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Topic: Delocalised electron

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	NationMaster - Encyclopedia: Delocalised electron
		In chemistry, delocalized electrons are electrons in a molecule that do not belong to a single atom or a covalent bond.
		In physics delocalized electrons are electrons in a molecule that are not associated with a single atom or a covalent bond.
		Electron density is the measure of the probability of an electron being present at a specific location.
	www.nationmaster.com /encyclopedia/Delocalised-electron (289 words)

	Delocalized electron - Wikipedia, the free encyclopedia
		In physics delocalized electrons are electrons in a molecule that are not associated with a single atom or a covalent bond.
		A case of delocalized electrons occurs also in solid metals, where the d-subshell interferes with the above s-subshell, and contributes to the properties of a metal.
		This means that the electrons are free to move throughout the structure, and gives rise to properties such as conductivity.
	en.wikipedia.org /wiki/Delocalised (290 words)

	Electron density - Wikipedia, the free encyclopedia
		Electron density is the measure of the probability of an electron being present at a specific location.
		In delocalised or conjugated systems, such as phenol and benzene (and compounds such as haemoglobin and chlorophyll) the electron density covers an entire region, i.e., in benzene they are found above and below the planar ring.
		Electron densities are sometimes probed with X-ray diffraction scans, where X-rays of a suitable wavelength are targeted towards a sample and measurements are made over time to represent, probabilistically, where electrons can be found.
	en.wikipedia.org /wiki/Electron_density (315 words)

	Electronic Properties
		Electrons in solids are in localized or delocalized states, levels, or orbitals.
		Electrons are bound to atoms and corrections are added for overlap of the electron density produced by different atoms.
		The finite wavelength of the electrons causes Friedel oscillations in the electron density near the surface (this is analogous to what happens when one tries to express a step function as a sum of sinusoidal functions up to a maximum frequency).
	www.virginia.edu /ep/SurfaceScience/electron.html (2062 words)

	Delocalized electron - Biocrawler (Site not responding. Last check: 2007-10-14)
		In chemistry, delocalized electrons are electrons in a molecule that do not belong to a single atom or a covalent bond.
		Delocalized electrons can be found in conjugated systems of double bonds and in aromatic systems.
		Delocalized electrons are important to take into account for several reasons.
	www.biocrawler.com /encyclopedia/Delocalised (283 words)

	Electron Summary
		Our understanding of how electrons behave has been significantly modified during the past century, the greatest advances being the development of quantum mechanics in the 20th century and the idea of particle-wave duality, that is, that electrons show either wave-like or particle-like properties.
		Electrons in an atom are bound to that atom; electrons moving freely in vacuum, space or certain media are free electrons that can be focused into an electron beam.
		The antimatter counterpart of the electron is the positron.
	www.bookrags.com /Electron (7793 words)

	Science -- Bardeen 293 (5529): 444
		An electron is arguably the simplest possible reactant in a condensed phase environment because it lacks the intramolecular vibrational modes of a molecular solute.
		Electrons in immediate contact pairs will leave when the control pulse is applied, but some solvent-separated pairs recombine with the sodium atom.
		Electrons that originally stayed close to home in immediate contact pairs will leave when the control pulse is applied, but some that originally ventured farther afield in solvent-separated pairs can be persuaded to return more quickly.
	www.chem.ucla.edu /dept/Faculty/schwartz/schwartz_press/Science.293.444.2001.html (983 words)

	Goldhaber-Gordon Group \| Department of Physics \| Stanford University
		Electron flow from one lead to the other through the magnetic impurity serves as a powerful probe of the local electronic states.
		Using both electron beam and optical lithography, metal gates are patterned on the insulating surface of the heterostructure (annealed ohmic contacts to the 2DEG are fabricated in an earlier lithography step).
		Since electrons could be added to the system one at a time, the impurity could be converted from even occupancy (paired electrons and thus non-magnetic) to odd occupancy (unpaired electron and thus magnetic).
	www.stanford.edu /group/GGG/kondo.html (1307 words)

	Why are plants green? Why are flamingos pink? (organic compounds)
		These electrons, no longer localized in a double bond between two adjacent atoms, are now free to range over the whole molecule and hence are "delocalized." This electron delocalization stabilizes the molecule.
		The existence of electrons in molecular orbitals is one requirement for color.
		Such delocalised polyenes have very strong absorption bands in the visible regions of the spectrum, allowing the plant to absorb the energy from sunlight.
	webexhibits.org /causesofcolor/7.html (1983 words)

	NationMaster - Encyclopedia: Delocalised
		In chemical compounds, delocalised electrons do not belong strictly to a covalent bond or single atom, but move more freely between the parts of the compound.
		One particular example is the benzene ring, where the central ring of carbon atoms leaves three electrons delocalised.
		This is presented either by drawing oscillating double bonds, or simply marking a circle in the benzene ring.
	www.nationmaster.com /encyclopedia/Delocalised (195 words)

	Research Group of Jorge H. Rodriguez
		Recent experiments suggest that electronic spin can be used to control and manipulate the electrical conductivity and other properties of potential molecular-based electronic devices.
		We are studying the electronic structure of nanotube models to establish some correlations between their geometric structures, density of states (DOS), and characteristics of their valence and conduction bands.
		The one-electron density spans the entire nanostructure indicating that the molecular geometry allows, by itself, intrinsic delocalization whereby some valence electrons are completely delocalized along the axis of the nanotube.
	www.physics.purdue.edu /biomolecular_physics/molecular_spintronics.shtml (702 words)

	Ultrafast Surface Dynamics Group - Prof. Dr. Martin Wolf
		A single electron in a polar environment like water is one of the simplest systems to figure the process of solvation: The localized electron attracts the positively charged ends of the polar solvent molecules, thus inducing a reorientation of the molecules to screen the electron, which results in an energy gain.
		An ideal candidate to investigate the phenomenon of electron solvation is the photoinjection of an electron into an ice layer adsorbed on a metal surface and to monitor the evolution of the electron's energy in real time by fs time-resolved photoelectron spectroscopy.
		The shielding of the electron wavefunction due to the solvation is expected to have consequences on the lifetime of the electron in the ice layer, which is indirectly proportional to the overlap of the wavefunctions of the electron in the ice and unoccupied metal states.
	www.physik.fu-berlin.de /~femtoweb/newfemtos/eldyn/elocsolv.php (1960 words)

	Chem - Option H - Further organic chemistry
		This causes the electrons from the H-Cl bond to be moved onto the Cl atom.
		If an electron withdrawing group (such as a halogen) is connected to the delta +ve carbon being attacked, then the delta +ve charge will be increased, resulting in a greater rate of nucleophillic substitution.
		These are very weak bases due to the electron withdrawing effect of the C=O group, which reduces the negative charge on the N atom, making it less able to attract protons, and less stable once it has one.
	homepage.mac.com /stray/ib/chem/Options/organic.html (2278 words)

	Rearrangement
		Since this is a two-electron process (the 2 electrons in the relocated sigma bond), the rearrangement is predicted to be suprafacial.
		The source of this assistance was proposed to be the electron pair of the C1 : C6 sigma bond, which is ideally oriented anti to the sulfonate leaving group.
		An electron deficient nitrogen atom does not have to be a cation, as the nitrene example on the right (green box) demonstrates.
	www.cem.msu.edu /~reusch/VirtualText/rearrang.htm (7059 words)

	The Benzene Problem
		Definition: Delocalised electron systems in organic molecules involve p bonds with all the carbon (or other) atoms in the system in a single plane and in which overlap of p orbitals extends over a significant number of carbon atoms.
		Delocalised systems are highly saturated, but their reactions are of substitution rather than addition..
		This represents the delocalised electrons, and is probably the best way of representing the delocalisation during mechanisms.
	www.webchem.net /notes/A2/crs/benzene_problem.htm (558 words)

	Glossary of Terms for Computational Chemistry
		Representation of the electron cloud surrounding an atom.
		Electrons which do not reside along a single bond, but move from bond to bond, as in an aromatic carbon bond.
		A measure of the "thickness" of the electron cloud in a given place, eg, the probability of the electron's presence.
	www.shodor.org /chemviz/glossary.html (1468 words)

	Electric circuits \|\| Potential energy
		Electrons at the negative end are at a higher potential energy than the positive end.
		The potential energy of an electron at any point along the wire is determined by the concentration of the delocalised electrons at that point.
		As an electron moves along the wire its potential energy decreases in the same way that a ball loses potential energy as is rolls down a gravitational hill (and increases in kinetic energy).
	www.dur.ac.uk /p.m.johnson/electric_circuits/05_potential_energy.htm (458 words)

	1
		The outer shell electrons of a metal (the valence electrons) are relatively easily removed, with the formation of metal cations.
		Since the bonding in metals stems from the attraction of the metal cations to the delocalised electrons, it is not surprising that moving from sodium (one outer electron) through magnesium (two outer electrons) to aluminium (three outer electrons) the bonding gets gradually stronger.
		Some electron density is concentrated between the ions and the bond begins to resemble a covalent bond in which an electron pair is localised between two atoms.
	home.freeuk.net /braybrook/6-1/Foundation/bonding_and_structure.htm (5011 words)

	Slides22a
		Two are in the bonding orbital and yield a bond order of 0.5, which when added to the sigma bond corresponds to a bond order of 1.5 between each of the oxygens.
		The placement of all 16 valence electrons is indicated.
		C=CH-CH-CH The average carbon-carbon bondlength (C=C and C-C) is 142 pm and allows calculation of the wavelength of the absorbed light by using the particle-in-a-box to estimate the energy levels.
	www.andrew.cmu.edu /course/09-105/S98Slides22a.html (537 words)

	General Chemistry Online: FAQ: Chemical bonds: Why are free radicals so reactive?
		Electrons repel, and forcing them into the same region of space raises their energy.
		And adding electrons to an antibonding orbital raises the energy of the molecule relative to that of the separated atoms.
		Several resonance structures mean the odd electron is delocalized and contributes to the overall binding (and stability) of the molecule.
	antoine.frostburg.edu /chem/senese/101/bonds/faq/why-are-free-radicals-reactive.shtml (528 words)

	Pairs The - oxygensupplement.info - ... (Site not responding. Last check: 2007-10-14)
		The 14 remaining electrons should absorption of solar radiation by collision pairs of oxygen is a small but significant part of the total budget of incoming shortwave radiation.
		Two electrons not involved in the covalent bonds are called lone pair electrons.
		This requires the delocalizing n electron pair on the ether oxygen to occupy a p orbital like orientation ortho to the plane of the carbonyl group.
	www.oxygensupplement.info /and_nitrogen/pairs_the (927 words)

	Chemblog (Site not responding. Last check: 2007-10-14)
		This is usually considered to be because electrons are free to cycle around circular arrangements of atoms, which are alternately single- and double-bonded to one another.
		Thus, there are not enough electrons to form double bonds on all the carbon atoms, but the "extra" electrons strengthen all of the bonds on the ring equally.
		Whereas benzene is aromatic (6 electrons, from 3 double bonds), cyclobutadiene is not, since the number of π delocalized electron is 4, which is not satisfied by any n integer value.
	chemblog.chemicalblogs.com /33_chemblog (1491 words)

	Polymer Electronics Polymers Organic electronics Polymerelectronics PolyIC Polymer-Electronics
		With the deployment of such materials for electronic applications, the words "polymer electronics" were shaped.
		Although the generic term "polymer electronics" is often used, the electronic features are not limited to polymers - which means to large molecule chains - but also include "small molecules".
		With this process, it will be possible to fabricate low-cost electronics in a continuous printing process on flexible substrate, more or less similar to the printing process of newspapers.
	www.polyic.com /en/polymer-electronics.php (562 words)

	Graphite's delocalised electron? (Site not responding. Last check: 2007-10-14)
		They say 3 of graphite's electrons are covalently bonded and the other one is delocalised.
		Actually the electrons forms an entire molecular bond, that is, it is effectively delocalized in all the molecule, that is, the electronic "cloud" is made of two doghnuts over the plane of the molecule, on opposite sides.
		In graphite, all the Benzene rings become one, in this sense: the electrons are delocalized in all the plane of the molecules, above and under.
	www.physicsforums.com /showthread.php?threadid=147222 (511 words)

	Lumex Opto/Components -- Electronic Polymers (Site not responding. Last check: 2007-10-14)
		These are polymers which possess a delocalised pi-electron system along the polymer backbone; the delocalised pi-electron system confers semiconducting properties to the polymer and gives it the ability to support positive and negative charge carriers with high mobilities along the polymer chain.
		In the example shown the cyano group is electron withdrawing and therefore pushes down the barrier to electron injection.
		It is not primarily a replacement for existing electronic technologies, but opens up a spectre of completely new applications that combine the features of transistor, LED,detector and interconnect devices with the form factor, flexibility, and low cost of plastics.
	www.lumex.com /tech_notes/polymer.html (1675 words)

	StainsFile - Structure and Colour in Dyes
		Rather, chromophores function by altering the energy in the delocalised electron cloud of the dye, and this alteration results in the compound absorbing radiation from within the visible range instead of outside it.
		By incorporating the delocalised electrons in these configurations into the delocalised electrons in the aryl rings of aromatic compounds, the energy contained in the electron cloud can be modified.
		Any delocalised electrons and their energy can simply be added to that already present, thus increasing it.
	stainsfile.info /StainsFile/dyes/dyecolor.htm (2800 words)

	[LEPs] - The Chemistry of LEPs (Site not responding. Last check: 2007-10-14)
		The electron injector needs to inject electrons of sufficient energy to exceed the band gap, the anode operates by removing electrons from the polymer and consequently leaving regions of positive charge called holes.
		It is logical for an electron to fill a hole when the opportunity is presented and they are said to capture one another.
		When captured, an electron and a hole form neutral-bound excited states (termed excitons) that quickly decay and produce a photon up to 25% of the time, 75% of the time, decay produces only heat, this is due to the the possible multiplicities of the exciton.
	www.methylblue.com /detritus/LEPs/chemistry.html (758 words)

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