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97-507: An ice piedmont consists of " Ice covering a coastal strip of low-lying land backed by mountains ." This article related to topography is a stub . You can help Misplaced Pages by expanding it . Ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C , 32 ° F , or 273.15 K . It occurs naturally on Earth , on other planets, in Oort cloud objects, and as interstellar ice . As

194-403: A linear combination of atomic orbitals is performed first, followed by filling of the resulting molecular orbitals with electrons. The two approaches are regarded as complementary, and each provides its own insights into the problem of chemical bonding. As valence bond theory builds the molecular wavefunction out of localized bonds, it is more suited for the calculation of bond energies and

291-619: A density between a quarter and two thirds that of pure ice, due to a high proportion of trapped air, which also makes soft rime appear white. Hard rime is denser, more transparent, and more likely to appear on ships and aircraft. Cold wind specifically causes what is known as advection frost when it collides with objects. When it occurs on plants, it often causes damage to them. Various methods exist to protect agricultural crops from frost - from simply covering them to using wind machines. In recent decades, irrigation sprinklers have been calibrated to spray just enough water to preemptively create

388-410: A few molecules in the droplet need to get together by chance to form an arrangement similar to that in an ice lattice; then the droplet freezes around this "nucleus". Experiments show that this "homogeneous" nucleation of cloud droplets only occurs at temperatures lower than −35 °C (238 K; −31 °F). In warmer clouds an aerosol particle or "ice nucleus" must be present in (or in contact with)

485-704: A form of precipitation consisting of small, translucent balls of ice, which are usually smaller than hailstones. This form of precipitation is also referred to as "sleet" by the United States National Weather Service . (In British English "sleet" refers to a mixture of rain and snow .) Ice pellets typically form alongside freezing rain, when a wet warm front ends up between colder and drier atmospheric layers. There, raindrops would both freeze and shrink in size due to evaporative cooling. So-called snow pellets, or graupel , form when multiple water droplets freeze onto snowflakes until

582-442: A full (or closed) outer electron shell. In the diagram of methane shown here, the carbon atom has a valence of four and is, therefore, surrounded by eight electrons (the octet rule ), four from the carbon itself and four from the hydrogens bonded to it. Each hydrogen has a valence of one and is surrounded by two electrons (a duet rule) – its own one electron plus one from the carbon. The numbers of electrons correspond to full shells in

679-559: A function of temperature and sliding speed. 2014 research suggests that frictional heating is the most important process under most typical conditions. The term that collectively describes all of the parts of the Earth's surface where water is in frozen form is the cryosphere . Ice is an important component of the global climate, particularly in regard to the water cycle. Glaciers and snowpacks are an important storage mechanism for fresh water; over time, they may sublimate or melt. Snowmelt

776-432: A hailstone becomes too heavy to be supported by the storm's updraft, it falls from the cloud. Hail forms in strong thunderstorm clouds, particularly those with intense updrafts, high liquid water content, great vertical extent, large water droplets, and where a good portion of the cloud layer is below freezing 0 °C (32 °F). Hail-producing clouds are often identifiable by their green coloration. The growth rate

873-581: A key role in Earth's water cycle and climate . In the recent decades, ice volume on Earth has been decreasing due to climate change . The largest declines have occurred in the Arctic and in the mountains located outside of the polar regions. The loss of grounded ice (as opposed to floating sea ice ) is the primary contributor to sea level rise . Humans have been using ice for various purposes for thousands of years. Some historic structures designed to hold ice to provide cooling are over 2,000 years old. Before

970-419: A layer of ice that would form slowly and so avoid a sudden temperature shock to the plant, and not be so thick as to cause damage with its weight. Ablation of ice refers to both its melting and its dissolution . The melting of ice entails the breaking of hydrogen bonds between the water molecules. The ordering of the molecules in the solid breaks down to a less ordered state and the solid melts to become

1067-495: A lesser degree, etc.; thus a "co-valent bond", in essence, means that the atoms share " valence ", such as is discussed in valence bond theory . In the molecule H 2 , the hydrogen atoms share the two electrons via covalent bonding. Covalency is greatest between atoms of similar electronegativities . Thus, covalent bonding does not necessarily require that the two atoms be of the same elements, only that they be of comparable electronegativity. Covalent bonding that entails

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1164-456: A liquid. This is achieved by increasing the internal energy of the ice beyond the melting point . When ice melts it absorbs as much energy as would be required to heat an equivalent amount of water by 80 °C. While melting, the temperature of the ice surface remains constant at 0 °C. The rate of the melting process depends on the efficiency of the energy exchange process. An ice surface in fresh water melts solely by free convection with

1261-436: A low speed. Ice forms on calm water from the shores, a thin layer spreading across the surface, and then downward. Ice on lakes is generally four types: primary, secondary, superimposed and agglomerate. Primary ice forms first. Secondary ice forms below the primary ice in a direction parallel to the direction of the heat flow. Superimposed ice forms on top of the ice surface from rain or water which seeps up through cracks in

1358-458: A mixture of atoms and ions. On the other hand, simple molecular orbital theory correctly predicts Hückel's rule of aromaticity, while simple valence bond theory incorrectly predicts that cyclobutadiene has larger resonance energy than benzene. Although the wavefunctions generated by both theories at the qualitative level do not agree and do not match the stabilization energy by experiment, they can be corrected by configuration interaction . This

1455-581: A naturally occurring crystalline inorganic solid with an ordered structure, ice is considered to be a mineral . Depending on the presence of impurities such as particles of soil or bubbles of air , it can appear transparent or a more or less opaque bluish-white color. Virtually all of the ice on Earth is of a hexagonal crystalline structure denoted as ice I h (spoken as "ice one h"). Depending on temperature and pressure, at least nineteen phases ( packing geometries ) can exist. The most common phase transition to ice I h occurs when liquid water

1552-505: A rate that depends linearly on the water temperature, T ∞ , when T ∞ is less than 3.98 °C, and superlinearly when T ∞ is equal to or greater than 3.98 °C, with the rate being proportional to (T ∞  − 3.98 °C) , with α  =  ⁠ 5 / 3 ⁠ for T ∞ much greater than 8 °C, and α =  ⁠ 4 / 3 ⁠ for in between temperatures T ∞ . In salty ambient conditions, dissolution rather than melting often causes

1649-508: A regular hexagon exhibiting a greater stabilization than the hypothetical 1,3,5-cyclohexatriene. In the case of heterocyclic aromatics and substituted benzenes , the electronegativity differences between different parts of the ring may dominate the chemical behavior of aromatic ring bonds, which otherwise are equivalent. Certain molecules such as xenon difluoride and sulfur hexafluoride have higher co-ordination numbers than would be possible due to strictly covalent bonding according to

1746-420: A single Lewis structure is insufficient to explain the electron configuration in a molecule and its resulting experimentally-determined properties, hence a superposition of structures is needed. The same two atoms in such molecules can be bonded differently in different Lewis structures (a single bond in one, a double bond in another, or even none at all), resulting in a non-integer bond order . The nitrate ion

1843-487: A single oxygen atom covalently bonded to two hydrogen atoms , or H–O–H. However, many of the physical properties of water and ice are controlled by the formation of hydrogen bonds between adjacent oxygen and hydrogen atoms; while it is a weak bond, it is nonetheless critical in controlling the structure of both water and ice. An unusual property of water is that its solid form—ice frozen at atmospheric pressure —is approximately 8.3% less dense than its liquid form; this

1940-746: A soft ball-like shape is formed. So-called " diamond dust ", (METAR code IC ) also known as ice needles or ice crystals, forms at temperatures approaching −40 °C (−40 °F) due to air with slightly higher moisture from aloft mixing with colder, surface-based air. As water drips and re-freezes, it can form hanging icicles , or stalagmite -like structures on the ground. On sloped roofs, buildup of ice can produce an ice dam , which stops melt water from draining properly and potentially leads to damaging leaks. More generally, water vapor depositing onto surfaces due to high relative humidity and then freezing results in various forms of atmospheric icing , or frost . Inside buildings, this can be seen as ice on

2037-471: A temperature of −78.5 °C (−109.3 °F), the vaporization point of solid carbon dioxide (dry ice). Most liquids under increased pressure freeze at higher temperatures because the pressure helps to hold the molecules together. However, the strong hydrogen bonds in water make it different: for some pressures higher than 1 atm (0.10 MPa), water freezes at a temperature below 0 °C (32 °F). Ice, water, and water vapour can coexist at

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2134-574: A thin surface layer, which makes it particularly hazardous to walk across it. Another dangerous form of rotten ice to traverse on foot is candle ice, which develops in columns perpendicular to the surface of a lake. Because it lacks a firm horizontal structure, a person who has fallen through has nothing to hold onto to pull themselves out. Snow crystals form when tiny supercooled cloud droplets (about 10  μm in diameter) freeze . These droplets are able to remain liquid at temperatures lower than −18 °C (255 K; 0 °F), because to freeze,

2231-442: Is a basic cause of freeze-thaw weathering of rock in nature and damage to building foundations and roadways from frost heaving . It is also a common cause of the flooding of houses when water pipes burst due to the pressure of expanding water when it freezes. Because ice is less dense than liquid water, it floats, and this prevents bottom-up freezing of the bodies of water. Instead, a sheltered environment for animal and plant life

2328-427: Is abundant on the Earth's surface, particularly in the polar regions and above the snow line , where it can aggregate from snow to form glaciers and ice sheets . As snowflakes and hail , ice is a common form of precipitation , and it may also be deposited directly by water vapor as frost . The transition from ice to water is melting and from ice directly to water vapor is sublimation . These processes plays

2425-424: Is an important source of seasonal fresh water. The World Meteorological Organization defines several kinds of ice depending on origin, size, shape, influence and so on. Clathrate hydrates are forms of ice that contain gas molecules trapped within its crystal lattice. Ice that is found at sea may be in the form of drift ice floating in the water, fast ice fixed to a shoreline or anchor ice if attached to

2522-498: Is cooled below 0  °C ( 273.15  K , 32  °F ) at standard atmospheric pressure . When water is cooled rapidly ( quenching ), up to three types of amorphous ice can form. Interstellar ice is overwhelmingly low-density amorphous ice (LDA), which likely makes LDA ice the most abundant type in the universe. When cooled slowly, correlated proton tunneling occurs below −253.15  °C ( 20  K , −423.67  °F ) giving rise to macroscopic quantum phenomena . Ice

2619-423: Is defined as where g | n , l , m l , m s ⟩ A ( E ) {\displaystyle g_{|n,l,m_{l},m_{s}\rangle }^{\mathrm {A} }(E)} is the contribution of the atomic orbital | n , l , m l , m s ⟩ {\displaystyle |n,l,m_{l},m_{s}\rangle } of

2716-493: Is denoted as the covalency of the A−B bond, which is specified in the same units of the energy ⁠ E {\displaystyle E} ⁠ . An analogous effect to covalent binding is believed to occur in some nuclear systems, with the difference that the shared fermions are quarks rather than electrons. High energy proton -proton scattering cross-section indicates that quark interchange of either u or d quarks

2813-494: Is divided into four categories: pore ice, vein ice (also known as ice wedges), buried surface ice and intrasedimental ice (from the freezing of underground waters). One example of ice formation in permafrost areas is aufeis - layered ice that forms in Arctic and subarctic stream valleys. Ice, frozen in the stream bed, blocks normal groundwater discharge, and causes the local water table to rise, resulting in water discharge on top of

2910-468: Is done by combining the valence bond covalent function with the functions describing all possible ionic structures or by combining the molecular orbital ground state function with the functions describing all possible excited states using unoccupied orbitals. It can then be seen that the simple molecular orbital approach overestimates the weight of the ionic structures while the simple valence bond approach neglects them. This can also be described as saying that

3007-435: Is equivalent to a volumetric expansion of 9%. The density of ice is 0.9167 –0.9168  g/cm at 0 °C and standard atmospheric pressure (101,325 Pa), whereas water has a density of 0.9998 –0.999863  g/cm at the same temperature and pressure. Liquid water is densest, essentially 1.00 g/cm , at 4 °C and begins to lose its density as the water molecules begin to form the hexagonal crystals of ice as

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3104-484: Is extremely rare otherwise. Even icy moons like Ganymede are expected to mainly consist of other crystalline forms of ice. Water in the interstellar medium is dominated by amorphous ice, making it likely the most common form of water in the universe. Low-density ASW (LDA), also known as hyperquenched glassy water, may be responsible for noctilucent clouds on Earth and is usually formed by deposition of water vapor in cold or vacuum conditions. High-density ASW (HDA)

3201-484: Is formed beneath the floating ice, which protects the underside from short-term weather extremes such as wind chill . Sufficiently thin floating ice allows light to pass through, supporting the photosynthesis of bacterial and algal colonies. When sea water freezes, the ice is riddled with brine-filled channels which sustain sympagic organisms such as bacteria, algae, copepods and annelids . In turn, they provide food for animals such as krill and specialized fish like

3298-452: Is formed by compression of ordinary ice I h or LDA at GPa pressures. Very-high-density ASW (VHDA) is HDA slightly warmed to 160 K under 1–2 GPa pressures. Ice from a theorized superionic water may possess two crystalline structures. At pressures in excess of 500,000 bars (7,300,000 psi) such superionic ice would take on a body-centered cubic structure. However, at pressures in excess of 1,000,000 bars (15,000,000 psi)

3395-448: Is maximized at about −13 °C (9 °F), and becomes vanishingly small much below −30 °C (−22 °F) as supercooled water droplets become rare. For this reason, hail is most common within continental interiors of the mid-latitudes, as hail formation is considerably more likely when the freezing level is below the altitude of 11,000 feet (3,400 m). Entrainment of dry air into strong thunderstorms over continents can increase

3492-408: Is one such example with three equivalent structures. The bond between the nitrogen and each oxygen is a double bond in one structure and a single bond in the other two, so that the average bond order for each N–O interaction is ⁠ 2 + 1 + 1 / 3 ⁠ = ⁠ 4 / 3 ⁠ . [REDACTED] In organic chemistry , when a molecule with a planar ring obeys Hückel's rule , where

3589-464: Is over 70% ice on its surface is said to be covered by pack ice. Fully formed sea ice can be forced together by currents and winds to form pressure ridges up to 12 metres (39 ft) tall. On the other hand, active wave activity can reduce sea ice to small, regularly shaped pieces, known as pancake ice . Sometimes, wind and wave activity "polishes" sea ice to perfectly spherical pieces known as ice eggs . The largest ice formations on Earth are

3686-409: Is shifted toward slightly lower energies. Thus, ice appears blue, with a slightly greener tint than liquid water. Since absorption is cumulative, the color effect intensifies with increasing thickness or if internal reflections cause the light to take a longer path through the ice. Other colors can appear in the presence of light absorbing impurities, where the impurity is dictating the color rather than

3783-531: Is therefore slower than melting. Ice has long been valued as a means of cooling. In 400 BC Iran, Persian engineers had already developed techniques for ice storage in the desert through the summer months. During the winter, ice was transported from harvesting pools and nearby mountains in large quantities to be stored in specially designed, naturally cooled refrigerators , called yakhchal (meaning ice storage ). Yakhchals were large underground spaces (up to 5000 m ) that had thick walls (at least two meters at

3880-446: The bald notothen , fed upon in turn by larger animals such as emperor penguins and minke whales . When ice melts, it absorbs as much energy as it would take to heat an equivalent mass of water by 80 °C (176 °F). During the melting process, the temperature remains constant at 0 °C (32 °F). While melting, any energy added breaks the hydrogen bonds between ice (water) molecules. Energy becomes available to increase

3977-615: The octet rule . This is explained by the three-center four-electron bond ("3c–4e") model which interprets the molecular wavefunction in terms of non-bonding highest occupied molecular orbitals in molecular orbital theory and resonance of sigma bonds in valence bond theory . In three-center two-electron bonds ("3c–2e") three atoms share two electrons in bonding. This type of bonding occurs in boron hydrides such as diborane (B 2 H 6 ), which are often described as electron deficient because there are not enough valence electrons to form localized (2-centre 2-electron) bonds joining all

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4074-755: The triple point , which is exactly 273.16 K (0.01 °C) at a pressure of 611.657  Pa . The kelvin was defined as ⁠ 1 / 273.16 ⁠ of the difference between this triple point and absolute zero , though this definition changed in May 2019. Unlike most other solids, ice is difficult to superheat . In an experiment, ice at −3 °C was superheated to about 17 °C for about 250 picoseconds . Subjected to higher pressures and varying temperatures, ice can form in nineteen separate known crystalline phases at various densities, along with hypothetical proposed phases of ice that have not been observed. With care, at least fifteen of these phases (one of

4171-473: The "Ice King", worked on developing better insulation products for long distance shipments of ice, especially to the tropics; this became known as the ice trade. Between 1812 and 1822, under Lloyd Hesketh Bamford Hesketh 's instruction, Gwrych Castle was built with 18 large towers, one of those towers is called the 'Ice Tower'. Its sole purpose was to store Ice. Trieste sent ice to Egypt , Corfu , and Zante ; Switzerland, to France; and Germany sometimes

4268-948: The United States, with a combined value of shipments of $ 595,487,000. Home refrigerators can also make ice with a built in icemaker , which will typically make ice cubes or crushed ice. The first such device was presented in 1965 by Frigidaire . Ice forming on roads is a common winter hazard, and black ice particularly dangerous because it is very difficult to see. It is both very transparent, and often forms specifically in shaded (and therefore cooler and darker) areas, i.e. beneath overpasses . Covalently Covalent bonding also includes many kinds of interactions, including σ-bonding , π-bonding , metal-to-metal bonding , agostic interactions , bent bonds , three-center two-electron bonds and three-center four-electron bonds . The term covalent bond dates from 1939. The prefix co- means jointly, associated in action, partnered to

4365-459: The ability to form three or four electron pair bonds, often form such large macromolecular structures. Bonds with one or three electrons can be found in radical species, which have an odd number of electrons. The simplest example of a 1-electron bond is found in the dihydrogen cation , H 2 . One-electron bonds often have about half the bond energy of a 2-electron bond, and are therefore called "half bonds". However, there are exceptions: in

4462-475: The ablation of ice. For example, the temperature of the Arctic Ocean is generally below the melting point of ablating sea ice. The phase transition from solid to liquid is achieved by mixing salt and water molecules, similar to the dissolution of sugar in water, even though the water temperature is far below the melting point of the sugar. However, the dissolution rate is limited by salt concentration and

4559-432: The atom A to the total electronic density of states ⁠ g ( E ) {\displaystyle g(E)} ⁠ of the solid where the outer sum runs over all atoms A of the unit cell. The energy window ⁠ [ E 0 , E 1 ] {\displaystyle [E_{0},E_{1}]} ⁠ is chosen in such a way that it encompasses all of the relevant bands participating in

4656-986: The atoms together, but generally, there are negligible forces of attraction between molecules. Such covalent substances are usually gases, for example, HCl , SO 2 , CO 2 , and CH 4 . In molecular structures, there are weak forces of attraction. Such covalent substances are low-boiling-temperature liquids (such as ethanol ), and low-melting-temperature solids (such as iodine and solid CO 2 ). Macromolecular structures have large numbers of atoms linked by covalent bonds in chains, including synthetic polymers such as polyethylene and nylon , and biopolymers such as proteins and starch . Network covalent structures (or giant covalent structures) contain large numbers of atoms linked in sheets (such as graphite ), or 3-dimensional structures (such as diamond and quartz ). These substances have high melting and boiling points, are frequently brittle, and tend to have high electrical resistivity . Elements that have high electronegativity , and

4753-400: The atoms. However the more modern description using 3c–2e bonds does provide enough bonding orbitals to connect all the atoms, so that the molecules can instead be classified as electron-precise. Each such bond (2 per molecule in diborane) contains a pair of electrons which connect the boron atoms to each other in a banana shape, with a proton (the nucleus of a hydrogen atom) in the middle of

4850-419: The base) made of a specific type of mortar called sarooj made from sand, clay, egg whites, lime, goat hair, and ash. The mortar was resistant to heat transfer, helping to keep the ice cool enough not to melt; it was also impenetrable by water. Yakhchals often included a qanat and a system of windcatchers that could lower internal temperatures to frigid levels, even during the heat of the summer. One use for

4947-737: The bond covalency can be provided in this way. The mass center ⁠ c m ( n , l , m l , m s ) {\displaystyle cm(n,l,m_{l},m_{s})} ⁠ of an atomic orbital | n , l , m l , m s ⟩ , {\displaystyle |n,l,m_{l},m_{s}\rangle ,} with quantum numbers ⁠ n , {\displaystyle n,} ⁠ ⁠ l , {\displaystyle l,} ⁠ ⁠ m l , {\displaystyle m_{l},} ⁠ ⁠ m s , {\displaystyle m_{s},} ⁠ for atom A

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5044-430: The bond, sharing electrons with both boron atoms. In certain cluster compounds , so-called four-center two-electron bonds also have been postulated. After the development of quantum mechanics, two basic theories were proposed to provide a quantum description of chemical bonding: valence bond (VB) theory and molecular orbital (MO) theory . A more recent quantum description is given in terms of atomic contributions to

5141-438: The bond. If the range to select is unclear, it can be identified in practice by examining the molecular orbitals that describe the electron density along with the considered bond. The relative position ⁠ C n A l A , n B l B {\displaystyle C_{n_{\mathrm {A} }l_{\mathrm {A} },n_{\mathrm {B} }l_{\mathrm {B} }}} ⁠ of

5238-440: The case of dilithium , the bond is actually stronger for the 1-electron Li 2 than for the 2-electron Li 2 . This exception can be explained in terms of hybridization and inner-shell effects. The simplest example of three-electron bonding can be found in the helium dimer cation, He 2 . It is considered a "half bond" because it consists of only one shared electron (rather than two); in molecular orbital terms,

5335-587: The connected atoms which determines the chemical polarity of the bond. Two atoms with equal electronegativity will make nonpolar covalent bonds such as H–H. An unequal relationship creates a polar covalent bond such as with H−Cl. However polarity also requires geometric asymmetry , or else dipoles may cancel out, resulting in a non-polar molecule. There are several types of structures for covalent substances, including individual molecules, molecular structures , macromolecular structures and giant covalent structures. Individual molecules have strong bonds that hold

5432-605: The contributions of the magnetic and spin quantum numbers are summed. According to this definition, the relative position of the A levels with respect to the B levels is where, for simplicity, we may omit the dependence from the principal quantum number ⁠ n {\displaystyle n} ⁠ in the notation referring to ⁠ C n A l A , n B l B . {\displaystyle C_{n_{\mathrm {A} }l_{\mathrm {A} },n_{\mathrm {B} }l_{\mathrm {B} }}.} ⁠ In this formalism,

5529-427: The droplet to act as a nucleus. Our understanding of what particles make efficient ice nuclei is poor – what we do know is they are very rare compared to that cloud condensation nuclei on which liquid droplets form. Clays, desert dust and biological particles may be effective, although to what extent is unclear. Artificial nuclei are used in cloud seeding . The droplet then grows by condensation of water vapor onto

5626-422: The electronic density of states. The two theories represent two ways to build up the electron configuration of the molecule. For valence bond theory, the atomic hybrid orbitals are filled with electrons first to produce a fully bonded valence configuration, followed by performing a linear combination of contributing structures ( resonance ) if there are several of them. In contrast, for molecular orbital theory

5723-412: The feasibility and speed of computer calculations compared to nonorthogonal valence bond orbitals. Evaluation of bond covalency is dependent on the basis set for approximate quantum-chemical methods such as COOP (crystal orbital overlap population), COHP (Crystal orbital Hamilton population), and BCOOP (Balanced crystal orbital overlap population). To overcome this issue, an alternative formulation of

5820-449: The freezing point is reached. This is due to hydrogen bonding dominating the intermolecular forces, which results in a packing of molecules less compact in the solid. The density of ice increases slightly with decreasing temperature and has a value of 0.9340 g/cm at −180 °C (93 K). When water freezes, it increases in volume (about 9% for fresh water). The effect of expansion during freezing can be dramatic, and ice expansion

5917-465: The frequency of hail by promoting evaporative cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in. Accordingly, hail is actually less common in the tropics despite a much higher frequency of thunderstorms than in the mid-latitudes because the atmosphere over the tropics tends to be warmer over a much greater depth. Hail in the tropics occurs mainly at higher elevations. Ice pellets ( METAR code PL ) are

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6014-534: The frozen layer. This water then freezes, causing the water table to rise further and repeat the cycle. The result is a stratified ice deposit, often several meters thick. Snow line and snow fields are two related concepts, in that snow fields accumulate on top of and ablate away to the equilibrium point (the snow line) in an ice deposit. Ice which forms on moving water tends to be less uniform and stable than ice which forms on calm water. Ice jams (sometimes called "ice dams"), when broken chunks of ice pile up, are

6111-400: The greater the value of ⁠ C A , B , {\displaystyle C_{\mathrm {A,B} },} ⁠ the higher the overlap of the selected atomic bands, and thus the electron density described by those orbitals gives a more covalent A−B bond. The quantity ⁠ C A , B {\displaystyle C_{\mathrm {A,B} }} ⁠

6208-636: The greatest ice hazard on rivers. Ice jams can cause flooding, damage structures in or near the river, and damage vessels on the river. Ice jams can cause some hydropower industrial facilities to completely shut down. An ice dam is a blockage from the movement of a glacier which may produce a proglacial lake . Heavy ice flows in rivers can also damage vessels and require the use of an icebreaker vessel to keep navigation possible. Ice discs are circular formations of ice floating on river water. They form within eddy currents , and their position results in asymmetric melting, which makes them continuously rotate at

6305-503: The hailstones to the upper part of the cloud. The updraft dissipates and the hailstones fall down, back into the updraft, and are lifted up again. Hail has a diameter of 5 millimetres (0.20 in) or more. Within METAR code, GR is used to indicate larger hail, of a diameter of at least 6.4 millimetres (0.25 in) and GS for smaller. Stones of 19 millimetres (0.75 in), 25 millimetres (1.0 in) and 44 millimetres (1.75 in) are

6402-464: The ice exerted by any object. However, the significance of this hypothesis is disputed by experiments showing a high coefficient of friction for ice using atomic force microscopy . Thus, the mechanism controlling the frictional properties of ice is still an active area of scientific study. A comprehensive theory of ice friction must take into account all of the aforementioned mechanisms to estimate friction coefficient of ice against various materials as

6499-429: The ice itself. For instance, icebergs containing impurities (e.g., sediments, algae, air bubbles) can appear brown, grey or green. Because ice in natural environments is usually close to its melting temperature, its hardness shows pronounced temperature variations. At its melting point, ice has a Mohs hardness of 2 or less, but the hardness increases to about 4 at a temperature of −44 °C (−47 °F) and to 6 at

6596-456: The ice layer is caused by friction. However, this theory does not sufficiently explain why ice is slippery when standing still even at below-zero temperatures. Subsequent research suggested that ice molecules at the interface cannot properly bond with the molecules of the mass of ice beneath (and thus are free to move like molecules of liquid water). These molecules remain in a semi-liquid state, providing lubrication regardless of pressure against

6693-471: The ice surfaces. Ice storm is a type of winter storm characterized by freezing rain , which produces a glaze of ice on surfaces, including roads and power lines . In the United States, a quarter of winter weather events produce glaze ice, and utilities need to be prepared to minimize damages. Hail forms in storm clouds when supercooled water droplets freeze on contact with condensation nuclei , such as dust or dirt . The storm's updraft blows

6790-481: The ice was to create chilled treats for royalty. There were thriving industries in 16th–17th century England whereby low-lying areas along the Thames Estuary were flooded during the winter, and ice harvested in carts and stored inter-seasonally in insulated wooden houses as a provision to an icehouse often located in large country houses, and widely used to keep fish fresh when caught in distant waters. This

6887-416: The ice which often settles when loaded with snow. An ice shove occurs when ice movement, caused by ice expansion and/or wind action, occurs to the extent that ice pushes onto the shores of lakes, often displacing sediment that makes up the shoreline. Shelf ice is formed when floating pieces of ice are driven by the wind piling up on the windward shore. This kind of ice may contain large air pockets under

6984-603: The ice, would melt a thin layer, providing sufficient lubrication for the blade to glide across the ice. Yet, 1939 research by Frank P. Bowden and T. P. Hughes found that skaters would experience a lot more friction than they actually do if it were the only explanation. Further, the optimum temperature for figure skating is −5.5 °C (22 °F; 268 K) and −9 °C (16 °F; 264 K) for hockey; yet, according to pressure melting theory, skating below −4 °C (25 °F; 269 K) would be outright impossible. Instead, Bowden and Hughes argued that heating and melting of

7081-427: The invention of refrigeration technology, the only way to safely store food without modifying it through preservatives was to use ice. Sufficiently solid surface ice makes waterways accessible to land transport during winter, and dedicated ice roads may be maintained. Ice also plays a major role in winter sports . Ice possesses a regular crystalline structure based on the molecule of water, which consists of

7178-515: The known exceptions being ice X) can be recovered at ambient pressure and low temperature in metastable form. The types are differentiated by their crystalline structure, proton ordering, and density. There are also two metastable phases of ice under pressure, both fully hydrogen-disordered; these are Ice IV and Ice XII. Ice XII was discovered in 1996. In 2006, Ice XIII and Ice XIV were discovered. Ices XI, XIII, and XIV are hydrogen-ordered forms of ices I h , V, and XII respectively. In 2009, ice XV

7275-495: The large number of glaciers it contains. They cover an area of around 80,000 km (31,000 sq mi), and have a combined volume of between 3,000-4,700 km . These glaciers are nicknamed "Asian water towers", because their meltwater run-off feeds into rivers which provide water for an estimated two billion people. Permafrost refers to soil or underwater sediment which continuously remains below 0 °C (32 °F) for two years or more. The ice within permafrost

7372-413: The mass center of | n A , l A ⟩ {\displaystyle |n_{\mathrm {A} },l_{\mathrm {A} }\rangle } levels of atom A with respect to the mass center of | n B , l B ⟩ {\displaystyle |n_{\mathrm {B} },l_{\mathrm {B} }\rangle } levels of atom B is given as where

7469-524: The most frequently reported hail sizes in North America. Hailstones can grow to 15 centimetres (6 in) and weigh more than 0.5 kilograms (1.1 lb). In large hailstones, latent heat released by further freezing may melt the outer shell of the hailstone. The hailstone then may undergo 'wet growth', where the liquid outer shell collects other smaller hailstones. The hailstone gains an ice layer and grows increasingly larger with each ascent. Once

7566-458: The number of π electrons fit the formula 4 n  + 2 (where n is an integer), it attains extra stability and symmetry. In benzene , the prototypical aromatic compound, there are 6 π bonding electrons ( n  = 1, 4 n  + 2 = 6). These occupy three delocalized π molecular orbitals ( molecular orbital theory ) or form conjugate π bonds in two resonance structures that linearly combine ( valence bond theory ), creating

7663-514: The process to an even older author, Ibn Bakhtawayhi, of whom nothing is known. Ice is now produced on an industrial scale, for uses including food storage and processing, chemical manufacturing, concrete mixing and curing, and consumer or packaged ice. Most commercial icemakers produce three basic types of fragmentary ice: flake, tubular and plate, using a variety of techniques. Large batch ice makers can produce up to 75 tons of ice per day. In 2002, there were 426 commercial ice-making companies in

7760-427: The quantum theory of the atom; the outer shell of a carbon atom is the n  = 2 shell, which can hold eight electrons, whereas the outer (and only) shell of a hydrogen atom is the n  = 1 shell, which can hold only two. While the idea of shared electron pairs provides an effective qualitative picture of covalent bonding, quantum mechanics is needed to understand the nature of these bonds and predict

7857-425: The seafloor. Ice which calves (breaks off) from an ice shelf or a coastal glacier may become an iceberg. The aftermath of calving events produces a loose mixture of snow and ice known as Ice mélange . Sea ice forms in several stages. At first, small, millimeter-scale crystals accumulate on the water surface in what is known as frazil ice . As they become somewhat larger and more consistent in shape and cover,

7954-712: The sharing of electron pairs between atoms (and in 1926 he also coined the term " photon " for the smallest unit of radiant energy). He introduced the Lewis notation or electron dot notation or Lewis dot structure , in which valence electrons (those in the outer shell) are represented as dots around the atomic symbols. Pairs of electrons located between atoms represent covalent bonds. Multiple pairs represent multiple bonds, such as double bonds and triple bonds . An alternative form of representation, not shown here, has bond-forming electron pairs represented as solid lines. Lewis proposed that an atom forms enough covalent bonds to form

8051-676: The sharing of electrons over more than two atoms is said to be delocalized . The term covalence in regard to bonding was first used in 1919 by Irving Langmuir in a Journal of the American Chemical Society article entitled "The Arrangement of Electrons in Atoms and Molecules". Langmuir wrote that "we shall denote by the term covalence the number of pairs of electrons that a given atom shares with its neighbors." The idea of covalent bonding can be traced several years before 1919 to Gilbert N. Lewis , who in 1916 described

8148-533: The simple molecular orbital approach neglects electron correlation while the simple valence bond approach overestimates it. Modern calculations in quantum chemistry usually start from (but ultimately go far beyond) a molecular orbital rather than a valence bond approach, not because of any intrinsic superiority in the former but rather because the MO approach is more readily adapted to numerical computations. Molecular orbitals are orthogonal, which significantly increases

8245-406: The strongest covalent bonds and are due to head-on overlapping of orbitals on two different atoms. A single bond is usually a σ bond. Pi (π) bonds are weaker and are due to lateral overlap between p (or d) orbitals. A double bond between two given atoms consists of one σ and one π bond, and a triple bond is one σ and two π bonds. Covalent bonds are also affected by the electronegativity of

8342-440: The structure may shift to a more stable face-centered cubic lattice. It is speculated that superionic ice could compose the interior of ice giants such as Uranus and Neptune. Ice is " slippery " because it has a low coefficient of friction. This subject was first scientifically investigated in the 19th century. The preferred explanation at the time was " pressure melting " -i.e. the blade of an ice skate, upon exerting pressure on

8439-531: The structures and properties of simple molecules. Walter Heitler and Fritz London are credited with the first successful quantum mechanical explanation of a chemical bond ( molecular hydrogen ) in 1927. Their work was based on the valence bond model, which assumes that a chemical bond is formed when there is good overlap between the atomic orbitals of participating atoms. Atomic orbitals (except for s orbitals) have specific directional properties leading to different types of covalent bonds. Sigma (σ) bonds are

8536-705: The summer. The advent of artificial refrigeration technology made the delivery of ice obsolete. Ice is still harvested for ice and snow sculpture events . For example, a swing saw is used to get ice for the Harbin International Ice and Snow Sculpture Festival each year from the frozen surface of the Songhua River . The earliest known written process to artificially make ice is by the 13th-century writings of Arab historian Ibn Abu Usaybia in his book Kitab Uyun al-anba fi tabaqat-al-atibba concerning medicine in which Ibn Abu Usaybia attributes

8633-443: The surface of un-insulated windows. Hoar frost is common in the environment, particularly in the low-lying areas such as valleys . In Antarctica, the temperatures can be so low that electrostatic attraction is increased to the point hoarfrost on snow sticks together when blown by wind into tumbleweed -like balls known as yukimarimo . Sometimes, drops of water crystallize on cold objects as rime instead of glaze. Soft rime has

8730-441: The thermal energy (temperature) only after enough hydrogen bonds are broken that the ice can be considered liquid water. The amount of energy consumed in breaking hydrogen bonds in the transition from ice to water is known as the heat of fusion . As with water, ice absorbs light at the red end of the spectrum preferentially as the result of an overtone of an oxygen–hydrogen (O–H) bond stretch. Compared with water, this absorption

8827-715: The third electron is in an anti-bonding orbital which cancels out half of the bond formed by the other two electrons. Another example of a molecule containing a 3-electron bond, in addition to two 2-electron bonds, is nitric oxide , NO. The oxygen molecule, O 2 can also be regarded as having two 3-electron bonds and one 2-electron bond, which accounts for its paramagnetism and its formal bond order of 2. Chlorine dioxide and its heavier analogues bromine dioxide and iodine dioxide also contain three-electron bonds. Molecules with odd-electron bonds are usually highly reactive. These types of bond are only stable between atoms with similar electronegativities. There are situations whereby

8924-486: The two ice sheets which almost completely cover the world's largest island, Greenland , and the continent of Antarctica . These ice sheets have an average thickness of over 1 km (0.6 mi) and have existed for millions of years. Other major ice formations on land include ice caps , ice fields , ice streams and glaciers . In particular, the Hindu Kush region is known as the Earth's "Third Pole" due to

9021-552: The understanding of reaction mechanisms . As molecular orbital theory builds the molecular wavefunction out of delocalized orbitals, it is more suited for the calculation of ionization energies and the understanding of spectral absorption bands . At the qualitative level, both theories contain incorrect predictions. Simple (Heitler–London) valence bond theory correctly predicts the dissociation of homonuclear diatomic molecules into separate atoms, while simple (Hartree–Fock) molecular orbital theory incorrectly predicts dissociation into

9118-433: The water surface begins to look "oily" from above, so this stage is called grease ice . Then, ice continues to clump together, and solidify into flat cohesive pieces known as ice floes . Ice floes are the basic building blocks of sea ice cover, and their horizontal size (defined as half of their diameter ) varies dramatically, with the smallest measured in centimeters and the largest in hundreds of kilometers. An area which

9215-456: Was allegedly copied by an Englishman who had seen the same activity in China. Ice was imported into England from Norway on a considerable scale as early as 1823. In the United States, the first cargo of ice was sent from New York City to Charleston, South Carolina , in 1799, and by the first half of the 19th century, ice harvesting had become a big business. Frederic Tudor , who became known as

9312-411: Was found at extremely high pressures and −143 °C. At even higher pressures, ice is predicted to become a metal ; this has been variously estimated to occur at 1.55 TPa or 5.62 TPa. As well as crystalline forms, solid water can exist in amorphous states as amorphous solid water (ASW) of varying densities. In outer space, hexagonal crystalline ice is present in the ice volcanoes , but

9409-509: Was supplied from Bavarian lakes. From 1930s and up until 1994, the Hungarian Parliament building used ice harvested in the winter from Lake Balaton for air conditioning. Ice houses were used to store ice formed in the winter, to make ice available all year long, and an early type of refrigerator known as an icebox was cooled using a block of ice placed inside it. Many cities had a regular ice delivery service during

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