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99-439: Silicon dioxide , also known as silica , is an oxide of silicon with the chemical formula SiO 2 , commonly found in nature as quartz . In many parts of the world, silica is the major constituent of sand . Silica is one of the most complex and abundant families of materials , existing as a compound of several minerals and as a synthetic product. Examples include fused quartz , fumed silica , opal , and aerogels . It

198-420: A bond dipole moment points from each H to the O, making the oxygen partially negative and each hydrogen partially positive. A large molecular dipole , points from a region between the two hydrogen atoms to the oxygen atom. The charge differences cause water molecules to aggregate (the relatively positive areas being attracted to the relatively negative areas). This attraction, hydrogen bonding , explains many of

297-435: A blue color. This can easily be observed in a water-filled bath or wash-basin whose lining is white. Large ice crystals, as in glaciers , also appear blue. Under standard conditions , water is primarily a liquid, unlike other analogous hydrides of the oxygen family , which are generally gaseous. This unique property of water is due to hydrogen bonding . The molecules of water are constantly moving concerning each other, and

396-468: A carrier gas at 200–500 °C. Silicon dioxide is a relatively inert material (hence its widespread occurrence as a mineral). Silica is often used as inert containers for chemical reactions. At high temperatures, it is converted to silicon by reduction with carbon. Oxide Oxides are extraordinarily diverse in terms of stoichiometries (the measurable relationship between reactants and chemical equations of an equation or reaction) and in terms of

495-419: A chemical reagent. A common and cheap reducing agent is carbon in the form of coke . The most prominent example is that of iron ore smelting . Many reactions are involved, but the simplified equation is usually shown as: Some metal oxides dissolve in the presence of reducing agents, which can include organic compounds. Reductive dissolution of ferric oxides is integral to geochemical phenomena such as

594-432: A deficiency of oxygen, the monoxide is produced: With excess oxygen, the dioxide is the product, the pathway proceeds by the intermediacy of carbon monoxide: Elemental nitrogen ( N 2 ) is difficult to convert to oxides, but the combustion of ammonia gives nitric oxide, which further reacts with oxygen: These reactions are practiced in the production of nitric acid , a commodity chemical. The chemical produced on

693-589: A denser molecular packing in which some of the lattice cavities are filled by water molecules. Above 4 °C, however, thermal expansion becomes the dominant effect, and water near the boiling point (100 °C) is about 4% less dense than water at 4 °C (39 °F). Under increasing pressure, ice undergoes a number of transitions to other polymorphs with higher density than liquid water, such as ice II , ice III , high-density amorphous ice (HDA), and very-high-density amorphous ice (VHDA). The unusual density curve and lower density of ice than of water

792-430: A few noble gases. The pathways for the formation of this diverse family of compounds are correspondingly numerous. Many metal oxides arise by decomposition of other metal compounds, e.g. carbonates, hydroxides, and nitrates. In the making of calcium oxide, calcium carbonate (limestone) breaks down upon heating, releasing carbon dioxide: The reaction of elements with oxygen in air is a key step in corrosion relevant to

891-405: A glass with no true melting point, can be used as a glass fibre for fibreglass. Silicon dioxide is mostly obtained by mining, including sand mining and purification of quartz . Quartz is suitable for many purposes, while chemical processing is required to make a purer or otherwise more suitable (e.g. more reactive or fine-grained) product. Precipitated silica or amorphous silica is produced by

990-490: A heat capacity minimum. Its density decreases from 2.08 g/cm at 1950 °C to 2.03 g/cm at 2200 °C. The molecular SiO 2 has a linear structure like CO 2 . It has been produced by combining silicon monoxide (SiO) with oxygen in an argon matrix. The dimeric silicon dioxide, (SiO 2 ) 2 has been obtained by reacting O 2 with matrix isolated dimeric silicon monoxide, (Si 2 O 2 ). In dimeric silicon dioxide there are two oxygen atoms bridging between

1089-488: A high heat of vaporization (40.65 kJ/mol or 2257 kJ/kg at the normal boiling point), both of which are a result of the extensive hydrogen bonding between its molecules. These two unusual properties allow water to moderate Earth's climate by buffering large fluctuations in temperature. Most of the additional energy stored in the climate system since 1970 has accumulated in the oceans . The specific enthalpy of fusion (more commonly known as latent heat) of water

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1188-449: A low value of 140° in α-tridymite, up to 180° in β-tridymite. In α-quartz, the Si–O–Si angle is 144°. Alpha quartz is the most stable form of solid SiO 2 at room temperature. The high-temperature minerals, cristobalite and tridymite, have both lower densities and indices of refraction than quartz. The transformation from α-quartz to beta-quartz takes place abruptly at 573 °C. Since

1287-487: A sample of liquid water, a large portion of the molecules are held together by such bonds. Water also has high adhesion properties because of its polar nature. On clean, smooth glass the water may form a thin film because the molecular forces between glass and water molecules (adhesive forces) are stronger than the cohesive forces. In biological cells and organelles , water is in contact with membrane and protein surfaces that are hydrophilic ; that is, surfaces that have

1386-408: A silicon wafer enables it to overcome the surface states that otherwise prevent electricity from reaching the semiconducting layer. The process of silicon surface passivation by thermal oxidation (silicon dioxide) is critical to the semiconductor industry . It is commonly used to manufacture metal–oxide–semiconductor field-effect transistors (MOSFETs) and silicon integrated circuit chips (with

1485-434: A solid form less dense than its liquid form, a relatively high boiling point of 100 °C for its molar mass , and a high heat capacity . Water is amphoteric , meaning that it can exhibit properties of an acid or a base , depending on the pH of the solution that it is in; it readily produces both H and OH ions. Related to its amphoteric character, it undergoes self-ionization . The product of

1584-577: A strong attraction to water. Irving Langmuir observed a strong repulsive force between hydrophilic surfaces. To dehydrate hydrophilic surfaces—to remove the strongly held layers of water of hydration—requires doing substantial work against these forces, called hydration forces. These forces are very large but decrease rapidly over a nanometer or less. They are important in biology, particularly when cells are dehydrated by exposure to dry atmospheres or to extracellular freezing. Water has an unusually high surface tension of 71.99 mN/m at 25 °C which

1683-433: A substance to dissolve in water is determined by whether or not the substance can match or better the strong attractive forces that water molecules generate between other water molecules. If a substance has properties that do not allow it to overcome these strong intermolecular forces, the molecules are precipitated out from the water. Contrary to the common misconception, water and hydrophobic substances do not "repel", and

1782-430: A value of about 10 at 25 °C. At neutral pH , the concentration of the hydroxide ion ( OH ) equals that of the (solvated) hydrogen ion ( H ), with a value close to 10 mol L at 25 °C. See data page for values at other temperatures. The thermodynamic equilibrium constant is a quotient of thermodynamic activities of all products and reactants including water: However, for dilute solutions,

1881-474: A very shallow layer of about 1 nm or 10 Å of so-called native oxide. Higher temperatures and alternative environments are used to grow well-controlled layers of silicon dioxide on silicon, for example at temperatures between 600 and 1200 °C, using so-called dry oxidation with O 2 or wet oxidation with H 2 O. The native oxide layer is beneficial in microelectronics , where it acts as electric insulator with high chemical stability. It can protect

1980-447: A very slight electrical conductivity of 0.05501 ± 0.0001 μS / cm at 25.00 °C. Water can also be electrolyzed into oxygen and hydrogen gases but in the absence of dissolved ions this is a very slow process, as very little current is conducted. In ice, the primary charge carriers are protons (see proton conductor ). Ice was previously thought to have a small but measurable conductivity of 1 × 10  S/cm, but this conductivity

2079-522: A white powder with extremely low bulk density (0.03-0.15 g/cm) and thus high surface area. The particles act as a thixotropic thickening agent, or as an anti-caking agent, and can be treated to make them hydrophilic or hydrophobic for either water or organic liquid applications. Silica fume is an ultrafine powder collected as a by-product of the silicon and ferrosilicon alloy production. It consists of amorphous (non-crystalline) spherical particles with an average particle diameter of 150 nm, without

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2178-476: Is table salt ; the sodium chloride, NaCl, separates into Na cations and Cl anions , each being surrounded by water molecules. The ions are then easily transported away from their crystalline lattice into solution. An example of a nonionic solute is table sugar . The water dipoles make hydrogen bonds with the polar regions of the sugar molecule (OH groups) and allow it to be carried away into solution. The quantum tunneling dynamics in water

2277-460: Is 104.48°, which is smaller than the typical tetrahedral angle of 109.47°. The lone pairs are closer to the oxygen atom than the electrons sigma bonded to the hydrogens, so they require more space. The increased repulsion of the lone pairs forces the O–H bonds closer to each other. Another consequence of its structure is that water is a polar molecule . Due to the difference in electronegativity ,

2376-401: Is 333.55 kJ/kg at 0 °C: the same amount of energy is required to melt ice as to warm ice from −160 °C up to its melting point or to heat the same amount of water by about 80 °C. Of common substances, only that of ammonia is higher. This property confers resistance to melting on the ice of glaciers and drift ice . Before and since the advent of mechanical refrigeration , ice

2475-636: Is a triple point of water. Since 1954, this point had been used to define the base unit of temperature, the kelvin , but, starting in 2019 , the kelvin is now defined using the Boltzmann constant , rather than the triple point of water. Due to the existence of many polymorphs (forms) of ice, water has other triple points, which have either three polymorphs of ice or two polymorphs of ice and liquid in equilibrium. Gustav Heinrich Johann Apollon Tammann in Göttingen produced data on several other triple points in

2574-554: Is a gas at room temperature , despite hydrogen sulfide having nearly twice the molar mass of water. The extra bonding between water molecules also gives liquid water a large specific heat capacity . This high heat capacity makes water a good heat storage medium (coolant) and heat shield. Water molecules stay close to each other ( cohesion ), due to the collective action of hydrogen bonds between water molecules. These hydrogen bonds are constantly breaking, with new bonds being formed with different water molecules; but at any given time in

2673-520: Is a more complex molecular oxide with a deceptive name, the real formula being P 4 O 10 . Tetroxides are rare, with a few more common examples being ruthenium tetroxide , osmium tetroxide , and xenon tetroxide . Reduction of metal oxide to the metal is practiced on a large scale in the production of some metals. Many metal oxides convert to metals simply by heating, (see Thermal decomposition ). For example, silver oxide decomposes at 200 °C: Most often, however, metals oxides are reduced by

2772-421: Is also less dense than liquid water—upon freezing, the density of water decreases by about 9%. These peculiar effects are due to the highly directional bonding of water molecules via the hydrogen bonds: ice and liquid water at low temperature have comparatively low-density, low-energy open lattice structures. The breaking of hydrogen bonds on melting with increasing temperature in the range 0–4 °C allows for

2871-437: Is also the primary component of rice husk ash , which is used, for example, in filtration and as supplementary cementitious material (SCM) in cement and concrete manufacturing. Silicification in and by cells has been common in the biological world and it occurs in bacteria, protists, plants, and animals (invertebrates and vertebrates). Prominent examples include: About 95% of the commercial use of silicon dioxide (sand)

2970-504: Is an excellent electronic insulator , but not even "deionized" water is completely free of ions. Water undergoes autoionization in the liquid state when two water molecules form one hydroxide anion ( OH ) and one hydronium cation ( H 3 O ). Because of autoionization, at ambient temperatures pure liquid water has a similar intrinsic charge carrier concentration to the semiconductor germanium and an intrinsic charge carrier concentration three orders of magnitude greater than

3069-677: Is by far the most studied chemical compound and is described as the "universal solvent " and the "solvent of life". It is the most abundant substance on the surface of Earth and the only common substance to exist as a solid , liquid, and gas on Earth's surface. It is also the third most abundant molecule in the universe (behind molecular hydrogen and carbon monoxide ). Water molecules form hydrogen bonds with each other and are strongly polar. This polarity allows it to dissociate ions in salts and bond to other polar substances such as alcohols and acids, thus dissolving them. Its hydrogen bonding causes its many unique properties, such as having

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3168-446: Is called supersaturated and can occur if the air is rapidly cooled, for example, by rising suddenly in an updraft. The compressibility of water is a function of pressure and temperature. At 0 °C, at the limit of zero pressure, the compressibility is 5.1 × 10  Pa . At the zero-pressure limit, the compressibility reaches a minimum of 4.4 × 10  Pa around 45 °C before increasing again with increasing temperature. As

3267-602: Is caused by the strength of the hydrogen bonding between water molecules. This allows insects to walk on water. Because water has strong cohesive and adhesive forces, it exhibits capillary action. Strong cohesion from hydrogen bonding and adhesion allows trees to transport water more than 100 m upward. Water is an excellent solvent due to its high dielectric constant. Substances that mix well and dissolve in water are known as hydrophilic ("water-loving") substances, while those that do not mix well with water are known as hydrophobic ("water-fearing") substances. The ability of

3366-601: Is covalently bonded in a tetrahedral manner to 4 oxygen atoms. In contrast, CO 2 is a linear molecule. The starkly different structures of the dioxides of carbon and silicon are a manifestation of the double bond rule . Based on the crystal structural differences, silicon dioxide can be divided into two categories: crystalline and non-crystalline (amorphous). In crystalline form, this substance can be found naturally occurring as quartz , tridymite (high-temperature form), cristobalite (high-temperature form), stishovite (high-pressure form), and coesite (high-pressure form). On

3465-435: Is essential for much of the life on earth—if water were most dense at the freezing point, then in winter the cooling at the surface would lead to convective mixing. Once 0 °C are reached, the water body would freeze from the bottom up, and all life in it would be killed. Furthermore, given that water is a good thermal insulator (due to its heat capacity), some frozen lakes might not completely thaw in summer. As it is,

3564-463: Is in the construction industry, e.g. in the production of concrete ( Portland cement concrete ). Certain deposits of silica sand, with desirable particle size and shape and desirable clay and other mineral content, were important for sand casting of metallic products. The high melting point of silica enables it to be used in such applications such as iron casting; modern sand casting sometimes uses other minerals for other reasons. Crystalline silica

3663-415: Is known as ice and commonly takes the structure of hard, amalgamated crystals , such as ice cubes , or loosely accumulated granular crystals, like snow . Aside from common hexagonal crystalline ice , other crystalline and amorphous phases of ice are known. The gaseous phase of water is known as water vapor (or steam ). Visible steam and clouds are formed from minute droplets of water suspended in

3762-473: Is now thought to be almost entirely from surface defects, and without those, ice is an insulator with an immeasurably small conductivity. An important feature of water is its polar nature. The structure has a bent molecular geometry for the two hydrogens from the oxygen vertex. The oxygen atom also has two lone pairs of electrons. One effect usually ascribed to the lone pairs is that the H–O–H gas-phase bend angle

3861-649: Is obtained by the dealumination of a low-sodium, ultra-stable Y zeolite with combined acid and thermal treatment. The resulting product contains over 99% silica, and has high crystallinity and specific surface area (over 800 m/g). Faujasite-silica has very high thermal and acid stability. For example, it maintains a high degree of long-range molecular order or crystallinity even after boiling in concentrated hydrochloric acid . Molten silica exhibits several peculiar physical characteristics that are similar to those observed in liquid water : negative temperature expansion, density maximum at temperatures ~5000 °C, and

3960-427: Is only a 1.8% decrease in volume. The bulk modulus of water ice ranges from 11.3 GPa at 0 K up to 8.6 GPa at 273 K. The large change in the compressibility of ice as a function of temperature is the result of its relatively large thermal expansion coefficient compared to other common solids. The temperature and pressure at which ordinary solid, liquid, and gaseous water coexist in equilibrium

4059-419: Is rapidly cooled, it does not crystallize, but solidifies as a glass. Because of this, most ceramic glazes have silica as the main ingredient. The structural geometry of silicon and oxygen in glass is similar to that in quartz and most other crystalline forms of silicon and oxygen, with silicon surrounded by regular tetrahedra of oxygen centres. The difference between the glass and crystalline forms arises from

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4158-423: Is that the oxygen atom's lone pairs are physically larger and therefore take up more space than the oxygen atom's bonds to the hydrogen atoms. The molecular orbital theory explanation ( Bent's rule ) is that lowering the energy of the oxygen atom's nonbonding hybrid orbitals (by assigning them more s character and less p character) and correspondingly raising the energy of the oxygen atom's hybrid orbitals bonded to

4257-423: Is the major constituent of sand . Even though it is poorly soluble, silica occurs in many plants such as rice . Plant materials with high silica phytolith content appear to be of importance to grazing animals, from chewing insects to ungulates . Silica accelerates tooth wear, and high levels of silica in plants frequently eaten by herbivores may have developed as a defense mechanism against predation. Silica

4356-453: Is the only polymorph of silica stable at the Earth's surface. Metastable occurrences of the high-pressure forms coesite and stishovite have been found around impact structures and associated with eclogites formed during ultra-high-pressure metamorphism . The high-temperature forms of tridymite and cristobalite are known from silica-rich volcanic rocks . In many parts of the world, silica

4455-501: Is the process by which a semiconductor surface is rendered inert, and does not change semiconductor properties as a result of interaction with air or other materials in contact with the surface or edge of the crystal. The formation of a thermally grown silicon dioxide layer greatly reduces the concentration of electronic states at the silicon surface . SiO 2 films preserve the electrical characteristics of p–n junctions and prevent these electrical characteristics from deteriorating by

4554-401: Is thermodynamically stable with the liquid (or solid) at a given temperature is relatively low compared with total atmospheric pressure. For example, if the vapor's partial pressure is 2% of atmospheric pressure and the air is cooled from 25 °C, starting at about 22 °C, water will start to condense, defining the dew point , and creating fog or dew . The reverse process accounts for

4653-431: Is used as a fining agent for wine, beer, and juice, with the E number reference E551 . In cosmetics, silica is useful for its light-diffusing properties and natural absorbency. Diatomaceous earth , a mined product, has been used in food and cosmetics for centuries. It consists of the silica shells of microscopic diatoms ; in a less processed form it was sold as "tooth powder". Manufactured or mined hydrated silica

4752-486: Is used as the hard abrasive in toothpaste . Silicon dioxide is widely used in the semiconductor technology: Because silicon dioxide is a native oxide of silicon it is more widely used compared to other semiconductors like gallium arsenide or indium phosphide . Silicon dioxide could be grown on a silicon semiconductor surface. Silicon oxide layers could protect silicon surfaces during diffusion processes , and could be used for diffusion masking. Surface passivation

4851-416: Is used in hydraulic fracturing of formations which contain tight oil and shale gas . Silica is the primary ingredient in the production of most glass . As other minerals are melted with silica, the principle of freezing point depression lowers the melting point of the mixture and increases fluidity. The glass transition temperature of pure SiO 2 is about 1475 K. When molten silicon dioxide SiO 2

4950-498: Is used in structural materials , microelectronics , and as components in the food and pharmaceutical industries. All forms are white or colorless, although impure samples can be colored. Silicon dioxide is a common fundamental constituent of glass . In the majority of silicon dioxides, the silicon atom shows tetrahedral coordination , with four oxygen atoms surrounding a central Si atom ( see 3-D Unit Cell ). Thus, SiO 2 forms 3-dimensional network solids in which each silicon atom

5049-536: Is used to produce elemental silicon . The process involves carbothermic reduction in an electric arc furnace : Fumed silica , also known as pyrogenic silica, is prepared by burning SiCl 4 in an oxygen-rich hydrogen flame to produce a "smoke" of SiO 2 . It can also be produced by vaporizing quartz sand in a 3000 °C electric arc. Both processes result in microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles,

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5148-543: The activities , or approximately, the concentrations of H and OH is a constant, so their respective concentrations are inversely proportional to each other. Water is the chemical substance with chemical formula H 2 O ; one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom. Water is a tasteless, odorless liquid at ambient temperature and pressure . Liquid water has weak absorption bands at wavelengths of around 750 nm which cause it to appear to have

5247-683: The iron cycle . Because the M-O bonds are typically strong, metal oxides tend to be insoluble in solvents, though they may be attacked by aqueous acids and bases. Dissolution of oxides often gives oxyanions . Adding aqueous base to P 4 O 10 gives various phosphates . Adding aqueous base to MoO 3 gives polyoxometalates . Oxycations are rarer, some examples being nitrosonium ( NO ), vanadyl ( VO ), and uranyl ( UO 2+ 2 ). Of course many compounds are known with both oxides and other groups. In organic chemistry , these include ketones and many related carbonyl compounds. For

5346-545: The planar process ). Hydrophobic silica is used as a defoamer component . In its capacity as a refractory , it is useful in fiber form as a high-temperature thermal protection fabric. Silica is used in the extraction of DNA and RNA due to its ability to bind to the nucleic acids under the presence of chaotropes . Silica aerogel was used in the Stardust spacecraft to collect extraterrestrial particles. Pure silica (silicon dioxide), when cooled as fused quartz into

5445-474: The string theory of physics) was coined. These observations were based upon X-ray absorption spectroscopy that probed the local environment of individual oxygen atoms. The repulsive effects of the two lone pairs on the oxygen atom cause water to have a bent , not linear , molecular structure, allowing it to be polar. The hydrogen–oxygen–hydrogen angle is 104.45°, which is less than the 109.47° for ideal sp hybridization . The valence bond theory explanation

5544-494: The acidification of solutions of sodium silicate . The gelatinous precipitate or silica gel , is first washed and then dehydrated to produce colorless microporous silica. The idealized equation involving a trisilicate and sulfuric acid is: Approximately one billion kilograms/year (1999) of silica were produced in this manner, mainly for use for polymer composites – tires and shoe soles. Thin films of silica grow spontaneously on silicon wafers via thermal oxidation , producing

5643-410: The air is at equilibrium with vapor pressure due to (liquid) water; water (or ice, if cool enough) will fail to lose mass through evaporation when exposed to saturated air. Because the amount of water vapor in the air is small, relative humidity, the ratio of the partial pressure due to the water vapor to the saturated partial vapor pressure, is much more useful. Vapor pressure above 100% relative humidity

5742-403: The air. Water also forms a supercritical fluid . The critical temperature is 647 K and the critical pressure is 22.064 MPa . In nature, this only rarely occurs in extremely hostile conditions. A likely example of naturally occurring supercritical water is in the hottest parts of deep water hydrothermal vents , in which water is heated to the critical temperature by volcanic plumes and

5841-550: The branching of the pyrogenic product. The main use is as pozzolanic material for high performance concrete. Fumed silica nanoparticles can be successfully used as an anti-aging agent in asphalt binders. Silica, either colloidal, precipitated, or pyrogenic fumed, is a common additive in food production. It is used primarily as a flow or anti- caking agent in powdered foods such as spices and non-dairy coffee creamer, or powders to be formed into pharmaceutical tablets. It can adsorb water in hygroscopic applications. Colloidal silica

5940-608: The cathode in electrolysis) or other anions (a negatively charged ion). Iron silicate , Fe 2 SiO 4 , the mineral fayalite , is one of many examples of a ternary oxide. For many metal oxides, the possibilities of polymorphism and nonstoichiometry exist as well. The commercially important dioxides of titanium exists in three distinct structures, for example. Many metal oxides exist in various nonstoichiometric states. Many molecular oxides exist with diverse ligands as well. For simplicity sake, most of this article focuses on binary oxides. Oxides are associated with all elements except

6039-727: The commercial use of iron especially. Almost all elements form oxides upon heating with oxygen atmosphere. For example, zinc powder will burn in air to give zinc oxide: The production of metals from ores often involves the production of oxides by roasting (heating) metal sulfide minerals in air. In this way, MoS 2 ( molybdenite ) is converted to molybdenum trioxide , the precursor to virtually all molybdenum compounds: Noble metals (such as gold and platinum ) are prized because they resist direct chemical combination with oxygen. Important and prevalent nonmetal oxides are carbon dioxide and carbon monoxide . These species form upon full or partial oxidation of carbon or hydrocarbons. With

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6138-505: The connectivity of the tetrahedral units: Although there is no long-range periodicity in the glassy network, ordering remains at length scales well beyond the SiO bond length. One example of this ordering is the preference to form rings of 6-tetrahedra. The majority of optical fibers for telecommunications are also made from silica. It is a primary raw material for many ceramics such as earthenware , stoneware , and porcelain . Silicon dioxide

6237-468: The contribution coming from the hydrogen atoms' 1s orbitals). In liquid water there is some self-ionization giving hydronium ions and hydroxide ions. The equilibrium constant for this reaction, known as the ionic product of water, K w = [ H 3 O + ] [ O H − ] {\displaystyle K_{\rm {w}}=[{\rm {H_{3}O^{+}}}][{\rm {OH^{-}}}]} , has

6336-431: The critical pressure is caused by the weight of the ocean at the extreme depths where the vents are located. This pressure is reached at a depth of about 2200 meters: much less than the mean depth of the ocean (3800 meters). Water has a very high specific heat capacity of 4184 J/(kg·K) at 20 °C (4182 J/(kg·K) at 25 °C) —the second-highest among all the heteroatomic species (after ammonia ), as well as

6435-484: The densest of the low-pressure forms, which has a density of 2.648 g/cm. The difference in density can be ascribed to the increase in coordination as the six shortest Si–O bond lengths in stishovite (four Si–O bond lengths of 176 pm and two others of 181 pm) are greater than the Si–O bond length (161 pm) in α-quartz. The change in the coordination increases the ionicity of the Si–O bond. Faujasite silica, another polymorph,

6534-420: The dissolved salt content as well as the temperature. Ice still floats in the oceans, otherwise, they would freeze from the bottom up. However, the salt content of oceans lowers the freezing point by about 1.9 °C (due to freezing-point depression of a solvent containing a solute ) and lowers the temperature of the density maximum of water to the former freezing point at 0 °C. This is why, in ocean water,

6633-535: The downward convection of colder water is not blocked by an expansion of water as it becomes colder near the freezing point. The oceans' cold water near the freezing point continues to sink. So creatures that live at the bottom of cold oceans like the Arctic Ocean generally live in water 4 °C colder than at the bottom of frozen-over fresh water lakes and rivers. As the surface of saltwater begins to freeze (at −1.9 °C for normal salinity seawater , 3.5%)

6732-617: The early 20th century. Kamb and others documented further triple points in the 1960s. The melting point of ice is 0 °C (32 °F; 273 K) at standard pressure; however, pure liquid water can be supercooled well below that temperature without freezing if the liquid is not mechanically disturbed. It can remain in a fluid state down to its homogeneous nucleation point of about 231 K (−42 °C; −44 °F). The melting point of ordinary hexagonal ice falls slightly under moderately high pressures, by 0.0073 °C (0.0131 °F)/atm or about 0.5 °C (0.90 °F)/70 atm as

6831-400: The fog burning off in the morning. If the humidity is increased at room temperature, for example, by running a hot shower or a bath, and the temperature stays about the same, the vapor soon reaches the pressure for phase change and then condenses out as minute water droplets, commonly referred to as steam. A saturated gas or one with 100% relative humidity is when the vapor pressure of water in

6930-400: The four hydrogen bonds, thereby forming an open structure and a three-dimensional bonding network, resulting in the anomalous decrease in density when cooled below 4 °C. This repeated, constantly reorganizing unit defines a three-dimensional network extending throughout the liquid. This view is based upon neutron scattering studies and computer simulations, and it makes sense in the light of

7029-409: The gaseous ambient environment. Silicon oxide layers could be used to electrically stabilize silicon surfaces. The surface passivation process is an important method of semiconductor device fabrication that involves coating a silicon wafer with an insulating layer of silicon oxide so that electricity could reliably penetrate to the conducting silicon below. Growing a layer of silicon dioxide on top of

7128-409: The highest oxidation state oxide is copper(II) oxide and not copper(I) oxide . Another exception is fluoride , which does not exist as one might expect—as F 2 O 7 —but as OF 2 . Water (properties) Water ( H 2 O ) is a polar inorganic compound that is at room temperature a tasteless and odorless liquid , which is nearly colorless apart from an inherent hint of blue . It

7227-413: The hydration of a hydrophobic surface is energetically, but not entropically, favorable. When an ionic or polar compound enters water, it is surrounded by water molecules ( hydration ). The relatively small size of water molecules (~ 3 angstroms) allows many water molecules to surround one molecule of solute . The partially negative dipole ends of the water are attracted to positively charged components of

7326-436: The hydrogen atoms (by assigning them more p character and less s character) has the net effect of lowering the energy of the occupied molecular orbitals because the energy of the oxygen atom's nonbonding hybrid orbitals contributes completely to the energy of the oxygen atom's lone pairs while the energy of the oxygen atom's other two hybrid orbitals contributes only partially to the energy of the bonding orbitals (the remainder of

7425-434: The hydrogen bonds are continually breaking and reforming at timescales faster than 200 femtoseconds (2 × 10 seconds). However, these bonds are strong enough to create many of the peculiar properties of water, some of which make it integral to life. Within the Earth's atmosphere and surface, the liquid phase is the most common and is the form that is generally denoted by the word "water". The solid phase of water

7524-428: The ice that forms is essentially salt-free, with about the same density as freshwater ice. This ice floats on the surface, and the salt that is "frozen out" adds to the salinity and density of the seawater just below it, in a process known as brine rejection . This denser saltwater sinks by convection and the replacing seawater is subject to the same process. This produces essentially freshwater ice at −1.9 °C on

7623-456: The inversion of the density curve leads to a stable layering for surface temperatures below 4 °C, and with the layer of ice that floats on top insulating the water below, even e.g., Lake Baikal in central Siberia freezes only to about 1 m thickness in winter. In general, for deep enough lakes, the temperature at the bottom stays constant at about 4 °C (39 °F) throughout the year (see diagram). The density of saltwater depends on

7722-777: The largest scale industrially is sulfuric acid . It is produced by the oxidation of sulfur to sulfur dioxide , which is separately oxidized to sulfur trioxide : Finally the trioxide is converted to sulfuric acid by a hydration reaction : Oxides have a range of structures, from individual molecules to polymeric and crystalline structures. At standard conditions, oxides may range from solids to gases. Solid oxides of metals usually have polymeric structures at ambient conditions. Although most metal oxides are crystalline solids, many non-metal oxides are molecules. Examples of molecular oxides are carbon dioxide and carbon monoxide . All simple oxides of nitrogen are molecular, e.g., NO, N 2 O, NO 2 and N 2 O 4 . Phosphorus pentoxide

7821-399: The other hand, amorphous silica can be found in nature as opal and diatomaceous earth . Quartz glass is a form of intermediate state between these structures. All of these distinct crystalline forms always have the same local structure around Si and O. In α-quartz the Si–O bond length is 161 pm, whereas in α-tridymite it is in the range 154–171 pm. The Si–O–Si angle also varies between

7920-440: The pressure is increased, the compressibility decreases, being 3.9 × 10  Pa at 0 °C and 100 megapascals (1,000 bar). The bulk modulus of water is about 2.2 GPa. The low compressibility of non-gasses, and of water in particular, leads to their often being assumed as incompressible. The low compressibility of water means that even in the deep oceans at 4 km depth, where pressures are 40 MPa, there

8019-546: The properties of water, such as its solvent properties. Although hydrogen bonding is a relatively weak attraction compared to the covalent bonds within the water molecule itself, it is responsible for several of the water's physical properties. These properties include its relatively high melting and boiling point temperatures: more energy is required to break the hydrogen bonds between water molecules. In contrast, hydrogen sulfide ( H 2 S ), has much weaker hydrogen bonding due to sulfur's lower electronegativity. H 2 S

8118-482: The same year, the discovery of the quantum tunneling of water molecules was reported. Water is relatively transparent to visible light , near ultraviolet light, and far-red light, but it absorbs most ultraviolet light , infrared light , and microwaves . Most photoreceptors and photosynthetic pigments utilize the portion of the light spectrum that is transmitted well through water. Microwave ovens take advantage of water's opacity to microwave radiation to heat

8217-429: The semiconductor silicon, hence, based on charge carrier concentration, water can not be considered to be a completely dielectric material or electrical insulator but to be a limited conductor of ionic charge. Because water is such a good solvent, it almost always has some solute dissolved in it, often a salt . If water has even a tiny amount of such an impurity, then the ions can carry charges back and forth, allowing

8316-399: The silicon atoms with an Si–O–Si angle of 94° and bond length of 164.6 pm and the terminal Si–O bond length is 150.2 pm. The Si–O bond length is 148.3 pm, which compares with the length of 161 pm in α-quartz. The bond energy is estimated at 621.7 kJ/mol. SiO 2 is most commonly encountered in nature as quartz , which comprises more than 10% by mass of the Earth's crust. Quartz

8415-415: The silicon, store charge, block current, and even act as a controlled pathway to limit current flow. Many routes to silicon dioxide start with an organosilicon compound, e.g., HMDSO, TEOS. Synthesis of silica is illustrated below using tetraethyl orthosilicate (TEOS). Simply heating TEOS at 680–730 °C results in the oxide: Similarly TEOS combusts around 400 °C: TEOS undergoes hydrolysis via

8514-491: The so-called sol-gel process . The course of the reaction and nature of the product are affected by catalysts, but the idealized equation is: Being highly stable, silicon dioxide arises from many methods. Conceptually simple, but of little practical value, combustion of silane gives silicon dioxide. This reaction is analogous to the combustion of methane: However the chemical vapor deposition of silicon dioxide onto crystal surface from silane had been used using nitrogen as

8613-471: The solute, and vice versa for the positive dipole ends. In general, ionic and polar substances such as acids , alcohols , and salts are relatively soluble in water, and nonpolar substances such as fats and oils are not. Nonpolar molecules stay together in water because it is energetically more favorable for the water molecules to hydrogen bond to each other than to engage in van der Waals interactions with non-polar molecules. An example of an ionic solute

8712-402: The stabilization energy of hydrogen bonding is exceeded by intermolecular repulsion, but as ice transforms into its polymorphs (see crystalline states of ice ) above 209.9 MPa (2,072 atm), the melting point increases markedly with pressure , i.e., reaching 355 K (82 °C) at 2.216 GPa (21,870 atm) (triple point of Ice VII ). Pure water containing no exogenous ions

8811-462: The structures of each stoichiometry. Most elements form oxides of more than one stoichiometry. A well known example is carbon monoxide and carbon dioxide . This applies to binary oxides, that is, compounds containing only oxide and another element. Far more common than binary oxides are oxides of more complex stoichiometries. Such complexity can arise by the introduction of other cations (a positively charged ion, i.e. one that would be attracted to

8910-574: The surface. The increased density of the seawater beneath the forming ice causes it to sink towards the bottom. On a large scale, the process of brine rejection and sinking cold salty water results in ocean currents forming to transport such water away from the Poles, leading to a global system of currents called the thermohaline circulation . Water is miscible with many liquids, including ethanol in all proportions. Water and most oils are immiscible, usually forming layers according to increasing density from

9009-444: The temperature increases, the density rises to a peak at 3.98 °C (39.16 °F) and then decreases; the initial increase is unusual because most liquids undergo thermal expansion so that the density only decreases as a function of temperature. The increase observed for water from 0 °C (32 °F) to 3.98 °C (39.16 °F) and for a few other liquids is described as negative thermal expansion . Regular, hexagonal ice

9108-412: The top. This can be predicted by comparing the polarity . Water being a relatively polar compound will tend to be miscible with liquids of high polarity such as ethanol and acetone, whereas compounds with low polarity will tend to be immiscible and poorly soluble such as with hydrocarbons . As a gas, water vapor is completely miscible with air. On the other hand, the maximum water vapor pressure that

9207-443: The transformation is accompanied by a significant change in volume, it can easily induce fracturing of ceramics or rocks passing through this temperature limit. The high-pressure minerals, seifertite , stishovite, and coesite, though, have higher densities and indices of refraction than quartz. Stishovite has a rutile -like structure where silicon is 6-coordinate. The density of stishovite is 4.287 g/cm, which compares to α-quartz,

9306-399: The transition metals, many oxo complexes are known as well as oxyhalides . The chemical formulas of the oxides of the chemical elements in their highest oxidation state are predictable and are derived from the number of valence electrons for that element. Even the chemical formula of O 4 , tetraoxygen , is predictable as a group 16 element . One exception is copper , for which

9405-406: The unambiguously tetrahedral arrangement of water molecules in ice structures. However, there is an alternative theory for the structure of water. In 2004, a controversial paper from Stockholm University suggested that water molecules in the liquid state typically bind not to four but only two others; thus forming chains and rings. The term "string theory of water" (which is not to be confused with

9504-729: The water inside of foods. Water's light blue color is caused by weak absorption in the red part of the visible spectrum . A single water molecule can participate in a maximum of four hydrogen bonds because it can accept two bonds using the lone pairs on oxygen and donate two hydrogen atoms. Other molecules like hydrogen fluoride , ammonia, and methanol can also form hydrogen bonds. However, they do not show anomalous thermodynamic , kinetic , or structural properties like those observed in water because none of them can form four hydrogen bonds: either they cannot donate or accept hydrogen atoms, or there are steric effects in bulky residues. In water, intermolecular tetrahedral structures form due to

9603-594: The water to conduct electricity far more readily. It is known that the theoretical maximum electrical resistivity for water is approximately 18.2 MΩ·cm (182 kΩ ·m) at 25 °C. This figure agrees well with what is typically seen on reverse osmosis , ultra-filtered and deionized ultra-pure water systems used, for instance, in semiconductor manufacturing plants. A salt or acid contaminant level exceeding even 100 parts per trillion (ppt) in otherwise ultra-pure water begins to noticeably lower its resistivity by up to several kΩ·m. In pure water, sensitive equipment can detect

9702-407: Was and still is in common use for retarding food spoilage. The specific heat capacity of ice at −10 °C is 2030 J/(kg·K) and the heat capacity of steam at 100 °C is 2080 J/(kg·K). The density of water is about 1 gram per cubic centimetre (62 lb/cu ft): this relationship was originally used to define the gram. The density varies with temperature, but not linearly: as

9801-434: Was reported as early as 1992. At that time it was known that there are motions which destroy and regenerate the weak hydrogen bond by internal rotations of the substituent water monomers . On 18 March 2016, it was reported that the hydrogen bond can be broken by quantum tunneling in the water hexamer . Unlike previously reported tunneling motions in water, this involved the concerted breaking of two hydrogen bonds. Later in

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