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Verdigris, a term used to describe the natural green patina that develops on copper and bronze, is often composed of various combinations of copper chlorides, sulphides, sulphates, and carbonates, depending on external factors such sulfur - containing acid rain. The patina is produced in rural areas with pure air by the slow chemical reaction of copper with carbon dioxide and water, which results in a simple copper carbonate.

The final patina is mostly made of sulphide or sulphate compounds in industrial and urban air settings with sulphurous acid rain from coal-fired power plants or industrial activities. Under normal weathering, a patina layer takes many years to develop. A building's patina layers will develop more quickly in damp coastal or marine surroundings than in dry inland ones. When compared to "pure" copper cladding, facade cladding made of copper alloys, such as brass or bronze, will weather differently.

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With copper - alloy cladding, even a permanent gold tint is conceivable, as seen in Colston Hall in Bristol or the Novotel at Paddington Central in London. After the original finish has worn off, steel parts of vintage and well - used weapons frequently develop a film of rust on the action, barrel, or other steel elements. This is what everyone refers to as patina, but gunsmith Mark Novak refers to it as a wonderful thick layer of rust. For a firearm to be preserved and to stop future deterioration, such rust must frequently be removed. 

Chemicals like ammonium sulphide ( blue - black ), liver of sulphur ( brown - black ), cupric nitrate ( blue - green ), and ferric nitrate ( yellow - brown ) are included in the fundamental colour palette for patinas on copper alloys. Patination for artworks is frequently expedited on purpose by heating chemicals. The palette includes deep blues, greens, whites, reds, and a variety of blacks, in addition to matte sandstone yellow. Some patina colours are created by combining pigments applied to chemicals with colours created by the reaction with the metal surface.

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Sometimes waxing, oiling, or applying different kinds of lacquers or clear coatings improves the surface. Simply put, the French sculptor Auguste Rodin used to tell his studio helpers to pee over bronzes that were kept in the garden. Applying vinegar ( acetic acid ) will cause copper to develop a patina. This patina is water - soluble and won't hold up as long on a building's exterior as a "true" patina would. Typically, it serves as a pigment. Slip rings and commutators both have patina.

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Because this kind of patina is created by corrosion, potential airborne contaminants, residue from carbon brush wear, and moisture, it requires particular circumstances in order to function well. Woks and other metal baking ware can also develop patinas. Seasoning is the practise of putting patinas to cookware. A wok's patina is a thick, polymerized layer of oils that have been applied to it to keep food from adhering. A wok's patina may be damaged by scrubbing or soap use, which may also encourage rust. 

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Collectors of knives with carbon steel blades will occasionally apply a patina to the blade to help protect it and give it a more distinctive appearance. You can accomplish this with a variety of chemicals and materials, including mustard, muriatic acid, and apple cider vinegar. Another method is to insert the blade into any acidic fruit or vegetable, such as an orange or an apple. There are different opinions on the worth of patination and its replacement, or repatination, in the case of antiques. 

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A piece's appearance and personality should be preserved because its removal or decrease may significantly lower their worth. Repatination could be advised if the patination has flaked off. Reyne Haines, an appraiser, points out that a metal piece that has been repatinated will be valued less than a piece that still has its original finish, but more than one that has significant patina flaws. 

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Craquelure - Brief Introduction :

A fine pattern of thick cracking that forms on the surface of materials is called a craquelure. It may be brought on by ageing, drying, patterning done on purpose, or a mix of all three. The phrase is most frequently used to describe tempera or oil paintings, though it can also appear in antique ivory sculptures or painted miniatures mounted on ivory. Authenticating artwork has recently been suggested using craquelure analysis. "Crackle" is the term used in ceramics to describe the craquelure that occurs in ceramic glazes, where it is frequently a desirable appearance. 

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It is a specific feature of Chinese Ge pottery. This is typically distinguished from crazing, a glaze firing flaw or an ageing or damage - related phenomenon. The type of drying oil or paint media employed and the presence of paint additives, such as organic solvents, surfactants, and plasticizers, determine the complexity and mechanical properties of painting systems. Understanding the process by which paint craquelures form and the morphology of the ensuing cracks reveals information about the tools and supplies employed by the artists. 

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Identification of the morphology of craquelure can be accomplished. The following list of seven important characteristics is used to characterise the morphology of craquelure. Local and global fracture direction, association with weave or grain direction of support, crack shape, crack spacing, thickness, crack termination, and network organisation are all factors to consider. The identification of "styles" of craquelure, which connect fracture patterns to different historical schools of painting, has been done using these seven criteria.

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This establishes a connection between the fracture patterns and certain places, times, and painting techniques. Italian panel paintings from the 1300s to 1500s: unique secondary networks of thin cracks and perpendicular to wood grain fissures with jagged edges. Flemish paintings on panel ( c. 1400 – 1600 ) : smooth, straight segments of cracks with an orientation parallel to the wood grain, as well as small, square islands, are noticed. Dutch canvas paintings from the 1600s : the principal axis of the picture is cracked perpendicularly, with jagged lines and square joints. 

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The cracks typically follow the weave and weft of the canvas support. French paintings on canvas from the 1700s : random distributions of non-directional cracks with smooth, curving lines. Freshly formed, stiffer sublayers tended to delocalize strain from the support and eliminate the relationship between crack direction and canvas weave. Because of the wood, animal glue, gesso, paint, binder, and other materials employed, paintings do not have flat surfaces; rather, they have an uneven texture.

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Surface textures might differ depending on the place they were generated in much as the components used to make paintings differ by geography. Italian paintings' thin ground surfaces resulted in their paintings' slim, thin cracks, whilst French paintings' much broader ground surfaces resulted in their paintings' extremely swirly cracks. The pictorial layer tends to contract when the volatile solvents evaporate during drying.

Large tensile strains in the top paint layer are induced by non - uniform shrinkage over the painting surface as a result of different paint species' unequal adherence to the sublayer. The amount of adhesion to the sublayer, paint film thickness, composition, and the mechanical characteristics of the sublayer all have a significant role in crack formation during drying. Within days of painting, craquelure, which was created during the drying process, manifests as little cracks that are restricted to the uppermost paint layers.

Capillary forces, which limit drying stresses to the painting's free surface, are the cause of this localisation. Due to the fine dispersion of pigment particles within the evaporating volatile liquids, drying cracks are typically isotropic. An unfavourable rise in surface energy as the fracture lengthens inhibits crack propagation at a critical strain, while an increase in the elastic energy of the material nearby encourages it. Fracture mechanics allows for a precise evaluation of the circumstances surrounding the propagation of a drying crack. 

The degree to which the top paint coat adheres to the sublayer greatly affects the width of the crack. The graphic layer can slip over the sublayer and produce spectacular, wide cracks as a result of uneven tensile strains during solvent evaporation if there is inadequate adhesion between these layers. As a result, the breadth of drying cracks varies greatly in contrast to ageing cracks. If the painter applies too much oil or another fatty component to the sublayer material, poor adherence may result. 

The pictorial layer will not crack if the film thickness is below a certain value. Thin coatings prevent cracks from spreading because the reduction in elastic energy that occurs when a crack lengthens is insufficient to counteract the corresponding rise in surface energy. Networks of cracks can be seen in films that are thicker than this crucial value.

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Thick films exhibit more complete networks because the degree of connectivity between nucleation sites grows with film thickness, whereas thicknesses close to the critical value are characterised by isolated star - shaped fracture junctions. The support, or sublayer,'s degree of stiffness has a significant impact on the crack spacing during drying. The strain in the visual layer is not caused by an infinitely rigid sublayer. During the drying process, changes in the relative humidity have an impact on a painting's support and ground layer, which encourages crack growth.

Paintings made of hygroscopic materials, such as gesso ground layers or wood supports, are particularly sensitive to changes in relative humidity. At relative humidities ( RH ) below 75%, gesso is brittle; as RH rises, gesso loses stiffness and changes to a ductile condition. Variations in RH result in highly uneven tensile strains across the surface of the gesso, which fractures as the material contracts during drying. During the drying process of the gesso, craquelure is quite obvious. 

Similar to this, wood supports react strongly to variations in RH. When exposed to moisture, wood grains frequently expand perpendicular to the grain axis. When a wet ground layer is put to a wood support's surface, the wood in contact with the layer swells while the panel's back stays the same. This may be a factor in cupping, a condition when a panel of wood begins to bow transverse to the grain of the wood. As the ground layer dries, the additional forces on the convex side of the cupped wood panel induce further fracture. 

Aged cracks differ from their drying counterparts in that they are more pronounced, deeper, and form throughout the course of the painting's lifetime. Because it is dependent on the precise environmental changes and chemical ageing processes the paint is subjected to, this sort of craquelure is far more challenging to forecast and model. 

Direct impacts, differences in temperature and relative humidity, support deformation, restoration procedures such as canvas reinforcing and stretching, and oxidation reactions that render the surface chalky or more brittle are important factors that contribute to ageing craquelure. The pictorial layer generally gets brittler with age, making it less able to withstand the forces brought on by the environment. There are many ways to make induced craquelure, and forgers of Old Master paintings, which naturally have some, frequently use it in their works.

Eric Hebborn, an art forger, created a method, and Tony Tetro found a way to use formaldehyde and a unique baking procedure. Although there are several techniques, like baking or completing a painting, through which this is tried, craquelure is virtually impossible to perfectly recreate artificially in a particular pattern. However, although genuine craquelure includes cracks with varied patterns, these techniques typically produce cracks that are homogeneous in appearance. Using zinc white paints as the underlayer in pentimento techniques frequently results in craquelure. 

Because the smaller zinc oxide particles do not attach to the sublayer, they are better at causing craquelure than bigger particles. Additionally, craquelure is more easily produced by zinc white paints employing linoleic acid-based binders than by paints using other binders. Craquelure, which affects the glaze of ceramics, can form over time but can also be intentionally used as a decorative element. This practise has a long history, particularly in Chinese and Korean pottery.

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The term "crackle" typically refers to these intentional glazing characteristics, with names like "crackle glaze" or "crackle porcelain" being used frequently. Although sometimes experts have trouble determining if lesser effects are intended or not, it is commonly distinguished from crazing, which is incidental craquelure coming from a glaze flaw. Some might have only emerged with time. Guan pottery and Ge ware, two prominent Chinese ceramics from the Song and Yuan eras, feature purposeful crackle glazes. 

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In Ru ware, the gentler crackle may be accidental, though the majority of pieces do. "Gold thread and iron wire" double crackle, a form of double crackle found in Ge ware, is characterised by two patterns: one with a coarser network and the other with a wide and big crackle. The appearance of each set of cracks has been enhanced by the application of a tinted stain in a variety of colours. There are several glazing layers, and the broader crackling appears first before the finer one does so inside of those regions.

The quick cooling and possibly low silica content in the glaze are the main causes of the crackling, which may not occur right away after fire. The craquelure technique has been employed by the modern decor industry to produce a variety of items made of materials like glass, ceramics, and iron. The usage of marketing kits that react with the colours found in ornamental acrylic colours allowed for this. The percentage of reagent and period of application both affect how much craquelure is created.

Glitter powder, which is often available in copper, bronze, and gold, is used to draw attention to the fractures. When several brands of pre-made goods are combined to resemble craquelure, the resulting fractures come in a variety of shapes and sizes. Digital photographs can have craquelure by using software programmes. There are techniques for detecting art forgeries that make use of craquelure. Historical craquelure patterns are hard to replicate, making them an effective tool for verifying the authenticity of works of art.

MudCracks - A Review : 

With great accuracy, contemporary detection approaches use feature extraction at fracture junctions and picture matching to determine the authenticity of artwork. Mudcracks are sedimentary structures that develop as muddy material dries and shrinks. They are also known as mud cracks, desiccation cracks, or cracked mud. As a result of a decrease in water content, crack formation also happens in soils that contain clay. Wet, muddy sediment dries up and contracts, which is how naturally occurring mudcracks begin.

The substance below maintains its size as the upper layer shrinks, causing a strain to form. Channel fractures begin to form in the dried-up surface when the tension gets too great, relieving the pressure. Individual fissures grow and link, creating a polygonal, interconnected network of shapes known as "tesselations." The polygon begins to curl upward if the strain is allowed to increase. Geologists can utilise this property to determine a rock's initial orientation. Sediment may later cover cracks, creating casts over the base. 

Instead of being exposed to the air and drying out, syneresis cracks are structurally comparable features that develop from the underwater shrinkage of murky silt brought on by variations in salinity or chemical conditions. Due to their propensity to be discontinuous, sinuous, and trilete or spindle - shaped, syneresis cracks can be distinguished from mudcracks. When viewed from above, mudcracks often have a polygonal shape and a v-shaped cross section. The crack tapers downward and the "v" opens near the top of the bed.

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Mudcracks can be categorised according to their completeness, orientation, shape, and kind of infill, according to Allen's ( 1982 ) proposal. A network of connected tessellating mudcracks is formed. Cracks frequently connect when smaller, discrete cracks come together to form a bigger, continuous crack. Mudcracks that are not complete form in the same region as other cracks while not being related to them. It is possible for orthogonal junctions to be random or to have a preferred orientation.

Oriented orthogonal cracks are typically complete, connect to one another, and form irregular polygonal forms, frequently in rows. Random orthogonal cracks lack connections and general shapes because the cracks are incomplete and unoriented. They are not entirely geometric, while not making general shapes. Mudcracks that are not orthogonal have a geometric pattern. They develop as a single three - pointed star shape made up of three cracks in unfinished non - orthogonal fissures.

Although more than three cracks could also emerge, three are typically regarded as the minimum. They create a very geometric pattern when non-orthogonal cracks are fully developed. Small polygonal shaped tiles in a repeated pattern are what the pattern resembles. During one of the last phases of desiccation, mud curls develop. On the exposed top layer of very lightly bedded mud rocks, mud curls are frequently seen. When mud curls develop, the water present in the sediment starts to evaporate, which separates the layered layers.

The top layer can compress and create curls while desiccation takes place since it is significantly weaker than numerous levels. Mud curls may be maintained as mud - chip rip - up clasts if carried by later currents. Mudcracks develop naturally in silt that has previously been saturated with water. Mudcracks are found in places like dried ponds, floodplain muds, and abandoned river channels. Mudcracks may also indicate a formation environment that was primarily sunny or shaded.

Widely scattered, irregular mudcracks are the result of rapid drying in bright surroundings, but closer-spaced, more regular mudcracks show that they formed in a shady location. Similar characteristics can also be found in igneous dykes and sills, columnar basalt flows, and frozen ground. Ceramic glazes, paint films, and improperly constructed concrete are examples of man - made materials that can develop polygonal crack networks that resemble mudcracks.

Utilising technical thin films created using micro- and nano technologies, mudcrack patterning at finer sizes can also be detected and analysed. Mudcracks can be preserved as castings on the underside of an overlying layer or as v - shaped fissures on the top of a bed of muddy silt. The cracks still have the same appearance as when they were first formed when they are preserved on top of a bed. The fractures are filled in with more recent, atop-lying silt when they are preserved on the base of the bedrock.

The part that sticks out most in most bottom - of - bed instances are the cracks. When newly created, fully dried mudcracks are covered in fresh, wet sediment and buried, bottom - of - bed preservation takes place. The newly moist sediment is further forced into the fissures where it dries and hardens by burial and pressure. Later, erosion exposes the mud - cracked rock.

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In these situations, the older material that fills the openings will degrade more quickly than the initial mud cracks. Geologists utilise this kind of mudcrack to identify the vertical orientation of rock samples that have undergone folding or faulting. 

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Crazing - An Explanation : 

Crazing is a phenomena that causes a network of tiny cracks to appear on a material's surface, such as in a glaze layer. In some thermoplastic glassy materials, crazing frequently occurs before fracture. The plane of the crazing correlates to the direction of tension because it only occurs under tensile stress. Because the crazing region has a different refractive index from the surrounding material, the effect may be easily distinguished from other types of tiny cracking.

Interpenetrating microvoids and tiny fibrils form as a result of crazing, which takes place in areas of high hydrostatic stress or intense localised yielding. The microvoids expand and coalesce as a result of the bridges breaking if a sufficient tensile load is applied; as the microvoids coalesce, cracks start to form. Because the substance is held together by a mixture of stronger covalent connections and weaker Van der Waals forces, crazing happens in polymers. The Van der Waals force is overcome by sufficient local tension, allowing for a small gap.

Covalent bonds that hold the backbone chain together prevent the gap from getting any wider once the slack has been removed. The holes in a frenzy are extremely small. Light reflects off the surfaces of the gaps, making crazes visible. Fine filaments known as fibrils, which are molecules of the stretched backbone chain, fill the gaps. A light microscope cannot see the fibrils since they are only a few nanometers in diameter, but an electron microscope can make them out. 

The profile of a crazing's thickness is similar to that of a sewing needle: the crazing's very tip could be as thin as several atoms. It tends to gradually thicken as you get further away from the tip, with the rate of increase slowing down as you get farther away. As a result, the distance from the tip at which crazing develops is crucial. Between 2° and 10° is the range of the crazing's opening angle. The microstructure of the crazing can be reduced down to 20 or less, making it only visible via electron microscopy.

The boundary between the crazing and surrounding bulk polymer is exceedingly crisp. In contrast to a crack, a craze can continue to support a weight while being imperceptible from the outside. Additionally, the process of craze formation before cracking absorbs fracture energy and significantly raises a polymer's fracture toughness. It has been discovered that the initial energy absorption per square metre in a craze region can be up to several hundred times greater than that of the uncrazed region, but it gradually declines and levels off.

Extremely stressed areas with blemishes, defects, stress concentrations, and molecular inhomogeneities are where crazes develop. Generally, crazes spread perpendicular to the stress being applied. Most amorphous, brittle polymers, including polystyrene ( PS ), acrylic ( PMMA ), and polycarbonate, are susceptible to crazing, which is characterised by a whitening of the affected area. Light dispersion from the crazes is what gives the object its white tone. 

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The process that results in crazing is reversible. As soon as compressive stress or a temperature that is greater than the temperature at which glass transforms is applied, the crazing may vanish and the materials will resume their optically homogenous state. When thermoplastic materials are deformed, shear banding a narrow region with a high level of shearing strain from local strain softening is frequently observed. Crazing and shear banding differ significantly in that shear banding does not occur with an increase in volume but crazing does.

As a result of the volume contracting instead of expanding during compression, many of these brittle, amorphous polymers will shear band rather than craze. Additionally, "necking," or the focus of force on one area of a material, is often not seen when crazing occurs. Instead, uniform crazing will take place all over the material. Thermoplastic polymers are frequently strengthened with rubber particles. Stress concentrators are particles that have higher compliance and are, as a result, softer than the surrounding matrix.

These areas of intense tension start crazes, which spread in the direction opposite to the force being applied. This explains a phenomena known as "multiple crazing" that, in the case of HIPS, provides flexibility to otherwise brittle polymer matrices. After adjustment, there will be a significant improvement in the capacity to absorb energy. Even brittle - ductile transition is possible for some brittle plastic materials. Previously, it was thought that the rubber particles were the main cause of the enhanced energy absorption. 

It was suggested that rubber particles might congregate at crack tips under tension and prevent crack propagation, or that rubber particle contraction caused a decrease in the matrix's glass transition temperature. However, studies revealed that only 10% of the total energy was absorbed by the rubber particles, and that the rubber - caused drop in glass transformation temperature was only about 10 K, which was insufficient for the matrix to yield at room temperature. 

When the stress is less than the fracture strength, Schmitt and Bucknall discovered the existence of stress whitening and shear yielding, which led to the development of the rubber toughening process. They suggested that the rubber particles acted as the point of concentration for stress, which started the matrix material's metamorphosis from brittle to ductile and yielded. To be more specific, yielding manifests as crazing or shear band, which can use up a significant amount of the deformation energy. 

Glassy polymers are susceptible to crazing when exposed to environmental factors. It is problematic since it occurs at considerably lower stress conditions and occasionally after a long delay, making it difficult to identify and prevent. PMMA containers, for instance, are quite resistant to humidity and temperature in everyday usage without any obvious flaws. When they are wet with gin after being machine washed and left in the air for one or two days, they may shudder suddenly. 

Although there is little tension placed on the containers during the procedure, crazing is nevertheless there. There are various theories that have attempted to explain the environmental factors that contribute to the creation of crazing, but surface energy reduction and plasticization are among the most well-established and commonly accepted. Many techniques, including surface coating and stress reduction, are used to prevent environmental crazing and cracking.

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However, because of the complicity of environmental impacts, particularly those in organic environments, it is difficult to come up with a universal fix and entirely eliminate the effect. When proper concrete practises are not followed, crazing can also be noticed on single - ply roofing membranes, joint sealant, and concrete itself. A flaw in glazed pottery's glaze is crazing. It is characterised by cracks that pierce the glaze in the form of a spider web design and is brought on by tensile tensions that are too strong for the glaze to handle.

In ceramics, the distinction between "crackle"—when the same occurrence is intentionally manufactured and frequently dramatically accentuated—and "crazing," which occurs accidentally, is frequently made. The unpredictable effects of crackling were particularly beloved by the Chinese, and whereas in Ru ware it appears to have been a quality that was generally tolerated but not sought after, in Guan china a strong crackle was a desired effect. Odontology also uses the term "crazing" to describe tiny fissures in tooth enamel. 

Crazy's English root meaning, "to shatter, crush, or break," first appeared in the 1300s. Pottery crazing is where the metaphorical senses we use now first arose. Crazy first appeared as "diseased or sickly" around 1570, and "of unsound mind" around 1610. According to the context, the term may or may not include ions that meet this requirement. A molecule is a collection of two or more atoms held together by the attractive forces known as chemical bonds.

Molecules - A Deep Dive : 

When speaking of polyatomic ions, the distinction between them and ions is frequently ignored in the fields of quantum physics, organic chemistry, and biochemistry. A molecule can be heteronuclear, which is a chemical compound made up of more than one element, such as water ( two hydrogen atoms and one oxygen atom; H2O ), or homonuclear, which is a molecule made up of atoms of one chemical element, such as the two atoms in the oxygen molecule ( O2 ).

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The term "molecule" is frequently used to refer to any gaseous particle, regardless of its composition, in the kinetic theory of gases. Since the noble gases are single atoms, the requirement that a molecule comprise two or more atoms is relaxed. Commonly, single molecules do not include atoms and complexes joined by non - covalent interactions like hydrogen bonds or ionic bonds. Although discussions of concepts like molecules date back to antiquity, contemporary research into the nature of molecules and their links only started in the 17th century.

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The study of molecules is now referred to as molecular physics or molecular chemistry. It has been developed over time by scientists including Robert Boyle, Amedeo Avogadro, Jean Perrin, and Linus Pauling. As our understanding of molecular structure has grown, so has the definition of a molecule. Molecules are the smallest particles of pure chemical substances that nevertheless retain their composition and chemical properties, according to earlier definitions that were less accurate.

Many everyday objects, such as rocks, salts, and metals, are built of massive crystalline networks of chemically connected atoms or ions rather than discrete molecules, which causes this definition to frequently fail. The prescientific ancient Greek philosophers Leucippus and Democritus, who maintained that the cosmos is made up entirely of atoms and voids, are the originators of the current notion of molecules. Approximately 450 BC, Empedocles proposed the existence of four basic elements, viz., fire, earth, air, and water.

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As well as, "forces" of attraction and repulsion that allowed the elements to coexist. It was believed that the incorruptible quintessence aether, a fifth element, was the essential component of the heavenly bodies. Aristotle adopted the philosophy of Leucippus and Empedocles, along with the aether, and transmitted it to Europe during the Middle Ages and the Renaissance. 

However, in a more concrete sense, Robert Boyle's 1661 hypothesis that matter is made up of clusters of particles and that chemical change results from the rearrangement of the clusters, which was published in his renowned work The Sceptical Chymist, is where the idea of aggregates or units of bonded atoms, i.e. "molecules," originates. Boyle asserted that "corpuscles," which come in a variety of shapes and sizes and are capable of forming groups, are the building blocks of matter.

William Higgins' thoughts on what he referred to as combinations of "ultimate" particles, which prefigured the idea of valency bonds, were published in 1789. According to Higgins, the force would be distributed appropriately if, for instance, the force between the ultimate particles of oxygen and nitrogen was 6, and similarly for the other combinations of ultimate particles. The phrase "molecule" was coined by Amedeo Avogadro.

According to Partington's A Short History of Chemistry, the smallest particles of gases are not always simple atoms; rather, they are composed of a certain number of these atoms bound together by attraction to form a single molecule. This is what he basically states in his 1811 paper "Essay on Determining the Relative Masses of the Elementary Molecules of Bodies". In accordance with these ideas, Marc Antoine Auguste Gaudin, a French chemist, in 1833 presented a clear explanation of Avogadro's hypothesis.

It was regarding atomic weights, by using "volume diagrams," which clearly show both correct and semi-correct molecular formulas, such as H2O, and semi - correct molecular geometries, such as a linear water molecule. Linus Pauling, an unidentified American undergraduate chemical engineer, was studying the Dalton hook - and - eye bonding method in 1917, which at the time was the standard way to describe bonds between atoms. Pauling, however, wasn't happy with this approach and searched for an alternative in the recently developed science of quantum physics.

The existence of molecules was definitively shown by French physicist Jean Perrin, who won the Nobel Prize in physics in 1926 for his work. He achieved this by employing three separate techniques to calculate the Avogadro constant, all of which used liquid phase systems. He began by creating an emulsion that resembled gamboge soap, followed by experiments on Brownian motion, and finally, he verified Einstein's theory of particle rotation in the liquid phase. 

The exchange forces, saturable, nondynamic forces of attraction and repulsion, of the hydrogen molecule were addressed in 1927 by the physicists Fritz London and Walter Heitler. Their joint paper's handling of the valence bond in this topic was significant since it subsumed chemistry under quantum mechanics. Pauling, who had recently gotten his PhD and had travelled to Heitler and London on a Guggenheim Fellowship while based in Zürich, was influenced by their work. 

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Pauling published his groundbreaking article "The Nature of the Chemical Bond" in 1931, building on the theories found in Lewis' well-known article and the work of Heitler and London. In this article, Pauling utilised quantum mechanics to calculate properties and structures of molecules, such as angles between bonds and rotation about bonds. Pauling built his hybridization theory on these ideas to explain bonds in compounds like CH4, which has four sp3 hybridised orbitals that overlap with hydrogen's 1s orbital to form four sigma bonds.

A molecular structure results from the identical length and strength of the four bonds. Depending on whether chemistry or physics are the main topics, the study of molecules is referred to as molecular chemistry or molecular physics. While molecular physics is concerned with the principles guiding the structure and functions of molecules, molecular chemistry deals with the laws governing the interactions between molecules that cause chemical bonds to form and break. However, in actuality, this distinction is ambiguous.

A molecule is a stable system ( bound state ) made up of two or more atoms in the field of molecular sciences. Sometimes it helps to think of polyatomic ions as electrically charged molecules. The phrase "unstable molecule" refers to highly reactive species, which include fleeting collections ( resonances ) of electrons and nuclei like radicals, molecular ions, Rydberg molecules, transition states, van der Waals complexes, or groups of colliding atoms like Bose-Einstein condensate. 

There are lots of molecules in matter. Most of the oceans and atmosphere are also made up of them. The majority of organic compounds are molecules. Molecules such as proteins, the amino acids that make them up, nucleic acids ( DNA and RNA ), sugars, carbohydrates, lipids, and vitamins are examples of the constituents of life. The nutrition minerals, such as iron sulphate, are often ionic compounds rather than molecules. On Earth, however, the vast majority of known solids are composed entirely or mostly of molecules - free crystals or ionic compounds.

All the minerals that make up the Earth's composition, as well as sand, clay, pebbles, rocks, boulders, bedrock, the molten interior, and the Earth's core, are among them. All of these are composed of several chemical linkages but lack recognisable molecules. Although salts and covalent crystals are frequently made of repeating unit cells that stretch either in a plane, as in graphene, or three dimensions, as in diamond, quartz, and sodium chloride, neither of them can be described as conventional molecules.

The majority of metals, which are in condensed phases with metallic bonding, follow the same pattern of repetitive unit-cellular structure. As a result, molecules do not make up solid metals. Glasses are solids that have vitreous disorganised atoms holding them together with chemical bonds rather than any discernible molecules or the regular unit - cellular structure that distinguishes salts, covalent crystals, and metals. Covalent bonding typically holds molecules together.

Numerous non - metallic elements do not exist in the environment as free atoms, but rather as molecules, either as homonuclear molecules or in compounds. Take hydrogen, for instance. Some claim that a metallic crystal can be thought of as a single massive molecule held together by metallic bonds, but others point out that metals behave very differently from molecules. A chemical bond known as a covalent bond entails the exchange of electron pairs between atoms.

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When atoms share electrons, the permanent equilibrium of attractive and repulsive forces between them is referred to as covalent bonding. These electron pairs are known as shared pairs or bonding pairs. The main interaction in ionic compounds is ionic bonding, a form of chemical bond involving the electrostatic attraction between ions with opposing charges. Atoms that have gained or lost one or more electrons are referred to as anions while atoms that have gained or lost one or more electrons are referred to as cations.

In contrast to covalence, this transfer of electrons is referred to as electrovalence. The cation and anion are nonmetal atoms in the most basic scenario, however these ions can also be more complex, such as molecular ions like NH4+ or SO42. Ionic bonding typically results in solids (or occasionally liquids) without distinct molecules at normal temperatures and pressures, but vaporisation or sublimation of such materials does result in distinct molecules where electrons are still transferred fully enough for the bonds to be considered ionic rather than covalent. 

The majority of molecules are much too small to be seen with the human eye, although certain polymer molecules, particularly biopolymers like DNA, can grow to macroscopic quantities. A few angstroms to several dozen angstroms, or around one billionth of a metre, is the size range of molecules that are frequently utilised as the building blocks for organic synthesis. As mentioned above, single molecules cannot typically be seen with the naked eye, although small molecules and even the silhouettes of individual atoms can occasionally be traced using an atomic force microscope. 

Supermolecules or macromolecules are some of the biggest molecules. The diatomic hydrogen molecule ( H2 ), with a bond length of 0.74, is the smallest known molecule. The size a molecule appears to be in solution is called the effective molecular radius. Examples can be found in the table of perm selectivity for various compounds. A molecule's chemical formula consists of one line of chemical element symbols, numbers, and occasionally additional symbols like brackets, dashes, brackets, plus (+) and minus (-) signs.

These are restricted to a single typographic line of symbols, which may also contain superscripts and subscripts. An extremely basic kind of chemical formula is the empirical formula for a substance. It is made up of the simplest integer ratio of the constituent chemical elements. For instance, ethanol ( ethyl alcohol ) is always composed of carbon, hydrogen, and oxygen in a 2 : 6 : 1 ratio, while water is always formed of atoms of hydrogen and oxygen in a 2:1 ratio. However, this does not specifically identify the type of molecule; for instance, ethanol and dimethyl ether have the same ratios.

Isomers are molecules with the same atoms arranged in several ways. The empirical formula for carbohydrates, for instance, is the same ( carbon : hydrogen : oxygen = 1 : 2 : 1 ) but the overall number of atoms in the molecule varies. The molecular formula identifies various molecules by revealing the precise amount of atoms that make up each one. Although they are separate molecules, different isomers can share the same atomic structure. The empirical formula and the molecular formula are frequently identical, but not always.

Acetylene, for instance, has the chemical formula C2H2, yet CH is the simplest integer ratio of the elements. The chemical formula can be used to compute the molecular mass, which is expressed in traditional atomic mass units as 1 / 12 of the mass of a neutral carbon - 12 ( 12C isotope ) atom. The phrase "formula unit" is used in stoichiometric calculations for network solids.

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A straightforward molecular formula or even a semi - structural chemical formula might not be sufficient to accurately describe a molecule with a complex three - dimensional structure, particularly one with atoms bound to four separate substituents. In this situation, a structural formula, a graphical sort of formula, might be required. A one - dimensional chemical name can be used to describe structural formulations, however this involves many phrases and terms that are not included in chemical formulas. 

Molecules continuously oscillate through vibrational and rotational motions about set equilibrium geometries, or bond lengths and angles. The molecules that make up a pure substance all have the same typical geometrical structure. A molecule's qualities, especially its reactivity, are largely determined by its chemical formula and structural makeup. Although they have the same chemical formula, isomers typically have vastly distinct properties due to their unique structures.

One sort of isomer, called a stereoisomer, can have highly identical physical and chemical characteristics and yet differing biological actions. The subject of molecular spectroscopy is the response ( spectrum ) of molecules to known - energy ( or known - frequency, according to the Planck relation ) probing signals. By monitoring the molecule's energy exchange through absorbance or emission, one can determine the quantized energy levels of a given molecule.

Generally speaking, diffraction investigations involving high energy X - rays, neutrons, or electrons interacting with a regular arrangement of molecules ( such as in a crystal ) are not considered to be part of the scope of spectroscopy. In order to detect molecules in space, microwave spectroscopy can be used to observe changes in the rotation of molecules. The vibration of molecules, including their stretching, bending, and twisting motions, is measured using infrared spectroscopy.

It's frequently used to describe the many types of bonds or functional groups that make up molecules. Colour is produced by variations in electron configurations, which give rise to absorption or emission lines in ultraviolet, visible, or near - infrared light. Nuclear resonance spectroscopy can be used to characterise the numbers of atoms in various places in a molecule by measuring the surroundings of certain nuclei in the molecule. 

The knowledge of the chemical bond depends on the study of molecules by molecular physics and theoretical chemistry, which is largely based on quantum mechanics. The hydrogen molecule - ion, H2+, is the simplest type of molecule, and the one - electron link is the most basic type of chemical connection. Two positively charged protons and one negatively charged electron make up H2+, which makes it easier to solve the Schrödinger equation for the system because there is no electron - electron attraction.

One of the key components of computational chemistry is the ability to estimate solutions for more complex compounds thanks to the development of fast digital computers. According to IUPAC, a molecule "must correspond to a depression on the potential energy surface that is deep enough to confine at least one vibrational state" in order to be deemed to be an arrangement of atoms that is sufficiently stable to be referred to as a molecule. Only the intensity of the interaction matters for this definition, not the type of interaction between the atoms.

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In fact, it includes weakly bound species that aren't typically thought of as molecules, like the helium dimer He2, which has just one vibrationally bonded state and is so loosely bound that it is most likely to be found at very low temperatures. An operational definition of a molecule is whether or not a configuration of atoms is sufficiently stable to be referred to be one. Therefore, from a philosophical perspective, a molecule is not a fundamental thing, in contrast to, say, an elementary particle. 

Rather, the idea of a molecule is the chemist's way of expressing relevant information about the potencies of atomic - scale interactions in the physical world that we experience. 

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Atoms - A Broad Discussion : 

A particle called an atom has a nucleus made up of protons and neutrons that is encircled by an electron cloud. The fundamental unit of the chemical elements is the atom, and the protons in an atom serve as a means of differentiating one chemical element from another. Any atom with 11 protons, for instance, is sodium, while any atom with 29 protons is copper. The element's isotope is determined by the number of neutrons in it. Atoms are incredibly tiny, measuring typically 100 picometers across. About a million carbon atoms make up an average human hair.

Since this is smaller than the visible light spectrum's smallest wavelength, people cannot view atoms using standard microscopes. Because of quantum phenomena, atoms are so tiny that it is impossible to predict their behaviour with precision using classical physics. The nucleus of an atom contains more than 99.94% of its mass. The electric charges of the protons are positive, those of the electrons are negative, and those of the neutrons are zero. The atom is electrically neutral if the number of protons and electrons is equal.

An atom has an overall charge of positive or negative if it contains more electrons than protons. These atoms are known as ions. The electromagnetic force pulls an atom's electrons towards the protons in its atomic nucleus. The nuclear force draws the protons and neutrons in the nucleus together. The electromagnetic force that keeps positively charged protons apart is typically weaker than this force. The electromagnetic force that repels objects can occasionally outweigh the nuclear force. The nucleus breaks in this instance, leaving behind several parts.

This type of nuclear decay exists. Atoms can create chemical compounds like molecules or crystals by joining up with one or more other atoms through chemical bonds. The majority of the physical changes seen in nature are caused by atoms' capacity to bind and detach. The science that investigates these changes is chemistry. The fundamental notion that matter is composed of tiny, inseparable particles is an old one that has roots in numerous ancient cultures. Atomos, which meaning "uncuttable" in ancient Greek, is the root of the word atom.

Rather than being founded on empirical evidence, this ancient concept was based on philosophical reasoning. These antiquated ideas are not the foundation of modern atomic physics. John Dalton, a scientist who lived in the early 19th century, observed that chemical elements appeared to join with one another in distinct weight units. He chose the term "atom" to describe these units since he believed those to be the basic building blocks of matter. Although it was later found that Dalton's atoms are not truly indivisible, the phrase persisted. 

John Dalton, an English chemist, discovered the "law of multiple proportions" in the early 1800s after compiling experimental data obtained by himself and other researchers. He observed that when a certain chemical element is present in chemical compounds, its weight will vary in these compounds by ratios of small whole numbers. As a result of this pattern, Dalton came to the conclusion that each chemical element interacts with other chemical elements through a fundamental unit of weight, which he named "atoms". 

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Some compounds, it was found by scientists, have the exact same chemical composition but different properties. For instance, Friedrich Wöhler found in 1827 that silver fulminate and silver cyanate have the same chemical composition of 107 parts silver, 12 parts carbon, 14 parts nitrogen, and 12 parts oxygen ( today known as AgCNO ). Isomerism was first used to characterise the phenomenon in 1830 by Jöns Jacob Berzelius. Louis Pasteur postulated in 1860 that molecules in isomers can share the same composition but have distinct atom configurations. 

The idea that the carbon atom forms a tetrahedral link with other atoms was first out by Jacobus Henricus van 't Hoff in 1874. From there, he developed an explanation of organic molecule structure that allowed him to forecast the number of isomers a drug may have. Pentane (C5H12) is a good illustration. Pentane has three potential configurations according to van 't Hoff's method of modelling molecules, and researchers later found three compounds with the same chemical make - up as pentane. 

British botanist Robert Brown first noticed the erratic motion of dust particles inside pollen grains floating in water in 1827. Albert Einstein proposed a mathematical model in 1905 to explain the Brownian motion, which he theorised was the result of water molecules continuously bouncing the grains around. French physicist Jean Perrin utilised Einstein's equation to determine the number of atoms in a mole and the size of atoms in order to experimentally test this hypothesis in 1908. 

Since cathode rays can be deflected by electrical and magnetic forces, J. J. Thomson revealed in 1897 that they are not electromagnetic waves but rather particles. These particles, according to his measurements, are 1,800 times lighter than hydrogen, the lightest atom. Thomson came to the conclusion that these particles, which were subatomic in nature, originated from the atoms inside the cathode. He gave these new particles the name corpuscles, but electrons eventually replaced that term.

Thomson also demonstrated that the particles emitted by photoelectric and radioactive materials were identical to electrons. The fact that electrons are the particles that conduct electric currents in metal wires was immediately established. Atoms are not indivisible, as Dalton believed, according to Thomson, who came to the conclusion that these electrons originated from the same atoms of the cathode in his instruments. ​According to J. J. Thomson, the positively charged electrons were dispersed throughout the atom's whole volume in a sea of positively charged ions.

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