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99-417: Due to the significant amount of organic matter in the tank (approx. 11.5% of the dry weight of sediment), it emits approx. 400 mg of methane per area of 1 m (which is approx. 27% of the total amount of gases emitted from the sediment of average 3114 ml m d). For this reason, is considered an important source of greenhouse gases emission . The tank has three basic functions: Wloclawek reservoir tank

198-570: A coal deposit, while enhanced coal bed methane recovery is a method of recovering methane from non-mineable coal seams). It is associated with other hydrocarbon fuels, and sometimes accompanied by helium and nitrogen . Methane is produced at shallow levels (low pressure) by anaerobic decay of organic matter and reworked methane from deep under the Earth's surface. In general, the sediments that generate natural gas are buried deeper and at higher temperatures than those that contain oil . Methane

297-458: A hydrogen halide molecule and a methyl radical ( •CH 3 ). The methyl radical then reacts with a molecule of the halogen to form a molecule of the halomethane, with a new halogen atom as byproduct. Similar reactions can occur on the halogenated product, leading to replacement of additional hydrogen atoms by halogen atoms with dihalomethane , trihalomethane , and ultimately, tetrahalomethane structures, depending upon reaction conditions and

396-519: A stub . You can help Misplaced Pages by expanding it . Methane Methane ( US : / ˈ m ɛ θ eɪ n / METH -ayn , UK : / ˈ m iː θ eɪ n / MEE -thayn ) is a chemical compound with the chemical formula CH 4 (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride , the simplest alkane , and the main constituent of natural gas . The abundance of methane on Earth makes it an economically attractive fuel , although capturing and storing it

495-489: A 10% contribution of the second. Indeed, visible light is already enough to excite electrons in most transition metals, and they often continuously "flow" through different configurations when that happens (copper and its group are an exception). Similar ion-like 3d  4s configurations occur in transition metal complexes as described by the simple crystal field theory , even if the metal has oxidation state  0. For example, chromium hexacarbonyl can be described as

594-399: A bare ion has a configuration of [Rn] 5f , yet in most Th compounds the thorium atom has a 6d configuration instead. Mostly, what is present is rather a superposition of various configurations. For instance, copper metal is poorly described by either an [Ar] 3d  4s or an [Ar] 3d  4s configuration, but is rather well described as a 90% contribution of the first and

693-465: A chromium atom (not ion) surrounded by six carbon monoxide ligands . The electron configuration of the central chromium atom is described as 3d with the six electrons filling the three lower-energy d orbitals between the ligands. The other two d orbitals are at higher energy due to the crystal field of the ligands. This picture is consistent with the experimental fact that the complex is diamagnetic , meaning that it has no unpaired electrons. However, in

792-428: A half-filled or completely filled subshell. The apparent paradox arises when electrons are removed from the transition metal atoms to form ions . The first electrons to be ionized come not from the 3d-orbital, as one would expect if it were "higher in energy", but from the 4s-orbital. This interchange of electrons between 4s and 3d is found for all atoms of the first series of transition metals. The configurations of

891-403: A more accurate description using molecular orbital theory , the d-like orbitals occupied by the six electrons are no longer identical with the d orbitals of the free atom. There are several more exceptions to Madelung's rule among the heavier elements, and as atomic number increases it becomes more and more difficult to find simple explanations such as the stability of half-filled subshells. It

990-416: A more stable +2 oxidation state corresponding to losing only the 6s electrons. Contrariwise, uranium as [Rn] 5f 6d 7s is not very stable in the +3 oxidation state either, preferring +4 and +6. The electron-shell configuration of elements beyond hassium has not yet been empirically verified, but they are expected to follow Madelung's rule without exceptions until element 120 . Element 121 should have

1089-422: A present-day chemist: sulfur was given as 2.4.4.6 instead of 1s  2s  2p  3s  3p (2.8.6). Bohr used 4 and 6 following Alfred Werner 's 1893 paper. In fact, the chemists accepted the concept of atoms long before the physicists. Langmuir began his paper referenced above by saying, «…The problem of the structure of atoms has been attacked mainly by physicists who have given little consideration to

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1188-487: A pressure of one atmosphere . As a gas, it is flammable over a range of concentrations (5.4%–17%) in air at standard pressure . Solid methane exists in several modifications . Presently nine are known. Cooling methane at normal pressure results in the formation of methane I. This substance crystallizes in the cubic system ( space group Fm 3 m). The positions of the hydrogen atoms are not fixed in methane I, i.e. methane molecules may rotate freely. Therefore, it

1287-400: A requirement for pure methane can easily be fulfilled by steel gas bottle from standard gas suppliers. Methane is the major component of natural gas, about 87% by volume. The major source of methane is extraction from geological deposits known as natural gas fields , with coal seam gas extraction becoming a major source (see coal bed methane extraction , a method for extracting methane from

1386-399: A resource that is otherwise difficult to transport for its weight, ash content, low calorific value and propensity to spontaneous combustion during storage and transport. A number of similar plants exist around the world, although mostly these plants are targeted towards the production of long chain alkanes for use as gasoline , diesel , or feedstock to other processes. Power to methane

1485-498: A set of many-electron solutions that cannot be calculated exactly (although there are mathematical approximations available, such as the Hartree–Fock method ). The fact that the aufbau principle is based on an approximation can be seen from the fact that there is an almost-fixed filling order at all, that, within a given shell, the s-orbital is always filled before the p-orbitals. In a hydrogen-like atom , which only has one electron,

1584-431: A spin of − 1 ⁄ 2 (with a down-arrow). A subshell is the set of states defined by a common azimuthal quantum number , l , within a shell. The value of l is in the range from 0 to n  − 1. The values l  = 0, 1, 2, 3 correspond to the s, p, d, and f labels, respectively. For example, the 3d subshell has n  = 3 and l  = 2. The maximum number of electrons that can be placed in

1683-452: A subshell is given by 2(2 l + 1). This gives two electrons in an s subshell, six electrons in a p subshell, ten electrons in a d subshell and fourteen electrons in an f subshell. The numbers of electrons that can occupy each shell and each subshell arise from the equations of quantum mechanics, in particular the Pauli exclusion principle , which states that no two electrons in

1782-485: A subshell is unoccupied despite higher subshells being occupied (as is the case in some ions, as well as certain neutral atoms shown to deviate from the Madelung rule ), the empty subshell is either denoted with a superscript 0 or left out altogether. For example, neutral palladium may be written as either [Kr] 4d 5s or simply [Kr] 4d , and the lanthanum(III) ion may be written as either [Xe] 4f or simply [Xe]. It

1881-406: Is a halogen : fluorine (F), chlorine (Cl), bromine (Br), or iodine (I). This mechanism for this process is called free radical halogenation . It is initiated when UV light or some other radical initiator (like peroxides ) produces a halogen atom . A two-step chain reaction ensues in which the halogen atom abstracts a hydrogen atom from a methane molecule, resulting in the formation of

1980-796: Is a plastic crystal . The primary chemical reactions of methane are combustion , steam reforming to syngas , and halogenation . In general, methane reactions are difficult to control. Partial oxidation of methane to methanol ( C H 3 O H ), a more convenient, liquid fuel, is challenging because the reaction typically progresses all the way to carbon dioxide and water even with an insufficient supply of oxygen . The enzyme methane monooxygenase produces methanol from methane, but cannot be used for industrial-scale reactions. Some homogeneously catalyzed systems and heterogeneous systems have been developed, but all have significant drawbacks. These generally operate by generating protected products which are shielded from overoxidation. Examples include

2079-448: Is a tetrahedral molecule with four equivalent C–H bonds . Its electronic structure is described by four bonding molecular orbitals (MOs) resulting from the overlap of the valence orbitals on C and H . The lowest-energy MO is the result of the overlap of the 2s orbital on carbon with the in-phase combination of the 1s orbitals on the four hydrogen atoms. Above this energy level is a triply degenerate set of MOs that involve overlap of

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2178-537: Is a technology that uses electrical power to produce hydrogen from water by electrolysis and uses the Sabatier reaction to combine hydrogen with carbon dioxide to produce methane. Methane can be produced by protonation of methyl lithium or a methyl Grignard reagent such as methylmagnesium chloride . It can also be made from anhydrous sodium acetate and dry sodium hydroxide , mixed and heated above 300 °C (with sodium carbonate as byproduct). In practice,

2277-553: Is abiotic. Abiotic means that methane is created from inorganic compounds, without biological activity, either through magmatic processes or via water-rock reactions that occur at low temperatures and pressures, like serpentinization . Most of Earth's methane is biogenic and is produced by methanogenesis , a form of anaerobic respiration only known to be conducted by some members of the domain Archaea . Methanogens occur in landfills and soils , ruminants (for example, cattle ),

2376-399: Is also true for the p-orbitals, which are not explicitly shown because they are only actually occupied for lawrencium in gas-phase ground states.) The various anomalies describe the free atoms and do not necessarily predict chemical behavior. Thus for example neodymium typically forms the +3 oxidation state, despite its configuration [Xe] 4f 5d 6s that if interpreted naïvely would suggest

2475-404: Is difficult because it is a gas at standard temperature and pressure . In the Earth's atmosphere methane is transparent to visible light but absorbs infrared radiation, acting as a greenhouse gas . Methane is an organic compound , and among the simplest of organic compounds. Methane is also a hydrocarbon . Naturally occurring methane is found both below ground and under the seafloor and

2574-414: Is discussion in the contemporary literature on whether this exception should be retained). The electrons in the valence (outermost) shell largely determine each element's chemical properties . The similarities in the chemical properties were remarked on more than a century before the idea of electron configuration. The aufbau principle rests on a fundamental postulate that the order of orbital energies

2673-428: Is easier to store than hydrogen due to its higher boiling point and density, as well as its lack of hydrogen embrittlement . The lower molecular weight of the exhaust also increases the fraction of the heat energy which is in the form of kinetic energy available for propulsion, increasing the specific impulse of the rocket. Compared to liquid hydrogen , the specific energy of methane is lower but this disadvantage

2772-423: Is equivalent to neon is abbreviated as [Ne], allowing the configuration of phosphorus to be written as [Ne] 3s  3p rather than writing out the details of the configuration of neon explicitly. This convention is useful as it is the electrons in the outermost shell that most determine the chemistry of the element. For a given configuration, the order of writing the orbitals is not completely fixed since only

2871-460: Is essentially instantaneous. From approx. 2004. In the event of high water levels acts as a storage reservoir. On 17 May at the dam in Wloclawek thrown water (3,000 m³/s), preparing for the arrival of the flood wave. 22 May inflow was 6,000 m³/s, a snapshot already amounted to 5700 m³/s. During the climax assumed dump 6,300 m³/s. May 23, at 14 the culmination wave reached Wloclawek, but the water level

2970-453: Is fixed, both for a given element and between different elements; in both cases this is only approximately true. It considers atomic orbitals as "boxes" of fixed energy into which can be placed two electrons and no more. However, the energy of an electron "in" an atomic orbital depends on the energies of all the other electrons of the atom (or ion, or molecule, etc.). There are no "one-electron solutions" for systems of more than one electron, only

3069-416: Is formed by both geological and biological processes. The largest reservoir of methane is under the seafloor in the form of methane clathrates . When methane reaches the surface and the atmosphere , it is known as atmospheric methane . The Earth's atmospheric methane concentration has increased by about 160% since 1750, with the overwhelming percentage caused by human activity. It accounted for 20% of

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3168-403: Is generally transported in bulk by pipeline in its natural gas form, or by LNG carriers in its liquefied form; few countries transport it by truck. Electron configuration In atomic physics and quantum chemistry , the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals . For example,

3267-409: Is increasing the amount of methane released from wetlands due to increased temperatures and altered rainfall patterns. This phenomeon is called wetland methane feedback . Rice cultivation generates as much as 12% of total global methane emissions due to the long-term flooding of rice fields. Ruminants, such as cattle, belch methane, accounting for about 22% of the U.S. annual methane emissions to

3366-446: Is lower than that of any other hydrocarbon, but the ratio of the heat of combustion (891 kJ/mol) to the molecular mass (16.0 g/mol, of which 12.0 g/mol is carbon) shows that methane, being the simplest hydrocarbon, produces more heat per mass unit (55.7 kJ/g) than other complex hydrocarbons. In many areas with a dense enough population, methane is piped into homes and businesses for heating , cooking, and industrial uses. In this context it

3465-460: Is mostly composed of methane, is used to produce hydrogen gas on an industrial scale. Steam methane reforming (SMR), or simply known as steam reforming, is the standard industrial method of producing commercial bulk hydrogen gas. More than 50 million metric tons are produced annually worldwide (2013), principally from the SMR of natural gas. Much of this hydrogen is used in petroleum refineries , in

3564-430: Is obtained by promoting a 3s electron to the 3p subshell, to obtain the 1s  2s  2p  3p configuration, abbreviated as the 3p level. Atoms can move from one configuration to another by absorbing or emitting energy. In a sodium-vapor lamp for example, sodium atoms are excited to the 3p level by an electrical discharge, and return to the ground state by emitting yellow light of wavelength 589 nm. Usually,

3663-512: Is obtained by the reaction of CO with water via the water-gas shift reaction : This reaction is mildly exothermic (produces heat, Δ H r = −41 kJ/mol). Methane is also subjected to free-radical chlorination in the production of chloromethanes, although methanol is a more typical precursor. Hydrogen can also be produced via the direct decomposition of methane, also known as methane pyrolysis , which, unlike steam reforming, produces no greenhouse gases (GHG). The heat needed for

3762-431: Is obtained with a completely filled valence shell. This configuration is very stable . For molecules, "open shell" signifies that there are unpaired electrons . In molecular orbital theory, this leads to molecular orbitals that are singly occupied. In computational chemistry implementations of molecular orbital theory, open-shell molecules have to be handled by either the restricted open-shell Hartree–Fock method or

3861-433: Is offset by methane's greater density and temperature range, allowing for smaller and lighter tankage for a given fuel mass. Liquid methane has a temperature range (91–112 K) nearly compatible with liquid oxygen (54–90 K). The fuel currently sees use in operational launch vehicles such as Zhuque-2 and Vulcan as well as in-development launchers such as Starship , Neutron , and Terran R . Natural gas , which

3960-482: Is often approximated as the sum of the energy of each electron, neglecting the electron-electron interactions. The configuration that corresponds to the lowest electronic energy is called the ground state . Any other configuration is an excited state . As an example, the ground state configuration of the sodium atom is 1s  2s  2p  3s , as deduced from the Aufbau principle (see below). The first excited state

4059-416: Is possible to predict most of the exceptions by Hartree–Fock calculations, which are an approximate method for taking account of the effect of the other electrons on orbital energies. Qualitatively, for example, the 4d elements have the greatest concentration of Madelung anomalies, because the 4d–5s gap is larger than the 3d–4s and 5d–6s gaps. For the heavier elements, it is also necessary to take account of

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4158-628: Is quite common to see the letters of the orbital labels (s, p, d, f) written in an italic or slanting typeface, although the International Union of Pure and Applied Chemistry (IUPAC) recommends a normal typeface (as used here). The choice of letters originates from a now-obsolete system of categorizing spectral lines as " s harp ", " p rincipal ", " d iffuse " and " f undamental " (or " f ine"), based on their observed fine structure : their modern usage indicates orbitals with an azimuthal quantum number , l , of 0, 1, 2 or 3 respectively. After f,

4257-557: Is shown in the development of the History of the periodic table and the Octet rule . Niels Bohr (1923) incorporated Langmuir's model that the periodicity in the properties of the elements might be explained by the electronic structure of the atom. His proposals were based on the then current Bohr model of the atom, in which the electron shells were orbits at a fixed distance from the nucleus. Bohr's original configurations would seem strange to

4356-444: Is used. The electron configuration can be visualized as the core electrons , equivalent to the noble gas of the preceding period , and the valence electrons : each element in a period differs only by the last few subshells. Phosphorus, for instance, is in the third period. It differs from the second-period neon , whose configuration is 1s  2s  2p , only by the presence of a third shell. The portion of its configuration that

4455-403: Is usually known as natural gas , which is considered to have an energy content of 39 megajoules per cubic meter, or 1,000 BTU per standard cubic foot . Liquefied natural gas (LNG) is predominantly methane ( CH 4 ) converted into liquid form for ease of storage or transport. Refined liquid methane as well as LNG is used as a rocket fuel , when combined with liquid oxygen , as in

4554-401: Is very long. This is what gives Uranus and Neptune their blue or bluish-green colors, as light passes through their atmospheres containing methane and is then scattered back out. The familiar smell of natural gas as used in homes is achieved by the addition of an odorant , usually blends containing tert -butylthiol , as a safety measure. Methane has a boiling point of −161.5  °C at

4653-542: The Catalytica system , copper zeolites , and iron zeolites stabilizing the alpha-oxygen active site. One group of bacteria catalyze methane oxidation with nitrite as the oxidant in the absence of oxygen , giving rise to the so-called anaerobic oxidation of methane . Like other hydrocarbons , methane is an extremely weak acid . Its p K a in DMSO is estimated to be 56. It cannot be deprotonated in solution, but

4752-492: The German Aufbau , "building up, construction") was an important part of Bohr's original concept of electron configuration. It may be stated as: The principle works very well (for the ground states of the atoms) for the known 118 elements, although it is sometimes slightly wrong. The modern form of the aufbau principle describes an order of orbital energies given by Madelung's rule (or Klechkowski's rule) . This rule

4851-586: The Sabatier process . Methane is also a side product of the hydrogenation of carbon monoxide in the Fischer–Tropsch process , which is practiced on a large scale to produce longer-chain molecules than methane. An example of large-scale coal-to-methane gasification is the Great Plains Synfuels plant, started in 1984 in Beulah, North Dakota as a way to develop abundant local resources of low-grade lignite ,

4950-477: The TQ-12 , BE-4 , Raptor , and YF-215 engines. Due to the similarities between methane and LNG such engines are commonly grouped together under the term methalox . As a liquid rocket propellant, a methane/ liquid oxygen combination offers the advantage over kerosene / liquid oxygen combination, or kerolox, of producing small exhaust molecules, reducing coking or deposition of soot on engine components. Methane

5049-473: The chemical bonds that hold atoms together, and in understanding the chemical formulas of compounds and the geometries of molecules . In bulk materials, this same idea helps explain the peculiar properties of lasers and semiconductors . Electron configuration was first conceived under the Bohr model of the atom , and it is still common to speak of shells and subshells despite the advances in understanding of

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5148-634: The conjugate base is known in forms such as methyllithium . A variety of positive ions derived from methane have been observed, mostly as unstable species in low-pressure gas mixtures. These include methenium or methyl cation CH + 3 , methane cation CH + 4 , and methanium or protonated methane CH + 5 . Some of these have been detected in outer space . Methanium can also be produced as diluted solutions from methane with superacids . Cations with higher charge, such as CH 2+ 6 and CH 3+ 7 , have been studied theoretically and conjectured to be stable. Despite

5247-435: The effects of special relativity on the energies of the atomic orbitals, as the inner-shell electrons are moving at speeds approaching the speed of light . In general, these relativistic effects tend to decrease the energy of the s-orbitals in relation to the other atomic orbitals. This is the reason why the 6d elements are predicted to have no Madelung anomalies apart from lawrencium (for which relativistic effects stabilise

5346-475: The protons and neutrons in the atomic nucleus , as in the shell model of nuclear physics and nuclear chemistry . The form of the periodic table is closely related to the atomic electron configuration for each element. For example, all the elements of group 2 (the table's second column) have an electron configuration of [E]  n s (where [E] is a noble gas configuration), and have notable similarities in their chemical properties. The periodicity of

5445-473: The quantum-mechanical nature of electrons . An electron shell is the set of allowed states that share the same principal quantum number , n , that electrons may occupy. In each term of an electron configuration, n is the positive integer that precedes each orbital letter ( helium 's electron configuration is 1s , therefore n = 1, and the orbital contains two electrons). An atom's n th electron shell can accommodate 2 n electrons. For example,

5544-497: The strength of its C–H bonds, there is intense interest in catalysts that facilitate C–H bond activation in methane (and other lower numbered alkanes ). Methane's heat of combustion is 55.5 MJ/kg. Combustion of methane is a multiple step reaction summarized as follows: Peters four-step chemistry is a systematically reduced four-step chemistry that explains the burning of methane. Given appropriate conditions, methane reacts with halogen radicals as follows: where X

5643-470: The unrestricted Hartree–Fock method. Conversely a closed-shell configuration corresponds to a state where all molecular orbitals are either doubly occupied or empty (a singlet state ). Open shell molecules are more difficult to study computationally. Noble gas configuration is the electron configuration of noble gases . The basis of all chemical reactions is the tendency of chemical elements to acquire stability . Main-group atoms generally obey

5742-406: The 2p orbitals on carbon with various linear combinations of the 1s orbitals on hydrogen. The resulting "three-over-one" bonding scheme is consistent with photoelectron spectroscopic measurements. Methane is an odorless, colourless and transparent gas. It does absorb visible light, especially at the red end of the spectrum, due to overtone bands , but the effect is only noticeable if the light path

5841-419: The 3d-orbital has n  +  l  = 5 ( n  = 3, l  = 2). After calcium, most neutral atoms in the first series of transition metals ( scandium through zinc ) have configurations with two 4s electrons, but there are two exceptions. Chromium and copper have electron configurations [Ar] 3d  4s and [Ar] 3d  4s respectively, i.e. one electron has passed from

5940-432: The 4s-orbital to a 3d-orbital to generate a half-filled or filled subshell. In this case, the usual explanation is that "half-filled or completely filled subshells are particularly stable arrangements of electrons". However, this is not supported by the facts, as tungsten (W) has a Madelung-following d  s configuration and not d  s , and niobium (Nb) has an anomalous d  s configuration that does not give it

6039-561: The Madelung rule are at least close to the ground state even in these anomalous cases. The empty f orbitals in lanthanum, actinium, and thorium contribute to chemical bonding, as do the empty p orbitals in transition metals. Vacant s, d, and f orbitals have been shown explicitly, as is occasionally done, to emphasise the filling order and to clarify that even orbitals unoccupied in the ground state (e.g. lanthanum 4f or palladium 5s) may be occupied and bonding in chemical compounds. (The same

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6138-425: The anomalous configuration [ Og ] 8s 5g 6f 7d 8p , having a p rather than a g electron. Electron configurations beyond this are tentative and predictions differ between models, but Madelung's rule is expected to break down due to the closeness in energy of the 5g, 6f, 7d, and 8p 1/2 orbitals. That said, the filling sequence 8s, 5g, 6f, 7d, 8p is predicted to hold approximately, with perturbations due to

6237-426: The atmosphere. One study reported that the livestock sector in general (primarily cattle, chickens, and pigs) produces 37% of all human-induced methane. A 2013 study estimated that livestock accounted for 44% of human-induced methane and about 15% of human-induced greenhouse gas emissions. Many efforts are underway to reduce livestock methane production, such as medical treatments and dietary adjustments, and to trap

6336-465: The atom. Pauli was able to reproduce Stoner's shell structure, but with the correct structure of subshells, by his inclusion of a fourth quantum number and his exclusion principle (1925): It should be forbidden for more than one electron with the same value of the main quantum number n to have the same value for the other three quantum numbers k [ l ], j [ m l ] and m [ m s ]. The Schrödinger equation , published in 1926, gave three of

6435-403: The basic chemistry of the transition metals . Potassium and calcium appear in the periodic table before the transition metals, and have electron configurations [Ar] 4s and [Ar] 4s respectively, i.e. the 4s-orbital is filled before the 3d-orbital. This is in line with Madelung's rule, as the 4s-orbital has n  +  l  = 4 ( n  = 4, l  = 0) while

6534-679: The breakup of organic matter at elevated temperatures and pressures in deep sedimentary strata . Most methane in sedimentary basins is thermogenic; therefore, thermogenic methane is the most important source of natural gas. Thermogenic methane components are typically considered to be relic (from an earlier time). Generally, formation of thermogenic methane (at depth) can occur through organic matter breakup, or organic synthesis. Both ways can involve microorganisms ( methanogenesis ), but may also occur inorganically. The processes involved can also consume methane, with and without microorganisms. The more important source of methane at depth (crystalline bedrock)

6633-531: The changes in atomic spectra in a magnetic field (the Zeeman effect ). Bohr was well aware of this shortcoming (and others), and had written to his friend Wolfgang Pauli in 1923 to ask for his help in saving quantum theory (the system now known as " old quantum theory "). Pauli hypothesized successfully that the Zeeman effect can be explained as depending only on the response of the outermost (i.e., valence) electrons of

6732-459: The changes of orbital energy with orbital occupations in terms of the two-electron repulsion integrals of the Hartree–Fock method of atomic structure calculation. More recently Scerri has argued that contrary to what is stated in the vast majority of sources including the title of his previous article on the subject, 3d orbitals rather than 4s are in fact preferentially occupied. In chemical environments, configurations can change even more: Th as

6831-477: The chemical properties which must ultimately be explained by a theory of atomic structure. The vast store of knowledge of chemical properties and relationships, such as is summarized by the Periodic Table, should serve as a better foundation for a theory of atomic structure than the relatively meager experimental data along purely physical lines... These electrons arrange themselves in a series of concentric shells,

6930-608: The chosen catalyst. Dozens of catalysts have been tested, including unsupported and supported metal catalysts, carbonaceous and metal-carbon catalysts. The reaction is moderately endothermic as shown in the reaction equation below. As a refrigerant , methane has the ASHRAE designation R-50 . Methane can be generated through geological, biological or industrial routes. The two main routes for geological methane generation are (i) organic (thermally generated, or thermogenic) and (ii) inorganic ( abiotic ). Thermogenic methane occurs due to

7029-588: The cold gas, the gas at ambient temperature is lighter than air. Gas pipelines distribute large amounts of natural gas, of which methane is the principal component. Methane is used as a fuel for ovens, homes, water heaters, kilns, automobiles, turbines, etc. As the major constituent of natural gas , methane is important for electricity generation by burning it as a fuel in a gas turbine or steam generator . Compared to other hydrocarbon fuels , methane produces less carbon dioxide for each unit of heat released. At about 891 kJ/mol, methane's heat of combustion

7128-454: The electron configuration of the neon atom is 1s 2s 2p , meaning that the 1s, 2s, and 2p subshells are occupied by two, two, and six electrons, respectively. Electronic configurations describe each electron as moving independently in an orbital , in an average field created by the nuclei and all the other electrons. Mathematically, configurations are described by Slater determinants or configuration state functions . According to

7227-468: The excitation of valence electrons (such as 3s for sodium) involves energies corresponding to photons of visible or ultraviolet light. The excitation of core electrons is possible, but requires much higher energies, generally corresponding to X-ray photons. This would be the case for example to excite a 2p electron of sodium to the 3s level and form the excited 1s  2s  2p  3s configuration. The remainder of this article deals only with

7326-413: The first shell can accommodate two electrons, the second shell eight electrons, the third shell eighteen, and so on. The factor of two arises because the number of allowed states doubles with each successive shell due to electron spin —each atomic orbital admits up to two otherwise identical electrons with opposite spin, one with a spin + 1 ⁄ 2 (usually denoted by an up-arrow) and one with

7425-429: The first shell containing two electrons, while all other shells tend to hold eight .…» The valence electrons in the atom were described by Richard Abegg in 1904. In 1924, E. C. Stoner incorporated Sommerfeld's third quantum number into the description of electron shells, and correctly predicted the shell structure of sulfur to be 2.8.6. However neither Bohr's system nor Stoner's could correctly describe

7524-476: The four quantum numbers as a direct consequence of its solution for the hydrogen atom: this solution yields the atomic orbitals that are shown today in textbooks of chemistry (and above). The examination of atomic spectra allowed the electron configurations of atoms to be determined experimentally, and led to an empirical rule (known as Madelung's rule (1936), see below) for the order in which atomic orbitals are filled with electrons. The aufbau principle (from

7623-434: The gas to use its combustion energy. Most of the subseafloor is anoxic because oxygen is removed by aerobic microorganisms within the first few centimeters of the sediment . Below the oxygen-replete seafloor, methanogens produce methane that is either used by other organisms or becomes trapped in gas hydrates . These other organisms that utilize methane for energy are known as methanotrophs ('methane-eating'), and are

7722-518: The ground-state configuration, often referred to as "the" configuration of an atom or molecule. Irving Langmuir was the first to propose in his 1919 article "The Arrangement of Electrons in Atoms and Molecules" in which, building on Gilbert N. Lewis 's cubical atom theory and Walther Kossel 's chemical bonding theory, he outlined his "concentric theory of atomic structure". Langmuir had developed his work on electron atomic structure from other chemists as

7821-449: The guts of termites, and the anoxic sediments below the seafloor and the bottom of lakes. This multistep process is used by these microorganisms for energy. The net reaction of methanogenesis is: The final step in the process is catalyzed by the enzyme methyl coenzyme M reductase (MCR). Wetlands are the largest natural sources of methane to the atmosphere, accounting for approximately 20 - 30% of atmospheric methane. Climate change

7920-401: The halogen-to-methane ratio. This reaction is commonly used with chlorine to produce dichloromethane and chloroform via chloromethane . Carbon tetrachloride can be made with excess chlorine. Methane may be transported as a refrigerated liquid (liquefied natural gas, or LNG ). While leaks from a refrigerated liquid container are initially heavier than air due to the increased density of

8019-403: The huge spin-orbit splitting of the 8p and 9p shells, and the huge relativistic stabilisation of the 9s shell. In the context of atomic orbitals , an open shell is a valence shell which is not completely filled with electrons or that has not given all of its valence electrons through chemical bonds with other atoms or molecules during a chemical reaction . Conversely a closed shell

8118-421: The laws of quantum mechanics , a level of energy is associated with each electron configuration. In certain conditions, electrons are able to move from one configuration to another by the emission or absorption of a quantum of energy, in the form of a photon . Knowledge of the electron configuration of different atoms is useful in understanding the structure of the periodic table of elements , for describing

8217-482: The main reason why little methane generated at depth reaches the sea surface. Consortia of Archaea and Bacteria have been found to oxidize methane via anaerobic oxidation of methane (AOM); the organisms responsible for this are anaerobic methanotrophic Archaea (ANME) and sulfate-reducing bacteria (SRB). Given its cheap abundance in natural gas, there is little incentive to produce methane industrially. Methane can be produced by hydrogenating carbon dioxide through

8316-401: The neutral atoms (K, Ca, Sc, Ti, V, Cr, ...) usually follow the order 1s, 2s, 2p, 3s, 3p, 4s, 3d, ...; however the successive stages of ionization of a given atom (such as Fe , Fe , Fe , Fe , Fe) usually follow the order 1s, 2s, 2p, 3s, 3p, 3d, 4s, ... This phenomenon is only paradoxical if it is assumed that the energy order of atomic orbitals is fixed and unaffected by the nuclear charge or by

8415-407: The orbital occupancies have physical significance. For example, the electron configuration of the titanium ground state can be written as either [Ar] 4s  3d or [Ar] 3d  4s . The first notation follows the order based on the Madelung rule for the configurations of neutral atoms; 4s is filled before 3d in the sequence Ar, K, Ca, Sc, Ti. The second notation groups all orbitals with

8514-452: The p 1/2 orbital as well and cause its occupancy in the ground state), as relativity intervenes to make the 7s orbitals lower in energy than the 6d ones. The table below shows the configurations of the f-block (green) and d-block (blue) atoms. It shows the ground state configuration in terms of orbital occupancy, but it does not show the ground state in terms of the sequence of orbital energies as determined spectroscopically. For example, in

8613-442: The periodic table in terms of periodic table blocks is due to the number of electrons (2, 6, 10, and 14) needed to fill s, p, d, and f subshells. These blocks appear as the rectangular sections of the periodic table. The single exception is helium , which despite being an s-block atom is conventionally placed with the other noble gasses in the p-block due to its chemical inertness, a consequence of its full outer shell (though there

8712-501: The presence of electrons in other orbitals. If that were the case, the 3d-orbital would have the same energy as the 3p-orbital, as it does in hydrogen, yet it clearly does not. There is no special reason why the Fe ion should have the same electron configuration as the chromium atom, given that iron has two more protons in its nucleus than chromium, and that the chemistry of the two species is very different. Melrose and Eric Scerri have analyzed

8811-457: The production of chemicals and in food processing. Very large quantities of hydrogen are used in the industrial synthesis of ammonia . At high temperatures (700–1100 °C) and in the presence of a metal -based catalyst ( nickel ), steam reacts with methane to yield a mixture of CO and H 2 , known as "water gas" or " syngas ": This reaction is strongly endothermic (consumes heat, Δ H r = 206 kJ/mol). Additional hydrogen

8910-469: The reaction can also be GHG emission free, e.g. from concentrated sunlight, renewable electricity, or burning some of the produced hydrogen. If the methane is from biogas then the process can be a carbon sink . Temperatures in excess of 1200 °C are required to break the bonds of methane to produce hydrogen gas and solid carbon. However, through the use of a suitable catalyst the reaction temperature can be reduced to between 550-900 °C depending on

9009-489: The s-orbital and the p-orbitals of the same shell have exactly the same energy, to a very good approximation in the absence of external electromagnetic fields. (However, in a real hydrogen atom, the energy levels are slightly split by the magnetic field of the nucleus, and by the quantum electrodynamic effects of the Lamb shift .) The naïve application of the aufbau principle leads to a well-known paradox (or apparent paradox) in

9108-430: The s-orbital of the first shell, so its configuration is written 1s . Lithium has two electrons in the 1s-subshell and one in the (higher-energy) 2s-subshell, so its configuration is written 1s  2s (pronounced "one-s-two, two-s-one"). Phosphorus ( atomic number 15) is as follows: 1s  2s  2p  3s  3p . For atoms with many electrons, this notation can become lengthy and so an abbreviated notation

9207-439: The same atom can have the same values of the four quantum numbers . Physicists and chemists use a standard notation to indicate the electron configurations of atoms and molecules. For atoms, the notation consists of a sequence of atomic subshell labels (e.g. for phosphorus the sequence 1s, 2s, 2p, 3s, 3p) with the number of electrons assigned to each subshell placed as a superscript. For example, hydrogen has one electron in

9306-445: The same value of n together, corresponding to the "spectroscopic" order of orbital energies that is the reverse of the order in which electrons are removed from a given atom to form positive ions; 3d is filled before 4s in the sequence Ti , Ti , Ti , Ti , Ti. The superscript 1 for a singly occupied subshell is not compulsory; for example aluminium may be written as either [Ne] 3s  3p or [Ne] 3s  3p. In atoms where

9405-401: The sequence continues alphabetically g, h, i... ( l  = 4, 5, 6...), skipping j, although orbitals of these types are rarely required. The electron configurations of molecules are written in a similar way, except that molecular orbital labels are used instead of atomic orbital labels (see below). The energy associated to an electron is that of its orbital. The energy of a configuration

9504-451: The total radiative forcing from all of the long-lived and globally mixed greenhouse gases , according to the 2021 Intergovernmental Panel on Climate Change report. Strong, rapid and sustained reductions in methane emissions could limit near-term warming and improve air quality by reducing global surface ozone. Methane has also been detected on other planets, including Mars , which has implications for astrobiology research. Methane

9603-467: The transition metals, the 4s orbital is of a higher energy than the 3d orbitals; and in the lanthanides, the 6s is higher than the 4f and 5d. The ground states can be seen in the Electron configurations of the elements (data page) . However this also depends on the charge: a calcium atom has 4s lower in energy than 3d, but a Ca cation has 3d lower in energy than 4s. In practice the configurations predicted by

9702-418: Was first stated by Charles Janet in 1929, rediscovered by Erwin Madelung in 1936, and later given a theoretical justification by V. M. Klechkowski : This gives the following order for filling the orbitals: In this list the subshells in parentheses are not occupied in the ground state of the heaviest atom now known ( Og , Z  = 118). The aufbau principle can be applied, in a modified form, to

9801-451: Was lower than expected initially, due to the rupture of a dam in the town of Świniary under Plock iem. During the flood Vistula May 22, 2014 r. To Włocławski Reservoir affect 4900 m³/s, the discharge was at that time 4300 m³/s. As a result, they managed to flatten the wave of flood and reduce the risk of flooding in the lower section of the Vistula. This Poland location article is

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