught in the eye of the other, such as shown below:

By the mid 1770s, it was generally viewed that any theory involving particles endowed with physical hooks was considered “Cartesian chemistry”.^[6] Similar to Descartes, Gassendi, who had recently written book on the life of Epicurus, reasoned that to account for the size and shape of atoms moving in a void could account for the properties of matter. Heat was due to small, round atoms; cold, to pyramidal atoms with sharp points, which accounted for the pricking sensation of severe cold; and solids were held together by interlacing hooks. ^[7]

Newton, though he acknowledged the various atom attachment theories in vogue at the time, i.e. “hooked atoms”, “glued atoms” (bodies at rest), and the “stick together by conspiring motions” theory, rather believed, as famously stated in "Query 31" of his 1704 Opticks, that particles attract one another by some force, which “in immediate contact is extremely strong, at small distances performs the chemical operations, and reaches not far from particles with any sensible effect.” ^[8]

In a more concrete manner, however, the concept of aggregates or units of bonded atoms, i.e. "molecules", traces its origins to Robert Boyle's 1661 hypothesis, in his famous treatise The Sceptical Chymist, that matter is composed of clusters of particles and that chemical change results from the rearrangement of the clusters. Boyle argued that matter's basic elements consisted of various sorts and sizes of particles, called "corpuscles", which were capable of arranging themselves into groups.

In 1680, using the corpuscular theory as a basis, French chemist Nicolas Lemery stipulated that the acidity of any substance consisted in its pointed particles, while alkalis were endowed with pores of various sizes.^[9] A molecule, according to this view, consisted of corpuscles united through a geometric locking of points and pores.

[edit] 18th century

An early precursor to the idea of bonded "combinations of atoms", was the theory of "combination via chemical affinity". For example, in 1718, building on Boyle’s conception of combinations of clusters, the French chemist Étienne François Geoffroy developed theories of chemical affinity to explain combinations of particles, reasoning that a certain alchemical “force” draws certain alchemical components together. Geoffroy's name is best known in connection with his tables of "affinities" (tables des rapports), which he presented to the French Academy in 1718 and 1720.

Étienne François Geoffroy’s 1718 Affinity Table: at the head of the column is a substance with which all the substances below can combine.

These were lists, prepared by collating observations on the actions of substances one upon another, showing the varying degrees of affinity exhibited by analogous bodies for different reagents. These tables retained their vogue for the rest of the century, until displaced by the profounder conceptions introduced by CL Berthollet.

In 1738, Swiss physicist and mathematician Daniel Bernoulli published Hydrodynamica, which laid the basis for the kinetic theory of gases. In this work, Bernoulli positioned the argument, still used to this day, that gases consist of great numbers of molecules moving in all directions, that their impact on a surface causes the gas pressure that we feel, and that what we experience as heat is simply the kinetic energy of their motion. The theory was not immediately accepted, in part because conservation of energy had not yet been established, and it was not obvious to physicists how the collisions between molecules could be perfectly elastic.

In 1789, William Higgins published views on what he called combinations of "ultimate" particles, which foreshadowed the concept of valency bonds. If, for example, according to Higgins, the force between the ultimate particle of oxygen and the ultimate particle of nitrogen were 6, then the strength of the force would be divided accordingly, and similarly for the other combinations of ultimate particles:

[edit] 19th century

Similar to these views, in 1803 John Dalton took the atomic weight of hydrogen, the lightest element, as unity, and determined, for example, that the ratio for nitrous anhydride was 2 to 3 which gives the formula N₂O₃. Interestingly, Dalton incorrectly imagined that atoms “hooked” together to form molecules. Later, in 1808, Dalton published his famous diagram of combined "atoms":

In Amedeo Avogadro's famous 1811 paper "Essay on Determining the Relative Masses of the Elementary Molecules of Bodies", he essentially states, i.e. according to Partington's A Short History of Chemistry, that:^[10]

It must be noted here that this quote is a literal translation. Avogadro uses the name "molecule" for both atoms and molecules. Specifically, he uses the name "elementary molecule" when referring to atoms and to complicate the matter also speaks of "compound molecules" and "composite molecules".

During his stay in Vercelli, Avogadro wrote a concise note (memoria) in which he declared the hypothesis of what we now call Avogadro's law: equal volumes of gases, at the same temperature and pressure, contain the same number of molecules. This law implies that the relationship occurring between the weights of same volumes of different gases, at the same temperature and pressure, corresponds to the relationship between respective molecular weights. Hence, relative molecular masses could now be calculated from the masses of gas samples.

Avogadro developed this hypothesis in order to reconcile Joseph Louis Gay-Lussac's 1808 law on volumes and combining gases with Dalton's 1803 atomic theory. The greatest difficulty Avogadro had to resolve was the huge confusion at that time regarding atoms and molecules – one of the most important contributions of Avogadro's work was clearly distinguishing one from the other, admitting that simple particles too could be composed of molecules, and that these are composed of atoms. Dalton, by contrast, did not consider this possibility. Curiously, Avogadro considers only molecules containing even numbers of atoms; he does not say why odd numbers are left out.

In 1826, building on the work of Avogadro, the French chemist Jean-Baptiste Dumas states:

In coordination with these concepts, in 1833 the French chemist Marc-Antoine-Auguste Gaudin presented a clear account of Avogadro's hypothesis, regarding atomic weights, by making use of “volume diagrams”, which clearly show both semi-correct molecular geometries, such as a linear water molecule, and correct molecular formulas, such as H₂O:

In two papers outlining his "theory of atomicity of the elements" (1857-58), Friedrich August Kekulé was the first to offer a theory of how every atom in an organic molecule was bonded to every other atom. He proposed that carbon atoms were tetravalent, and could bond to themselves to form the carbon skeletons of organic molecules.

In 1856, Scottish chemist Archibald Couper began research on the bromination of benzene at the laboratory of Charles Wurtz in Paris.^[11] One month after Kekulé's second paper appeared, Couper's independent and largely identical theory of molecular structure was published. He offered a very concrete idea of molecular structure, proposing that atoms joined to each other like modern-day Tinkertoys in specific three-dimensional structures. Couper was the first to use lines between atoms, in conjunction with the older method of using brackets, to represent bonds, and also postulated straight chains of atoms as the structures of some molecules, ring-shaped molecules of others, such as in tartaric acid and cyanuric acid ^[12] In later publications, Couper’s bonds were represented using straight dotted lines (although it is not known if this is the typesetter’s preference) such as with alcohol and oxalic acid below:

In 1861, an unknown Vienna high-school teacher named Joseph Loschmidt published, at his own expense, a booklet entitled Chemische Studine I, containing pioneering molecular images which showed both "ringed" structures as well as double-bonded structures, such as:^[13]

Loschmidt also suggested a possible formula for benzene, but left the issue open. The first proposal of the modern structure for benzene was due to Kekulé, in 1865. The cyclic nature of benzene was finally confirmed by the eminent crystallographer Kathleen Lonsdale. Benzene presents a special problem in that, to account for all the bonds, there must be alternating double carbon bonds:

In 1865, German chemist August Wilhelm von Hofmann was the first to make stick-and-ball molecular models, which he used in lecture at the Royal Institution of Great Britain, such as methane shown below:

The basis of this model followed the earlier 1855 suggestion by his colleague William Odling that carbon is tetravalent. Hofmann's color scheme, to note, is still used to this day: nitrogen = blue, oxygen = red, chlorine = green, sulfur = yellow, hydrogen = white.^[14] The deficiencies in Hofmann's model were essentially geometric: carbon was planar, rather than tetravalent, and the atoms were out of proportion, e.g. carbon was smaller in size than the hydrogen.

In 1864, Scottish organic chemist Alexander Crum Brown began to draw pictures of molecules, in which he enclosed the symbols for atoms in circles, and used broken lines to connect the atoms together in a way that satisfied each atom's valence.

The year 1873, by many accounts, was a seminal point in the history of the development of the concept of the "molecule". In this year, the renowned Scottish physicist James Clerk Maxwell published his famous thirteen page article 'Molecules' in the September issue of Nature.^[15] In the opening section to this article, Maxwell clearly states:

After speaking about the atomic theory of Democritus, Maxwell goes on to tell us that the word 'molecule' is a modern word. He states, "it does not occur in Johnson's Dictionary. The ideas it embodies are those belonging to modern chemistry." We are told that an 'atom' is a material point, invested and surrounded by 'potential forces' and that when 'flying molecules' strike against a solid body in constant succession it causes what is called pressure of air and other gases. At this point, however, Maxwell notes that no one has ever seen or handled a molecule.

In 1894, Emil Fischer postulated the famous "Lock and Key" molecule bonding theory. According to this theory, molecules fit together according to complementary geometric shape. Enzymes, for example, are very specific, and Fischer suggested that this was because both the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another.^[16] This is often referred to as "the lock and key" model. An enzyme combines with its substrate(s) to form a short-lived enzyme-substrate complex. However, while this model explains enzyme specificity, it fails to explain the stabilization of the transition state that occurs.

Later, Fisher developed the Fisher projection technique for viewing 3-D molecules on a 2-D sheet of paper:

,

In 1898, Ludwig Boltzmann, in his Lectures on Gas Theory, used the theory of valence to explain the phenomenon of gas phase molecular dissociation, and in doing so drew one of the first rudimentary yet detailed atomic orbital overlap drawings. Noting first the known fact that molecular iodine vapor dissociates into atoms at higher temperatures, Boltzmann states that we must explain the existence of molecules composed of two atoms, the “double atom” as Boltzmann calls it, by an attractive force acting between the two atoms. Boltzmann states that this chemical attraction, owing to certain facts of chemical valence, must be associated with a relatively small region on the surface of the atom called the sensitive region.

Boltzmann states that this "sensitive region" will lie on the surface of the atom, or may partially lie inside the atom, and will firmly be connected to it. Specifically, he states “only when two atoms are situated so that their sensitive regions are in contact, or partly overlap, will there be a chemical attraction between them. We then say that they are chemically bound to each other.” This picture is detailed below, showing the α-sensitive region of atom-A overlapping with the β-sensitive region of atom-B: ^[17]

[edit] 20th century

In the early 1900s, the American chemist Gilbert Lewis began to use dots in lecture, while teaching undergraduates at Harvard, to represent the electrons around atoms. His students favored these drawings, which stimulated him in this direction. From these lectures, Lewis noted that elements with a certain number of electrons seemed to have a special stability. This phenomenon was pointed out by the German chemist Richard Abegg in 1904, to which Lewis referred to as "Abegg's law of valence" (now generally known as Abegg's rule). To Lewis it appeared that once a core of eight electrons has formed around a nucleus, the layer is filled, and a new layer is started. Lewis also noted that various ions with eight electrons also seemed to have a special stability. On these views, he proposed the rule of eight or octet rule: Ions or atoms with a filled layer of eight electrons have a special stability.^[18]

Moreover, noting that a cube has eight corners Lewis envisioned an atom as having eight sides available for electrons, like the corner of a cube. Subsequently, in 1902 he devised a conception in which cubic atoms can bond on their sides to form cubic-structured molecules:

In other words, electron-pair bonds are formed when two atoms share an edge, as in structure C below. This results in the sharing of two electrons. Similarly, charged ionic-bonds are formed by the transfer of an electron from one cube to another, without sharing an edge A. An intermediate state B where only one corner is shared was also postulated by Lewis.

Hence, double bonds are formed by sharing a face between two cubic atoms. This results in the sharing of four electrons:

In 1913, while working as the chair of the department of chemistry at the University of California, Berkeley, Lewis read a preliminary outline of paper by an English graduate student, Alfred Lauck Parson, who was visiting Berkeley for a year. In this paper, Parson suggested that the electron is not merely an electric charge but is also a small magnet (or "magnetron" as he called it) and furthermore that a chemical bond results from two electrons being shared between two atoms.^[19] This, according to Lewis, meant that bonding occurred when two electrons formed a shared edge between two complete cubes.

On these views, in his famous 1916 article The Atom and the Molecule, Lewis introduced the “Lewis structure” to represent atoms and molecules, where dots represent electrons and lines represent covalent bonds. In this article, he developed the concept of the electron-pair bond, in which two atoms may share one to six electrons, thus forming the single electron bond, a single bond, a double bond, or a triple bond:

In Lewis' own words:

Moreover, he proposed that an atom tended to form an ion by gaining or losing the number of electrons needed to complete a cube. Thus, Lewis structures show each atom in the structure of the molecule using its chemical symbol. Lines are drawn between atoms that are bonded to one another; occasionally, pairs of dots are used instead of lines. Excess electrons that form lone pairs are represented as pair of dots, and are placed next to the atoms on which they reside:

To summarize his views on his new bonding model, Lewis states: ^[20]

The following year, in 1917, an unknown American undergraduate chemical engineer named Linus Pauling was learning the Dalton hook-and-eye bonding method at the Oregon Agricultural College, which was the vogue description of bonds between atoms at the time. Each atom had a certain number of hooks that allowed it to attach to other atoms, and a certain number of eyes that allowed other atoms to attach to it. A chemical bond resulted when a hook and eye connected. Pauling, however, wasn't satisfied with this archaic method and looked to the newly-emerging field of quantum physics for a new method.

Subsequently, in 1931, building on theories found in Lewis' famous article, Pauling published his ground-breaking article "The Nature of the Chemical Bond"^[21] (see: manuscript) in which he used quantum mechanics to calculate properties and structures of molecules, such as angles between bonds and rotation about bonds. On these concepts, Lewis developed hybridization theory to account for bonds in molecules such as CH₄, in which four sp³ hybridised orbitals are overlapped by hydrogen's 1s orbital, yielding four sigma (σ) bonds. The four bonds are of the same length and strength, which yields a molecular structure as shown below:

translates into

Owing to these exceptional theories, Pauling won the 1954 Nobel Prize in Chemistry. Notably he has been the only person to ever win two unshared Nobel prizes, winning the Nobel Peace Prize in 1963.

In 1926, French chemist Jean Perrin received the Nobel Prize in physics for proving, conclusively, the existence of molecules. He did this by calculating Avogadro's number using three different methods, all involving liquid phase systems. First, he used a gamboge soap-like emulsion, second by doing experimental work on Brownian motion, and third by confirming Einstein’s theory of particle rotation in the liquid phase.^[22]

In 1937, chemist K.L. Wolf introduced the concept of supermolecules (Übermoleküle) to describe hydrogen bonding in acetic acid dimers. Supermolecules are organized polymolecular systems, held together by non-covalent interactions. Examples of a supermolecules are the Cyclodextrins, which have a cavity in which a guest molecule can fit:

In the mid-twentieth century, neurochemists began to discover molecules that have function in human brain activity. In 1948, for example, Maurice M. Rapport isolated and named the now-famous structure “serotonin”. In the central nervous system, serotonin is believed to play an important role in the regulation of mood, sleep, emesis, sexuality, and appetite. By many accounts, serotonin is considered the “confidence chemical”, in that, for example, cerebral levels of this neurochemical are higher in alpha-males and alpha-females, such as captains, group leaders, and high-ranking chimpanzees in troop hierarchies. Moreover, during the first six months of being in love, paradoxically, serotonin levels in couples drop to 40 percent below those in normal subjects:

Molecular-structure of serotonin (1948)

3D-structure of serotonin C10H12N2O

In 1951, Erwin Müller invents the field ion microscope and is the first to see atoms, e.g. bonded atomic arrangements at the tip of a metal point.

In 1953, American scientists James Watson and Francis Crick determined the molecular structure of DNA or “deoxyribonucleic acid”, which consists of a pair of molecules, organized as strands running start-to-end and joined by hydrogen bonds along their lengths.^[23] Each strand is a chain of chemical "building blocks", called nucleotides, of which there are four types: adenine (abbreviated A), cytosine (C), guanine (G) and thymine (T).^[23] These molcular strands links together in the form a spiral structure, as shown below:

In 1958, the American biochemist George Wald and his co-workers discovered that a photosensitive molecule in the rod cells of the eye, called retinal C₂₀H₂₈O, straightens its configuration in response to light, i.e. photons. This straightened configuration results to trigger a nerve impulse; statistically it takes five photons to trigger such a nerve impulse. This is the core mechanism of the vision process:

For his work, Wald won a share of the 1967 Nobel Prize in Physiology or Medicine with Haldan Keffer Hartline and Ragnar Granit.

During the later half of the twentieth century, computer technologies began to increase; this led to the determination of larger molecular structures such as proteins. In 1958, for example, the structure of the myoglobin molecule was determined using X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew, as shown below, where the colored segments are alpha helices: ^[24]

Perutz and Kendrew received the Nobel Prize in Chemistry for determining the structure of this molecule.

In 1985, Harold Kroto of the University of Sussex, and James Heath, Sean O'Brien, Robert Curl and Richard Smalley, from Rice University, discovered C₆₀ or what is famously known as a "buckyball":

In molecular beam experiments, discrete peaks were observed corresponding to molecules with the exact mass of sixty or seventy or more carbon atoms. Shortly thereafter came the discover the fullerenes. Kroto, Curl, and Smalley were awarded the 1996 Nobel Prize in Chemistry for their roles in the discovery of this class of compounds. C₆₀. Other fullerenes were later noticed occurring outside of a laboratory environment, e.g., such as in normal candle soot.

In 1999, researchers from the University of Vienna demonstrated that the wave-particle duality applied to macro-molecules such as fullerene.^[25]

[edit] 21st century

On the cutting edge is nanotechnology, which is the science and engineering of matter at the atomic scale. In other words, recent areas of interest in the molecular world have been to build functionable molecules atom-by-atom, such as, for example, a molecular gear:

In this direction, for example, in June of 2004 scientists from China's Tsinghua University and Louisiana State University demonstrated the use of nanotubes in incandescent lamps, replacing a tungsten filament in a lightbulb with a carbon nanotube one:

In September of 2005, a research team, led by Ludwig Bartel at the University of California Riverside designed a molecule that walks over a surface like a human, i.e. a walking molecule.^[26] The molecule, 9,10-dithioanthracene or “DTA”, has two linkers that act as feet. With a source of thermal energy, the molecule moves such that only one of the linkers is lifted from the surface while the other stabilizes the molecule and guides its motion. By alternating its two feet, the nano-walker is able to move over atomic surfaces without the assistance of nano-rails or atomic-groves.

Similarly, in October of 2005, researchers at Rice University designed the world's first molecular car.^[27] With a wheelbase of less than 5 nm, the tiny atom-sized car was driven on a gold-plated microscopic highway. The wheels were buckyballs, spheres of pure carbon containing 60 atoms a piece. According to these researchers, this "nanocar" represents the first step towards molecular manufacturing.

The modern theory of molecules makes great use of the many numerical techniques offered by computational chemistry. At the forefront of chemical astronomy, hundreds of molecules have now been identified in interstellar space by microwave spectroscopy.

[edit] See also

• History of chemistry
• History of quantum mechanics
• History of thermodynamics
• History of molecular biology
• Kinetic theory
• Atomic theory

[edit] References

1. ^ ^{a b} Bernard, Pullman; Reisinger, Axel, R. (2001). The Atom in the History of Human Thought. Oxford University Press, 139. ISBN 0195150406. 
2. ^ Pfeffer, Jeremy, I.; Nir, Shlomo (2001). Modern Physics: An Introduction Text. World Scientific Publishing Company, 183. ISBN 1860942504. 
3. ^ See testimonia DK 68 A 80, DK 68 A 37 and DK 68 A 43. See also Cassirer, Ernst (1953). An Essay on Man: an Introduction to the Philosophy of Human Culture. Doubleday & Co., 214. ASIN B0007EK5MM. 
4. ^ Waller, John (2004). Leaps in the Dark: the Making of Scientific Reputations. Oxford University Press, 43. ISBN 0192804847. 
5. ^ Disclaimer: this picture is just for illustration, at the time of Gassendi and Descartes, the composition of water was not known.
6. ^ Comments made by French chemist Guyton de Morveau in about 1772; as found in Kim’s 2003 Affinity That Elusive Dream – A Genealogy of the Chemical Revolution.
7. ^ Leicester, Henry, M. (1956). The Historical Background of Chemistry. John Wiley & Sons, 112. ISBN 0486610535. 
8. ^ (a) Isaac Newton, (1704). Opticks. (pg. 389). New York: Dover.
   (b) Bernard, Pullman; Reisinger, Axel, R. (2001). The Atom in the History of Human Thought. Oxford University Press, 139. ISBN 0195150406. 
9. ^ Lemery, Nicolas. (1680). An Appendix to a Course of Chymistry. London, pgs 14-15.
10. ^ Avogadro, Amedeo (1811). "Masses of the Elementary Molecules of Bodies", Journal de Physique, 73, 58-76
11. ^ Chemical Bonding Concepts – Oklahoma State University
12. ^ Couper’s bond line drawings (1858) – Chemical Achievers
13. ^ Bader, A. & Parker, L. (2001). "Joseph Loschmidt", Physics Today, Mar.
14. ^ W. D. Ollis, "Models and molecules", Proceedings of the Royal Institution of Great Britain, (1972), 45, 1-31).
15. ^ Maxwell, James Clerk, "Molecules". Nature, September, 1873.
16. ^ Fischer E. (1894). "Einfluss der Configuration auf die Wirkung der Enzyme". Ber. Dt. Chem. Ges. 27: 2985-2993. 
17. ^ Boltzmann, Ludwig (1898). Lectures on Gas Theory. Dover (reprint). ISBN 0486684555. 
18. ^ Cobb, Cathy (1995). Creations of Fire - Chemistry's Lively History From Alchemy to the Atomic Age. Perseus Publishing. ISBN 0-7382-0594-X. 
19. ^ Parson, A.L. (1915). "A Magneton Theory of the Structure of the Atom". Smithsonian Publication 2371, Washington.
20. ^ "Valence and The Structure of Atoms and Molecules", G. N. Lewis, American Chemical Society Monograph Series, page 79 and 81.
21. ^ Linus Pauling. The nature of the chemical bond. Application of results obtained from the quantum mechanics and from a theory of paramagnetic susceptibility to the structure of molecules. J. Am. Chem. Soc. 1931, 53 1367-1400.
22. ^ Perrin, Jean, B. (1926). Discontinuous Structure of Matter, Nobel Lecture, December 11.
23. ^ ^{a b} Butler, John M. (2001) Forensic DNA Typing "Elsevier". pp. 14-15. ISBN 0-12-147951-X.
24. ^ Kendrew JC, Bodo G, Dintzis HM, Parrish RG, Wyckoff H, Phillips DC. (1958). A three-dimensional model of the myoglobin molecule obtained by x-ray analysis. Nature 181(4610):662-6.
25. ^ Arndt, M.; O. Nairz, J. Voss-Andreae, C. Keller, G. van der Zouw, A. Zeilinger (14 October 1999). "Wave-particle duality of C60". Nature 401: 680-682. 
26. ^ Pittalwala, M. (2005). "Molecule Walks Like a Human", Sept., Source: UCR Newsroom, Sept. 26
27. ^ Lamba, R. (2005). "Scientist Build World's First Molecular Car", Oct. Source: physOrg.com

[edit] Further reading

• Partington, J.R. (1989). A Short History of Chemistry. Dover Publications, Inc. ISBN 0-486-65977-1. 
• Pert, Candace (1997). Molecules of Emotion. Touchstone Books. ISBN 0-684-84634-9. 
• Atkins, Peter (2003). Atkins' Molecules, 2nd Ed. Cambridge University Press. ISBN 0-521-53536-0. 
• Sargent, Ted (2006). The Dance of Molecules - How Nanotechnology is Changing our Lives. Thunder's Mouth Press. ISBN 1-56025-809-8. 

[edit] External links

• Geometric Structures of Molecules - Middlebury College
• Atoms and Molecules - McMaster University
• Molecular Evolution Table - Institute of Human Thermodynamics
• 3D Molecule Viewer - The Wileys Family
• Molecule of the Month - School of Chemistry, University of Bristol

[edit] Types

• Antibody Molecule - The National Health Museum
• Human Molecule, Earth Molecule, and Sun Molecule - Institute of Human Thermodynamics
• 15 Types of Molecules - IUPAC Definitions

[edit] Definitions

• Molecule Definition - Frostburg State University (Department of Chemistry)
• Definition of Molecule - IUPAC

[edit] Articles

• Molecules Used to Make Nano-sized Containers - TRN Newswire
• Molecular Computer Processors - HP Labs