Electron density
237630
196330460
2008-03-06T18:09:37Z
Vossman
250800
/* See also */ +Resolution (electron density)
{{otheruses4|the quantum mechanical probability density of an electron|the number density of electrons in a plasma|Plasma (physics)}}
'''Electron density''' is the measure of the [[probability]] of an [[electron]] being present at a specific location.
In [[molecule]]s, regions of electron density are usually found around the [[atom]], and its bonds. In de-localized or [[conjugated system]]s, such as [[phenol]], [[benzene]] and compounds such as [[hemoglobin]] and [[chlorophyll]], the electron density covers an entire region, i.e., in benzene they are found above and below the planar ring. This is sometimes shown diagrammatically as a series of alternating single and double bonds. In the case of phenol and benzene, a circle inside a [[hexagon]] shows the de-localized nature of the compound. This is shown below:
[[Image:Phenol mesomeric structures.png|503px|center|Mesomeric structures of phenol]]
In compounds with multiple ring systems which are interconnected, this is no longer accurate, so alternating single and double bonds are used. In compounds such as chlorophyll and phenol, some diagrams show a dotted or dashed line to represent the de-localization of areas where the electron density is higher next to the single bonds <ref>e.g., the white line in the diagram on [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Chlorophyll.html Chlorophylls and Carotenoids]</ref>. Conjugated systems can sometimes represent regions where [[electromagnetic radiation]] is absorbed at different wavelengths resulting in compounds appearing coloured. In [[polymer]]s, these areas are known as chromophores.
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. [[Quantum electrodynamics]] and some branches of [[Quantum field theory|quantum theory]] also study and analyze electron [[superposition]] and other phenomena. [[Quantum tunneling]] and [[quantum entanglement]] are interesting areas involving [[electron]]s (or [[photon]]s). High speed electrons are often used in transmission electron micrography (or microscopy, [[TEM]]) and deep [[inelastic scattering]], as well as many other high-speed particle experiments involving electrons.
[[Mulliken population analysis]] is based on electron densities in molecules and is a way of dividing the density between atoms to give an estimate of atomic charges.
==Spin density==
'''Spin density''' is electron density applied to [[free radical]]s. It is defined as the total electron density of electrons of one spin minus the total electron density of the electrons of the other spin. One of the ways to measure it experimentally is by [[electron spin resonance]] <ref>IUPAC [[Gold Book]][http://www.iupac.org/goldbook/S05864.pdf Link]</ref>.
== See also ==
*[[Electron configuration]]
*[[Electron cloud]]
*[[Resolution (electron density)]]
==References==
<references/>
[[Category:Quantum chemistry]]
[[Category:Electron]]
[[de:Elektronendichte]]
[[es:Densidad (mecánica cuántica)]]
[[fr:Densité électronique]]
[[it:Densità elettronica]]
[[pl:Gęstość elektronowa]]
[[ru:Электронная плотность]]