A stable subatomic particle in the lepton family having a rest mass of 9.1066 × 10-28 grams and a unit negative electric charge of approximately 1.602 × 10-19 coulombs.
[ELECTR(IC) + –ON1.]
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n. (Abbr. e)
Sci-Tech Encyclopedia:
Electron
An elementary particle which is the negatively charged constituent of ordinary matter. The electron is the lightest known particle which possesses an electric charge. Its rest mass is me ≅ 9.1 × 10−28 g, about 1/1836 of the mass of the proton or neutron, which are, respectively, the positively charged and neutral constituents of ordinary matter. Discovered in 1895 by J. J. Thomson in the form of cathode rays, the electron was the first elementary particle to be identified.
The charge of the electron is −e ≅ −4.8 × 10−10 esu = −1.6 × 10−19 coulomb. The sign of the electron's charge is negative by convention, and that of the equally charged proton is positive. This is a somewhat unfortunate convention, because the flow of electrons in a conductor is thus opposite to the conventional direction of the current.
Electrons are emitted in radioactivity (as beta rays) and in many other decay processes; for instance, the ultimate decay products of all mesons are electrons, neutrinos, and photons, the meson's charge being carried away by the electrons. The electron itself is completely stable. Electrons contribute the bulk to ordinary matter; the volume of an atom is nearly all occupied by the cloud of electrons surrounding the nucleus, which occupies only about 10−13 of the atom's volume. The chemical properties of ordinary matter are determined by the electron cloud.
The electron obeys the Fermi-Dirac statistics, and for this reason is often called a fermion. One of the primary attributes of matter, impenetrability, results from the fact that the electron, being a fermion, obeys the Pauli exclusion principle; the world would be completely different if the lightest charged particle were a boson, that is, a particle that obeys Bose-Einstein statistics.
Magnetic moment
The electron has magnetic properties by virtue of (1) its orbital motion about the nucleus of its parent atom and (2) its rotation about its own axis. The magnetic properties are best described through the magnetic dipole moment associated with 1 and 2. The classical analog of the orbital magnetic dipole moment is the dipole moment of a small current-carrying circuit. The electron spin magnetic dipole moment may be thought of as arising from the circulation of charge, that is, a current, about the electron axis; but a classical analog to this moment has much less meaning than that to the orbital magnetic dipole moment. The magnetic moments of the electrons in the atoms that make up a solid give rise to the bulk magnetism of the solid.
Spin
That property of an electron which gives rise to its angular momentum about an axis within the electron. Spin is one of the permanent and basic properties of the electron. Both the spin and the associated magnetic dipole moment of the electron were postulated by G. E. Uhlenbeck and S. Goudsmit in 1925 as necessary to allow the interpretation of many observed effects, among them the so-called anomalous Zeeman effect, the existence of doublets (pairs of closely spaced lines) in the spectra of the alkali atoms, and certain features of x-ray spectra.
The spin quantum number is s, where s is always ½. This means that the component of spin angular momentum along a preferred direction, such as the direction of a magnetic field, is ± ½ℏ, where ℏ is Planck's constant h divided by 2π. The spin angular momentum of the electron is not to be confused with the orbital angular momentum of the electron associated with its motion about the nucleus. In the latter case the maximum component of angular momentum along a preferred direction is lℏ, where l is the angular momentum quantum number and may be any positive integer or zero.
The electron has a magnetic dipole moment by virtue of its spin. The approximate value of the dipole moment is the Bohr magneton μ0 which is equal to eh/4πmc = 9.27 × 10−21 erg/oersted, where e is the electron charge measured in electrostatic units, m is the mass of the electron, and c is the velocity of light. (In SI units, μ0 = 9.27 × 10−24 joule/tesla.) The orbital motion of the electron also gives rise to a magnetic dipole moment μl, that is equal to μ0 when l = 1.
Computer Desktop Encyclopedia:
electron
An elementary particle that circles the nucleus of an atom. Electrons are considered to be negatively charged. See wave-particle duality and photon.
Dental Dictionary:
electron (e)
(ē-lek′tron)
n
A negatively charged elementary particle constituent in every neutral atom, with a mass of 0.000549. (Particles with an equal but opposite charge are called positrons.)
Measures and Units:
electron
sub-atomic physics Values
[Mohr P. J., Taylor B. N. CODATA Recommended Values of the Fundamental Physical Constants: 2002 (to be published)]
[Mohr P. J., Taylor B. N. Rev. Mod. Phys. Vol. 72:351-495 (2000)]
[Mohr P. Phys. Today Vol. 53:7, 11-16 (2000)]
[For latest recommended values, see
| electron charge | 1.602 176 53(14) × 10-19 C | 8.5 × 10-8 |
| = -1.0 × elementary charge, | ||
| electron gyromagnetic ratio (γe) | 1.760 859 74(15) | |
| × 1011 s-1·T-1 | 8.6 × 10-8 | |
| electron magnetic moment (μe) | -9.284 764 12(80) | |
| × 10-24 J·T-1 | 8.6 × 10-8 | |
| electron mass (me) | 9.109 382 6(16) × 10-31 kg | 1.7 × 10-7 |
| classical electron radius | 2.817 940 325(28) × 10-15·m | 1.0 × 10-8 |
For relative masses, see neutron; proton.
Britannica Concise Encyclopedia:
electron
For more information on electron, visit Britannica.com.
Columbia Encyclopedia:
electron,
elementary particle carrying a unit charge of negative electricity. Ordinary electric current is the flow of electrons through a wire conductor (see electricity). The electron is one of the basic constituents of matter. An atom consists of a small, dense, positively charged nucleus surrounded by electrons that whirl about it in orbits, forming a cloud of charge. Ordinarily there are just enough negative electrons to balance the positive charge of the nucleus, and the atom is neutral. If electrons are added or removed, a net charge results, and the atom is said to be ionized (see ion). Atomic electrons are responsible for the chemical properties of matter (see valence). The name electron was first used for a unit of negative electricity by the English physicist G. J. Stoney in the late 19th cent. The actual discovery of the particle, however, was made in 1897 by J. J. Thomson, who showed that cathode rays are composed of electrons and who measured the ratio of charge to mass for the electron. In 1909, R. A. Millikan measured the charge of the electron. Combining these two results gives the mass of the electron (about 1/1,840 of the mass of the proton). Ernest Rutherford, in 1903, showed that beta rays (see radioactivity) are high-energy electrons. In 1927, Davisson and Germer, working with high-speed electron beams, discovered that electrons sometimes exhibit the wave property of diffraction. This confirmed L. V. de Broglie's hypothesis that electrons, which had previously been thought of as particles, also possess certain wave properties (see quantum theory). The wavelike properties of electrons are utilized in the electron microscope and other devices. The electron is the lightest particle having a non-zero rest mass. It belongs to the lepton class of particles and, together with its antiparticle, the positron, and its associated neutrino and antineutrino, constitutes a subfamily of the leptons. In any particle reaction involving any of the four members of the electron family, the total electron family number (+1 for ordinary particles, −1 for antiparticles) must be conserved (see conservation laws, in physics). As a consequence, an electron and a positron (total electron family number equals zero) can annihilate each other to yield two or more photons or a neutrino-antineutrino pair, but not two neutrinos (total electron family number equals two).
Science Dictionary:
electron
(i-lek-tron)
An elementary particle with a negative charge and a very small mass. Electrons are normally found in orbits around the nucleus of an atom. The chemical reactions that an atom undergoes depend primarily on the electrons in the outermost orbits (the valence electrons).
Veterinary Dictionary:
electron
Any of the negatively charged particles arranged in orbits around the nucleus of an atom and determining all of the atom's physical and chemical properties except mass and radioactivity. Electrons flowing in a conductor constitute an electric current; when ejected from a radioactive substance, they constitute the beta particles.
- e. acceptor — see oxidant.
- e. beam — the stream of electrons that flows from the anode to the cathode in the x-ray tube and then interacts with the tungsten target to produce x-rays.
- e. carrier — a molecule associated with membrane-bound proteins that accepts and transfers electrons.
- e. donor — see reductant.
- e. micrographs — photographic images of electron microscopic fields.
- e. microscope — see electron microscope.
- e. microscopy — technology of using an electron microscope.
Word Tutor:
electron
IN BRIEF: A very tiny particle that has a negative charge and moves around the nucleus of an atom.
The negative electrical charge put off by an electron allows it to move in a circle around the nucleus of an atom.
Wikipedia:
electron
"e-" redirects here. For the Internet-related prefix e-,
see Wiktionary's entry e-.
| Electron | |
 Theoretical estimates of the electron density for the first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density |
|
| Composition: | Elementary particle |
|---|---|
| Family: | Fermion |
| Group: | Lepton |
| Generation: | First |
| Interaction: | |
| Antiparticle: | Positron |
| Theorized: | G. Johnstone Stoney (1874) |
| Discovered: | J.J. Thomson (1897) |
| Symbol: | e−, β− |
| Mass: | 9.109 382 15(45) × 10–31 kg[1] 5.485 799 09(27) × 10–4 u 1⁄1822.888 4843(11) u |
| Electric charge: | –1.602 176 487(40) × 10–19 C[2] |
| Spin: | ½ |
The electron is a fundamental
History
The name electron comes from the Greek word for amber, ήλεκτρον. This material played an essential role in the discovery of electrical phenomena. The ancient Greeks knew, for example, that rubbing a piece of amber with fur left an electric charge on its surface, which could then create sparks. For more about the history of the term electricity, see History of electricity.
The electron as a unit of charge in electrochemistry was posited by G. Johnstone Stoney in 1874, who also coined the term electron in 1894.
In this paper an estimate was made of the actual amount of this most remarkable fundamental unit of electricity, for which I have since ventured to suggest the name electron.
—Stoney, George Johnstone (October 1894). "Of the "Electron," or Atom of Electricity". Philosophical Magazine 38 (5): 418-420.
During the late 1890s a number of physicists posited that electricity could be conceived of as being made of discrete units, which were given a variety of names, but their reality had not been confirmed in a compelling way.
The discovery that the electron was a
The electron's charge was carefully measured by R. A. Millikan in his oil-drop experiment of 1909.
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 element. 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 in terms of 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 explained the chemical bonding of elements by electronic interactions.
Classification
The electron is in the class of subatomic particles called leptons, which are believed to be fundamental particles.
As with all particles, electrons can also act as waves. This is called the wave-particle duality, also known by the term complementarity coined by Niels Bohr, can be demonstrated using the double-slit experiment.
The antiparticle of an electron is the positron, which has the same mass but positive rather than negative charge. The discoverer of the positron, Carl D. Anderson, proposed calling standard electrons negatrons, and using electron as a generic term to describe both the positively and negatively charged variants. This usage never caught on and is rarely, if ever, encountered today.
Properties and behavior
Electrons have an electric charge of −1.6022 × 10−19 coulomb, a mass of 9.11 × 10−31 kg based on charge/mass measurements and a relativistic rest mass of about 0.511 MeV/c². The mass of the electron is approximately 1/1836 of the mass of the proton. The common electron symbol is e−.[1]
According to quantum mechanics, electrons can be represented by wavefunctions, from which a calculated probabilistic electron density can be determined. The orbital of each electron in an atom can be described by a wavefunction. Based on the Heisenberg uncertainty principle, the exact momentum and position of the actual electron cannot be simultaneously determined. This is a limitation 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 ½ and is a fermion (it follows Fermi-Dirac statistics). In addition to its intrinsic angular momentum, an electron has an intrinsic magnetic moment along its spin axis.
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. When free electrons move, there is a net flow of charge, this flow is called an electric current. The drift velocity of electrons in metal wires is on the order of mm/hour. However, the speed at which a current at one point in a wire causes a current in other parts of the wire is typically 75% of light speed.
In some superconductors, pairs of electrons move as Cooper pairs in which their motion is coupled to nearby matter via lattice vibrations called phonons. The distance of separation between Cooper pairs is roughly 100 nm. (Rohlf, J.W.)
A body has an electric charge when that body 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 protons, the object is said to be positively charged. When the number of electrons and the number of protons are equal, their charges cancel each other and the object is said to be electrically neutral. A macroscopic body can develop an electric charge through rubbing, by the phenomenon of triboelectricity.
When electrons and positrons collide, they annihilate each other and produce pairs of high energy photons or other particles. On the other hand, high-energy photons may transform into an electron and a positron by a process called pair production, but only in the presence of a nearby charged particle, such as a nucleus.
The electron is currently described as a fundamental particle or an elementary particle. It has no substructure. Hence, for convenience, it is usually defined or assumed to be a point-like mathematical point charge, with no spatial extension. However, when a test particle is forced to approach an electron, we measure changes in its properties (charge and mass). This effect is common to all elementary particles: Current theory suggests that this effect is due to the influence of vacuum fluctuations in its local space, so that the properties measured from a significant distance are considered to be the sum of the bare properties and the vacuum effects (see renormalization).
The classical electron radius is 2.8179 × 10−15 m. This is the radius that is inferred from the electron's electric charge, by using the classical theory of electrodynamics alone, ignoring quantum mechanics. Classical electrodynamics (Maxwell's electrodynamics) is the older concept that is widely used for practical applications of electricity, electrical engineering, semiconductor physics, and electromagnetics; quantum electrodynamics, on the other hand, is useful for applications involving modern particle physics and some aspects of optical, laser and quantum physics.
Based on current theory, the speed of an electron can approach, but never reach, c (the speed of light in a vacuum). This limitation is attributed to Einstein's theory of special relativity which defines the speed of light as a constant within all inertial frames. However, when relativistic electrons are injected into a dielectric medium, such as water, where the local speed of light is significantly less than c, the electrons will (temporarily) be traveling faster than light in the medium. As they interact with the medium, they generate a faint bluish light, called Cherenkov radiation.
The effects of special relativity are based on a quantity known as γ or the Lorentz factor. γ is a function of v, the velocity of the particle. It is defined as:
The energy necessary to accelerate a particle is:
For example, the Stanford linear accelerator can accelerate an electron to roughly 51 GeV [1]. This gives a gamma of 100,000, since the rest mass of an electron is 0.51 MeV/c² (the relativistic mass of this electron is 100,000 times its rest mass). Solving the equation above for the speed of the electron (and using an approximation for large γ) gives:
In practice
In the universe
Scientists believe that the number of electrons existing in the known universe is at least 1079. This number amounts to an average density of about one electron per cubic metre of space. Astronomers have estimated that 90% of the mass of atoms in the universe is hydrogen, which is made of one electron and one proton.
In industry
Electron beams are used in welding, lithography, scanning electron microscopes and transmission electron microscopes. LEED and RHEED are also important tools where electrons are used.
They are also at the heart of cathode ray tubes, which are used extensively as display devices in laboratory instruments, computer monitors and television sets. In photomultiplier tubes, one photon strikes the photocathode, initiating an avalanche of electrons that produces a detectable current.
In the laboratory
Electron microscopes 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.
In medicine
In radiation therapy, electron beams are used for treatment of superficial tumours.
In theory
In relativistic quantum mechanics, the electron is described by the Dirac Equation which defines the electron as a (mathematical) point. In quantum field theory, the reaction of the electron is described by quantum electrodynamics (QED), a U(1) gauge theory. In Dirac's model, an electron is defined to be a mathematical point, a point-like, charged "bare" particle surrounded by a sea of interacting pairs of virtual particles and antiparticles. These provide a correction of just over 0.1% to the predicted value of the electron's gyromagnetic ratio from exactly 2 (as predicted by Dirac's single-particle model). The extraordinarily precise agreement of this prediction with the experimentally determined value is viewed as one of the great achievements of modern physics.[3]
In the Standard Model of particle physics, the electron is the first-generation charged lepton. It forms a weak isospin doublet with the electron neutrino; these two particles interact with each other through both the charged and neutral current weak interaction. The electron is very similar to the two more massive particles of higher generations, the muon and the tau lepton, which are identical in charge, spin, and interaction but differ in mass.
The antimatter counterpart of the electron is 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 annihilate each other, giving rise to two gamma-ray photons emitted at roughly 180° to each other. If the electron and positron had negligible momentum, each gamma ray will have an energy of 0.511 MeV. See also Electron-positron annihilation.
Electrons are a key element in electromagnetism, a theory that is accurate for macroscopic systems, and for classical modelling of microscopic systems.
Notes
- ^ a b All masses are 2006 CODATA values accessed via the NIST’s electron mass page. The fractional version’s denominator is the inverse of the decimal value (along with its relative standard uncertainty of 5.0 × 10–8)
- ^ The electron’s charge is the negative of elementary charge (which is a positive value for the proton). CODATA value accessed via the NIST’s elementary charge page.
- ^ *Griffiths, David J. (2004). Introduction to Quantum Mechanics (2nd ed.). Prentice Hall. ISBN 0-13-805326-X.
See also
External links
- The NIST’s latest CODATA value for electron mass
- The Discovery of the Electron from the American Institute of Physics History Center
- Particle Data Group
- Stoney, G. Johnstone, "Of the 'Electron,' or Atom of Electricity". Philosophical Magazine. Series 5, Volume 38, p. 418-420 October 1894.
- Eric Weisstein's World of Physics: Electron
- Researchers Catch Motion of a Single Electron on Video
| Particles in physics | |
|---|---|
| Elementary particles | Fermions:
Quarks: u · d ·
s · c · b ·
t • Leptons: e- · e+ · μ- ·
μ+ · τ- · τ+ · νe · νμ · ντ Bosons: Gauge bosons: γ · g · W± · Z0 Other: Ghosts |
| Composite particles | Hadrons: Baryons(list)/Hyperons/Nucleons:
p · n · Δ ·
Λ · Σ · Ξ
· Ω · Ξb • Mesons(list)/Quarkonia:
π · K · ρ · J/ψ · Υ Other: Atomic nuclei • Atoms • Exotic atoms: Positronium • Molecules |
| Hypothetical elementary particles | Superpartners: Axino · Dilatino ·
Chargino · Gluino · Gravitino · Higgsino · Neutralino ·
Sfermion · Slepton · Squark Other: Axion · Dilaton · Goldstone boson · Graviton · Higgs boson · Tachyon · X · Y · W' · Z' |
| Hypothetical composite particles | Exotic
hadrons: Exotic baryons: Other: Mesonic molecule |
| Quasiparticles | Davydov soliton · Exciton · Magnon · Phonon · Plasmon · Polariton · Polaron |
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Translations:
Electron
idioms:
- electron gun elektronkanon
- electron microscope elektronmikroskop
Nederlands (Dutch)
elektron (elementair deeltje van atoom)
Français (French)
n. - électron
idioms:
- electron gun canon à électrons
- electron microscope microscope à électrons
Deutsch (German)
n. - Elektron
idioms:
- electron gun Elektronenkanone, Elektronenstrahlsystem
- electron microscope Elektronenmikroskop
Ελληνική (Greek)
n. - (φυσ.) ηλεκτρόνιο
idioms:
- electron gun πυροβόλο ηλεκτρονίων
- electron microscope (τεχνολ.) ηλεκτρονικό μικροσκόπιο
idioms:
- electron microscope microscopio elettronico
Português (Portuguese)
n. - elétron (Quím.) (Fís.) (m)
idioms:
- electron microscope microscópio (m) eletrônico
idioms:
- electron microscope электронный микроскоп
Español (Spanish)
n. - electrón
idioms:
- electron gun arma electrónica
- electron microscope microscopio electrónico
Svenska (Swedish)
n. - elektron
中文（简体） (Chinese (Simplified))
电子
idioms:
- electron gun 电子枪
- electron microscope 电子显微镜
中文（繁體） (Chinese (Traditional))
n. - 電子
idioms:
- electron gun 電子槍
- electron microscope 電子顯微鏡
日本語 (Japanese)
n. - 電子, エレクトロン
idioms:
- electron microscope 電子顕微鏡
العربيه (Arabic)
(الاسم) الألكترون
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