Difference between revisions of "Electron" - New World Encyclopedia

From New World Encyclopedia
 
m
(29 intermediate revisions by 7 users not shown)
Line 1: Line 1:
{{alternateuses}}
+
{{2Copyedited}}{{Ebcompleted}}{{Copyedited}}{{Paid}}{{Approved}} {{Images OK}} {{Status}}  {{Submitted}}
 
{| border="1" cellspacing="0" align="right" cellpadding="2" style="margin-left:1em"
 
{| border="1" cellspacing="0" align="right" cellpadding="2" style="margin-left:1em"
 
|-
 
|-
Line 32: Line 32:
 
|-
 
|-
 
|Mass:  
 
|Mass:  
| 9.109 3826(16)&nbsp;×&nbsp;10<sup>&minus;31</sup>&nbsp;[[Kilogram|kg]]
+
| 9.109 3826(16)&nbsp;×&nbsp;10<sup>&minus;31</sup>&nbsp;kg
 
|-
 
|-
 
|
 
|
Line 40: Line 40:
 
| 0.510 998 918(44)&nbsp;[[MeV]]/[[speed of light|c]]<sup>2</sup>{{inote|http://scienceworld.wolfram.com/physics/ElectronMass.html}}
 
| 0.510 998 918(44)&nbsp;[[MeV]]/[[speed of light|c]]<sup>2</sup>{{inote|http://scienceworld.wolfram.com/physics/ElectronMass.html}}
 
|-
 
|-
|[[Elementary charge|Electric Charge]]:  
+
|[[Electric Charge]]:  
 
| &minus;1.602 176 53(14)&nbsp;×&nbsp;10<sup>&minus;19</sup>&nbsp;[[Coulomb|C]]
 
| &minus;1.602 176 53(14)&nbsp;×&nbsp;10<sup>&minus;19</sup>&nbsp;[[Coulomb|C]]
 
|-
 
|-
Line 50: Line 50:
 
|-
 
|-
 
|Interaction:  
 
|Interaction:  
| [[Gravity]], [[Electromagnetic interaction|Electromagnetic]], <br>[[Weak interaction|Weak]]
+
|[[Gravity]], [[Electromagnetic interaction|Electromagnetic]], <br/>[[Weak interaction|Weak]]
 
|}
 
|}
 
|}
 
|}
The '''electron''' is a fundamental [[subatomic particle]] which carries a negative [[electric charge]]. Within an [[atom]] the electrons surround the [[atomic nucleus|nucleus]] of [[proton]]s and [[neutron]]s in an [[electron configuration]]. The word ''electron'' was coined in [[1894]] and is derived from the term ''electric'', whose ultimate origin is the [[Greek language|Greek]] word '&eta;&lambda;&epsilon;&kappa;&tau;&rho;&omicron;&nu;, meaning ''[[amber]]''.  [[Electrostatic charge]] can be generated by rubbing amber with the pelt of an animal such as a cat. The ending ''-on'', shared by most subatomic particles, was used in analogy to the word ''[[ion]]''.
+
The '''electron''' is a fundamental [[subatomic particle]], which carries a negative [[electric charge]]. Electrons generate an [[electric field]]. In organized motion they constitute [[electric current]] and generate a [[magnetic field]]. Electric current over time is a form of energy ([[electricity]]) that may be harnessed as a practical means to perform work. Electrons are found within [[atom]]s and surround the [[atomic nucleus|nucleus]] of [[proton]]s and [[neutron]]s in a particular [[electron configuration]]. It is the electonic configuration of atoms that determines an [[Chemical element|element]]’s physical and chemical properties. The exchange or sharing of electrons constitute [[chemical bond]]s, and they are thus important in demonstrating the relational nature of physical existence.
 +
{{toc}}
 +
The word ''electron'' was coined in 1894 and is derived from the term “electric,whose ultimate origin is the [[Greek language|Greek]] word '&eta;&lambda;&epsilon;&kappa;&tau;&rho;&omicron;&nu;, meaning ''amber''.  
  
Electrons in motion constitute [[electric current]] which may be used by scientists and engineers to measure many physical properties.  Electric current over time is a form of energy ([[electricity]]) that may be harnessed as a practical means to perform work. 
+
==Characteristics==
  
The variations in [[electric field]] generated by differing numbers of electrons and their configurations in atoms determine the chemical properties of the [[element]]s.  These fields play a fundamental role in [[chemical bond]]s and [[chemistry]].
+
The electron is one of a class of subatomic particles called [[lepton]]s which are believed to be [[particle physics|fundamental particles]]. As an [[elementary particle]] it is not considered to have any substructure (at least, experiments have not found any so far) and there is good reason to believe that there is not any. Hence, it is usually described as point-like, i.e. with no spatial extension. However, if one gets very near an electron, one notices that its properties ([[charge]] and [[mass]]) seem to change. This is an effect common to all elementary particles: the particle influences the [[vacuum fluctuation]]s in its vicinity, so that the properties one observes from far away are the sum of the bare properties and the [[vacuum]] effects (see [[renormalization]]).
  
==Electrons in practice ==
+
The [[antimatter]] counterpart of the electron is its antiparticle, the [[positron]].
===Classification of electrons===
 
  
The electron is one of a class of subatomic particles called [[lepton]]s which are believed to be [[particle physics|fundamental particles]] (that is, they cannot be broken down into smaller constituent parts). The word "particle" is somewhat misleading however, because [[quantum mechanics]] shows that electrons also behave like a wave, e.g. in the [[double-slit experiment]]; this is called [[wave-particle duality]].
+
Charged particles, monatomic [[ion]]s and larger particles, arise from an imbalance in the total number of electrons and [[protons]] in the particle. When there is an excess of electrons, the object is said to be negatively charged. When there are fewer electrons than [[proton]]s, the object is said to be positively charged. When the number of electrons and the number of protons are equal, the object is said to be electrically neutral. A macroscopic body can acquire charge through rubbing, i.e. the phenomena of [[triboelectricity]].  
  
The antiparticle of an electron is the '''[[positron]]''', which has the same mass but positive rather than negative charge. The term '''negatron''' is sometimes used to refer to standard electrons so that the term ''electron'' may be used to describe both positrons and negatrons, as proposed by [[Carl David Anderson|Carl D. Anderson]]. Under ordinary circumstances, however, ''electron'' refers to the negatively charged particle alone.
+
Electrons have a negative [[electric charge]] of &minus;1.6&nbsp;×&nbsp;10<small><sup>&minus;19</sup></small>&nbsp;[[coulomb]]s (this is usually just stated as a charge of &minus;1) and a mass of about 9.11&nbsp;×&nbsp;10<small><sup>&minus;31</sup></small>&nbsp;kilograms (0.51&nbsp;MeV/c<sup>2</sup>), which is approximately <sup>1</sup>&#8260;<sub>1836</sub> of the mass of the [[proton]]. These are commonly represented as '''e<sup>&minus;</sup>'''. The electron has [[spin (physics)|spin]] ½, which implies it is a [[fermion]], i.e., it follows the [[Fermi-Dirac statistics]]. While most electrons are found in atoms, others move independently in matter, or together as an [[electron beam]] in a [[vacuum]]. In some [[superconductor]]s, electrons move in Cooper pairs, in which their motion is coupled to nearby matter via lattice vibrations called phonons. When electrons move, free of the nuclei of atoms, and there is a net flow of charge, this flow is called [[electricity]], or an [[electric current]]. There is also a physical constant called the [[classical electron radius]], with a value of 2.8179&nbsp;×&nbsp;10<sup>&minus;15</sup> meters. Note that this is the radius that one could infer from its charge if the physics were only described by the [[classical electromagnetism|classical]] theory of [[electrodynamics]] and there were no [[quantum mechanics]] (hence, it is an outdated concept that nevertheless sometimes still proves useful in calculations).
  
 +
==Electrons in theory==
  
===Properties and behavior of electrons===
+
As applied to electrons the word "particle" is somewhat misleading. This is because electrons can also behave like a wave; that is they exhibit wave-particle duality. The wave behavior of electrons can be demonstrated in the interference patterns produced in a double-slit experiment, and is employed in the [[electron microscope]]. The wave nature of electrons is essential to the [[quantum mechanics]] of the electromagnetic interaction, where electrons are represented by [[wavefunction]]s. From the square of the wavefunction the [[electron density]] can be determined. Also, the exact momentum and position of an electron cannot be simultaneously determined. This is a limitation described by the Heisenberg uncertainty principle, which, in this instance, simply states that the more accurately we know a particle's position, the less accurately we can know its momentum and vice versa.  
 
 
Electrons have a negative [[electric charge]] of &minus;1.6&nbsp;×&nbsp;10<small><sup>&minus;19</sup></small>&nbsp;[[coulomb]]s, and a mass of about [[1 E-31 kg|9.11&nbsp;×&nbsp;10<small><sup>&minus;31</sup></small>&nbsp;kg]] (0.51&nbsp;MeV/c<sup>2</sup>), which is approximately <sup>1</sup>&#8260;<sub>1836</sub> of the mass of the [[proton]]. These are commonly represented as '''e<sup>&minus;</sup>'''.
 
 
 
According to [[quantum mechanics]], electrons can be represented by [[wavefunction]]s, from which the [[electron density]] can be determined. The exact momentum and position of an electron cannot be simultaneously determined. This is a limitation described by the [[Heisenberg uncertainty principle]], which, in this instance, simply states that the more accurately we know a particle's position, the less accurately we can know its momentum and vice versa.
 
 
 
The electron has [[spin (physics)|spin]] ½, which implies it is a [[fermion]], i.e., it follows the [[Fermi-Dirac statistics]]. While most electrons are found in atoms, others move independently in matter, or together as an [[electron beam]] in a [[vacuum]].  In some [[superconductor]]s, electrons move in Cooper pairs, in which their motion is coupled to nearby matter via lattice vibrations called phonons. When electrons move, free of the nuclei of atoms, and there is a net flow, this flow is called [[electricity]], or an [[electric current]].
 
 
 
A body has a static charge, when the body that has more or fewer electrons than are required to balance the positive charge of the nuclei.  When there is an excess of electrons, the object is said to be negatively charged. When there are fewer electrons than [[proton]]s, the object is said to be positively charged. When the number of electrons and the number of protons are equal, the object is said to be electrically neutral. A macroscopic body can aquire charge through rubbing, i.e. the phenomena pf [[triboelectricity]]. Electrons and [[positron]]s can [[electron-positron annihilation|annihilate]] each other and produce a pair of [[photons]]. Conversely, a high-energy photon can be transformed into an electron and a positron by a process called [[pair production]].
 
 
 
The electron is an [[elementary particle]]&mdash; that means that it has no [[substructure]] (at least, experiments have not found any so far, and there is good reason to believe that there is not any). Hence, it is usually described as [[point]]-like, i.e. with no spatial extension. However, if one gets very near an electron, one notices that its properties ([[charge]] and [[mass]]) seem to change. This is an effect common to all elementary particles: the particle  influences the [[vacuum fluctuation]]s in its vicinity, so that the properties one observes from far away are the sum of the bare properties and the vacuum effects (see [[renormalization]]).
 
 
 
There is a physical constant called the [[classical electron radius]], with a value of 2.8179&nbsp;×&nbsp;10<sup>&minus;15</sup> [[Metre|m]]. Note that this is the radius that one could infer from its charge if the physics were only described by the [[classical electromagnetism|classical]] theory of [[electrodynamics]] and there were no [[quantum mechanics]] (hence, it is an outdated concept that nevertheless sometimes still proves useful in calculations).
 
 
 
The speed of an electron in a [[vacuum]] can approach, but never reach c, the [[speed of light]] in a [[vacuum]]. This is due to an effect of [[special relativity]].  The effects of [[special relativity]] are based on a quantity known as gamma or the [[Lorentz factor]]. Gamma is a function of v, the velocity of the particle, and c. The following is the formula for gamma:
 
 
 
:<math>\gamma = 1 / \sqrt{1 - (v^2/c^2)}</math>
 
 
 
The energy necessary to accelerate a particle is gamma minus one times the rest mass. For example, the [[linear accelerator]] at [[Stanford]] can [http://www2.slac.stanford.edu/vvc/theory/relativity.html accelerate] an electron to roughly 51&nbsp;GeV. This gives you a gamma of 100,000 given that the rest mass of an electron is 0.51&nbsp;MeV/c² (the [[relativistic mass]] of this fast electron is 100 000 times its rest mass). Solving the equation above for the speed of the electron gives a speed of:
 
 
 
:<math>(1-\frac {1} {2} \gamma ^{-2})c</math> = 0.999&nbsp;999&nbsp;999&nbsp;95&nbsp;c.
 
 
 
(The formula applies for large &gamma;.)
 
 
 
===Electrons in the universe===
 
It is believed that the number of electrons existing in the known [[universe]] is at least 10<sup>79</sup>. This number amounts to a density of about one electron per [[cubic metre]] of space.
 
 
 
Based on the [[classical electron radius]] and assuming a dense [[sphere packing]], it can be calculated that the number of electrons that would fit in the [[observable universe]] is on the order of 10<sup>130</sup>. Of course, this number is even less  meaningful than the classical electron radius itself.
 
 
 
===Electrons in industry===
 
 
 
[[Electron beam]]s are used in [[electron beam welding|welding]] as well as [[electron beam lithography|lithography]].
 
 
 
==Electrons in the laboratory==
 
===Founding experiments===
 
The quantum or discrete nature of electron's charge was observed by [[Robert Millikan]] in the [[Oil-drop experiment]] of [[1909]].
 
 
 
===Use of electrons in the laboratory===
 
[[Electron microscope]]s are used to magnify details up to 500,000 times.  Quantum effects of electrons are used in [[Scanning tunneling microscope]] to study features at the atomic scale.
 
 
 
==Electrons in theory==
 
In relativistic[[quantum mechanics]], the electron is described by the [[Dirac Equation]]. In the [[Standard Model]] of [[particle physics]], it forms a doublet in SU(2) with the [[electron neutrino]], as they interact through the [[weak interaction]]. The electron has two more massive partners, with the same charge but different masses: the [[muon]] and the [[tauon]].
 
  
The [[antimatter]] counterpart of the electron is its antiparticle, the [[positron]]. The positron has the same amount of electrical charge as the electron, except that the charge is positive. It has the same mass and spin as the electron. When an electron and a positron meet, they may [[Annihilation|annihilate]] each other, giving rise to two [[Gamma ray|gamma-ray]] photons, each having an energy of 0.511 [[MeV]] (511 [[keV]]). See also [[Electron-positron annihilation]].  
+
In relativistic [[quantum mechanics]], the electron is described by the [[Dirac Equation]]. [[Quantum electrodynamics]] (QED) models an electron as a charged particle surrounded a sea of interacting [[virtual particles]], modifying the sea of virtual particles which makes up a vacuum. Treating the electron as a dimensionless point, however, gives calculations that produce infinite terms. In order to remove these infinities a practical (although mathematically dubious) method called [[renormalization]] was developed whereby infinite terms can be cancelled to produce finite predictions about the electron. The correction of just over 0.1 percent to the predicted value of the electron's gyromagnetic ratio from exactly 2 (as predicted by Dirac's single particle model), and it's extraordinarily precise agreement with the experimentally determined value is viewed as one of the pinnacles of modern physics. There are now indications that [[string theory]] and its descendants may provide a model of the electron and other fundamental particles where the infinities in calculations do not appear, because the electron is no longer seen as a dimensionless point. At present, string theory is very much a 'work in progress' and lacks predictions analogous to those made by QED that can be experimentally verified.
  
Electrons are also a key element in [[electromagnetism]], an approximate theory that is adequate for macroscopic systems, and for classical modelling of microscopic systems.
+
In the Standard Model of [[particle physics]] there are three generations of matter particles. In this model the [[muon]] and the [[tauon]] correspond to the electron in the other two generations. Also in the model each fundamental particle has an antiparticle counterpart. The antiparticle of the electron is the positron (see below). Electrons are also a key element in [[electromagnetism]], an approximate theory that is adequate for macroscopic systems, and for classical modeling of microscopic systems.
  
 
==History==
 
==History==
The electron as a unit of charge in electrochemistry had been posited by [[G. Johnstone Stoney]] in [[1874]]. In [[1894]], he also invented the word itself.
+
The electron has a special place in the history of understanding matter. It was the first subatomic particle to be discovered and was important in the development of [[quantum mechanics]]. As a unit of charge in electrochemistry it was posited by [[G. Johnstone Stoney]] in 1874. In 1894, he also invented the word itself.
  
The discovery that the electron was a [[subatomic particle]] was made in [[1897]] by [[J.J. Thomson|J.J. Thomson]] at the [[Cavendish Laboratory]] at [[University of Cambridge|Cambridge University]], while he was studying "[[cathode rays]]". Influenced by the work of [[James Clerk Maxwell]], and the discovery of the [[X-ray]], he deduced that [[cathode ray tube|cathode ray]]s existed and were negatively charged "''particles''", which he called "''corpuscles''". He published his discovery in [[1897]].
+
The discovery that the electron was a [[subatomic particle]] was made in 1897 by [[J.J. Thomson]] at the Cavendish Laboratory at [[University of Cambridge|Cambridge University]], while he was studying "[[cathode ray]]s." Influenced by the work of [[James Clerk Maxwell]], and the discovery of the [[X-ray]], he deduced that [[cathode ray tube|cathode ray]]s existed and were negatively charged "''particles''," which he called "''corpuscles''." He published his discovery in 1897. Thomson's work only allowed him to determine charge to mass ratio of the electron. It was Millikan's [[oil-drop experiment]] of 1909 that measured the charge on the electron and thus allowed calculation of its mass.
  
The [[periodic law]] states that the chemical properties of elements largely repeat themselves periodically and is the foundation of the [[periodic table]] of elements. The law itself was initially explained by the [[atomic mass]] of the elements. However, as there were anomalies in the periodic table, efforts were made to find a better explanation for it. In [[1913]], [[Henry Moseley]] introduced the concept of the [[atomic number]] and explained the [[periodic law]] with the number of protons each element has. In the same year, [[Niels Bohr]] showed that electrons are the actual foundation of the table. In [[1916]], [[Gilbert Newton Lewis]] and [[Irving Langmuir]] explained the chemical bonding of elements by electronic interactions.
+
The first quantum mechanical theories were explanations of the electronic stucture of atoms. In 1913 [[Neils Bohr]] proposed the first quantum mechanical explanation of electrons in atoms. In his [[Bohr model|model]], electrons existed in quantized orbits around the atomic nucleus. Soon after this in 1916, [[Gilbert Newton Lewis]] and [[Irving Langmuir]] explained the chemical bonding of elements by electronic interactions. In 1925 Bohr's model of the atom was superseded by the wave description of electrons involving Schrodinger's wave equation, where electrons exist in orbitals. This model is still in use today. The electronic structure of atoms is the source of structure and periodicity found in the [[periodic table]] of [[elements]].
  
 
==See also==
 
==See also==
Line 125: Line 86:
 
* [[Subatomic particle]]
 
* [[Subatomic particle]]
 
* [[Proton]]
 
* [[Proton]]
* [[Positron]]
 
 
* [[Neutron]]
 
* [[Neutron]]
 
* [[Photoelectric Effect]]
 
* [[Photoelectric Effect]]
 
* [[Lightning]]
 
* [[Lightning]]
* [[List of particles]]
 
 
* [[Cathode rays]]
 
* [[Cathode rays]]
 
* [[Electricity]]
 
* [[Electricity]]
 
* [[Fermion field]]
 
* [[Fermion field]]
 +
 +
==References ==
 +
* Brumfiel, G. “Can electrons do the splits?” ''Nature'' 433 (January 6, 2005): 11.
 +
* Griffiths, David J. ''Introduction to Quantum Mechanics'', 2nd ed. Prentice Hall, 2004. ISBN 013805326X
 +
* Tipler, Paul, and Ralph Llewellyn. ''Modern Physics'', 4th ed. W. H. Freeman, 2002. ISBN 0716743450
  
 
==External links==
 
==External links==
* [http://www.aip.org/history/electron/ The Discovery of the Electron] from the American Institute of Physics History Center
+
All links retrieved September 17, 2013.
 +
 
 +
* [http://www.aip.org/history/electron/ The Discovery of the Electron] &ndash; American Institute of Physics History Center.
 
* [http://pdg.lbl.gov/ Particle Data Group]
 
* [http://pdg.lbl.gov/ Particle Data Group]
* Stoney, G. Johnstone, "''[http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Stoney-1894.html Of the 'Electron,' or Atom of Electricity]''". Philosophical Magazine. Series 5, Volume 38, p. 418-420 October 1894.
+
* [http://scienceworld.wolfram.com/physics/Electron.html Eric Weisstein's World of Physics: Electron]
* Eric Weisstein's World of Physics: [http://scienceworld.wolfram.com/physics/Electron.html Electron]
 
  
==References ==
 
*{{Book reference | Author=Griffiths, David J.|Title=Introduction to Quantum Mechanics (2nd ed.) | Publisher=Prentice Hall |Year=2004 |ID=ISBN 013805326X}}
 
*{{Book reference | Author=Tipler, Paul; Llewellyn, Ralph | Title=Modern Physics (4th ed.) | Publisher=W. H. Freeman | Year=2002 | ID=ISBN 0716743450}}
 
* Brumfiel, G. ([[6 January]] [[2005]]). Can electrons do the splits? In ''Nature, 433'', 11.
 
  
{{Elementary}}
+
{{Natural sciences-footer}}
  
[[Category:Leptons]]
+
[[Category:Physical sciences]]
[[Category:Atomic physics]]
+
[[Category:Chemistry]]
[[Category:Molecular physics]]
+
[[Category:Physics]]
[[Category:Electricity]]
 
  
[[ar:إلكترون]]
+
{{Credit|26301032}}
[[ast:Electrón]]
 
[[bg:Електрон]]
 
[[br:Elektron]]
 
[[ca:Electró]]
 
[[cs:Elektron]]
 
[[da:Elektron]]
 
[[de:Elektron]]
 
[[et:Elektron]]
 
[[es:Electrón]]
 
[[eo:Elektrono]]
 
[[fa:الکترون]]
 
[[fr:Électron]]
 
[[ga:Leictreon]]
 
[[gl:Electrón]]
 
[[ko:전자]]
 
[[hr:Elektron]]
 
[[io:Elektrono]]
 
[[id:Elektron]]
 
[[ia:Electron]]
 
[[is:Rafeind]]
 
[[it:Elettrone]]
 
[[he:אלקטרון]]
 
[[la:Electron]]
 
[[lv:Elektrons]]
 
[[lt:Elektronas]]
 
[[hu:Elektron]]
 
[[mk:Електрон]]
 
[[nl:Elektron]]
 
[[nds:Elektron]]
 
[[ja:電子]]
 
[[no:Elektron]]
 
[[nn:Elektron]]
 
[[pl:Elektron]]
 
[[pt:Elétron]]
 
[[ro:Electron]]
 
[[ru:Электрон]]
 
[[simple:Electron]]
 
[[sl:Elektron]]
 
[[sr:Електрон]]
 
[[su:Éléktron]]
 
[[fi:Elektroni]]
 
[[sv:Elektron]]
 
[[th:อิเล็กตรอน]]
 
[[vi:Điện tử]]
 
[[zh:电子]]
 

Revision as of 13:41, 17 September 2013

Electron
The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density
Classification
Elementary particle
Fermion
Lepton
First Generation
Electron
Properties
Mass: 9.109 3826(16) × 10−31 kg
11836.152 672 61(85) amu
0.510 998 918(44) MeV/c2
Electric Charge: −1.602 176 53(14) × 10−19 C
Spin: ½
Color Charge: none
Interaction: Gravity, Electromagnetic,
Weak

The electron is a fundamental subatomic particle, which carries a negative electric charge. Electrons generate an electric field. In organized motion they constitute electric current and generate a magnetic field. Electric current over time is a form of energy (electricity) that may be harnessed as a practical means to perform work. Electrons are found within atoms and surround the nucleus of protons and neutrons in a particular electron configuration. It is the electonic configuration of atoms that determines an element’s physical and chemical properties. The exchange or sharing of electrons constitute chemical bonds, and they are thus important in demonstrating the relational nature of physical existence.

The word electron was coined in 1894 and is derived from the term “electric,” whose ultimate origin is the Greek word 'ηλεκτρον, meaning amber.

Characteristics

The electron is one of a class of subatomic particles called leptons which are believed to be fundamental particles. As an elementary particle it is not considered to have any substructure (at least, experiments have not found any so far) and there is good reason to believe that there is not any. Hence, it is usually described as point-like, i.e. with no spatial extension. However, if one gets very near an electron, one notices that its properties (charge and mass) seem to change. This is an effect common to all elementary particles: the particle influences the vacuum fluctuations in its vicinity, so that the properties one observes from far away are the sum of the bare properties and the vacuum effects (see renormalization).

The antimatter counterpart of the electron is its antiparticle, the positron.

Charged particles, monatomic ions and larger particles, arise from an imbalance in the total number of electrons and protons in the particle. When there is an excess of electrons, the object is said to be negatively charged. When there are fewer electrons than protons, the object is said to be positively charged. When the number of electrons and the number of protons are equal, the object is said to be electrically neutral. A macroscopic body can acquire charge through rubbing, i.e. the phenomena of triboelectricity.

Electrons have a negative electric charge of −1.6 × 10−19 coulombs (this is usually just stated as a charge of −1) and a mass of about 9.11 × 10−31 kilograms (0.51 MeV/c2), which is approximately 11836 of the mass of the proton. These are commonly represented as e. The electron has spin ½, which implies it is a fermion, i.e., it follows the Fermi-Dirac statistics. While most electrons are found in atoms, others move independently in matter, or together as an electron beam in a vacuum. In some superconductors, electrons move in Cooper pairs, in which their motion is coupled to nearby matter via lattice vibrations called phonons. When electrons move, free of the nuclei of atoms, and there is a net flow of charge, this flow is called electricity, or an electric current. There is also a physical constant called the classical electron radius, with a value of 2.8179 × 10−15 meters. Note that this is the radius that one could infer from its charge if the physics were only described by the classical theory of electrodynamics and there were no quantum mechanics (hence, it is an outdated concept that nevertheless sometimes still proves useful in calculations).

Electrons in theory

As applied to electrons the word "particle" is somewhat misleading. This is because electrons can also behave like a wave; that is they exhibit wave-particle duality. The wave behavior of electrons can be demonstrated in the interference patterns produced in a double-slit experiment, and is employed in the electron microscope. The wave nature of electrons is essential to the quantum mechanics of the electromagnetic interaction, where electrons are represented by wavefunctions. From the square of the wavefunction the electron density can be determined. Also, the exact momentum and position of an electron cannot be simultaneously determined. This is a limitation described by the Heisenberg uncertainty principle, which, in this instance, simply states that the more accurately we know a particle's position, the less accurately we can know its momentum and vice versa.

In relativistic quantum mechanics, the electron is described by the Dirac Equation. Quantum electrodynamics (QED) models an electron as a charged particle surrounded a sea of interacting virtual particles, modifying the sea of virtual particles which makes up a vacuum. Treating the electron as a dimensionless point, however, gives calculations that produce infinite terms. In order to remove these infinities a practical (although mathematically dubious) method called renormalization was developed whereby infinite terms can be cancelled to produce finite predictions about the electron. The correction of just over 0.1 percent to the predicted value of the electron's gyromagnetic ratio from exactly 2 (as predicted by Dirac's single particle model), and it's extraordinarily precise agreement with the experimentally determined value is viewed as one of the pinnacles of modern physics. There are now indications that string theory and its descendants may provide a model of the electron and other fundamental particles where the infinities in calculations do not appear, because the electron is no longer seen as a dimensionless point. At present, string theory is very much a 'work in progress' and lacks predictions analogous to those made by QED that can be experimentally verified.

In the Standard Model of particle physics there are three generations of matter particles. In this model the muon and the tauon correspond to the electron in the other two generations. Also in the model each fundamental particle has an antiparticle counterpart. The antiparticle of the electron is the positron (see below). Electrons are also a key element in electromagnetism, an approximate theory that is adequate for macroscopic systems, and for classical modeling of microscopic systems.

History

The electron has a special place in the history of understanding matter. It was the first subatomic particle to be discovered and was important in the development of quantum mechanics. As a unit of charge in electrochemistry it was posited by G. Johnstone Stoney in 1874. In 1894, he also invented the word itself.

The discovery that the electron was a subatomic particle was made in 1897 by J.J. Thomson at the Cavendish Laboratory at Cambridge University, while he was studying "cathode rays." Influenced by the work of James Clerk Maxwell, and the discovery of the X-ray, he deduced that cathode rays existed and were negatively charged "particles," which he called "corpuscles." He published his discovery in 1897. Thomson's work only allowed him to determine charge to mass ratio of the electron. It was Millikan's oil-drop experiment of 1909 that measured the charge on the electron and thus allowed calculation of its mass.

The first quantum mechanical theories were explanations of the electronic stucture of atoms. In 1913 Neils Bohr proposed the first quantum mechanical explanation of electrons in atoms. In his model, electrons existed in quantized orbits around the atomic nucleus. Soon after this in 1916, Gilbert Newton Lewis and Irving Langmuir explained the chemical bonding of elements by electronic interactions. In 1925 Bohr's model of the atom was superseded by the wave description of electrons involving Schrodinger's wave equation, where electrons exist in orbitals. This model is still in use today. The electronic structure of atoms is the source of structure and periodicity found in the periodic table of elements.

See also

References
ISBN links support NWE through referral fees

  • Brumfiel, G. “Can electrons do the splits?” Nature 433 (January 6, 2005): 11.
  • Griffiths, David J. Introduction to Quantum Mechanics, 2nd ed. Prentice Hall, 2004. ISBN 013805326X
  • Tipler, Paul, and Ralph Llewellyn. Modern Physics, 4th ed. W. H. Freeman, 2002. ISBN 0716743450

External links

All links retrieved September 17, 2013.


General subfields within the Natural sciences
Astronomy | Biology | Chemistry | Earth science | Ecology | Physics

Credits

New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

The history of this article since it was imported to New World Encyclopedia:

Note: Some restrictions may apply to use of individual images which are separately licensed.