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In , German physicist Hermann von Helmholtz argued that both positive and negative charges were divided into elementary parts, each of which "behaves like atoms of electricity".
Stoney initially coined the term electrolion in Ten years later, he switched to electron to describe these elementary charges, writing in " A proposal to change to electrion failed because Hendrik Lorentz preferred to keep electron.
The discovery of electrons by Joseph Thomson was closely tied with the experimental and theoretical research of cathode rays for decades by many physicists.
In , Plucker's student Johann Wilhelm Hittorf found that a solid body placed in between the cathode and the phosphorescence would cast a shadow upon the phosphorescent region of the tube.
Hittorf inferred that there are straight rays emitted from the cathode and that the phosphorescence was caused by the rays striking the tube walls.
In , the German physicist Eugen Goldstein showed that the rays were emitted perpendicular to the cathode surface, which distinguished between the rays that were emitted from the cathode and the incandescent light.
Goldstein dubbed the rays cathode rays. During the s, the English chemist and physicist Sir William Crookes developed the first cathode ray tube to have a high vacuum inside.
Therefore, he concluded that the rays carried momentum. Furthermore, by applying a magnetic field, he was able to deflect the rays, thereby demonstrating that the beam behaved as though it were negatively charged.
The German-born British physicist Arthur Schuster expanded upon Crookes' experiments by placing metal plates parallel to the cathode rays and applying an electric potential between the plates.
The field deflected the rays toward the positively charged plate, providing further evidence that the rays carried negative charge. By measuring the amount of deflection for a given level of current , in Schuster was able to estimate the charge-to-mass ratio [c] of the ray components.
However, this produced a value that was more than a thousand times greater than what was expected, so little credence was given to his calculations at the time.
In Hendrik Lorentz suggested that the mass of these particles electrons could be a consequence of their electric charge.
While studying naturally fluorescing minerals in , the French physicist Henri Becquerel discovered that they emitted radiation without any exposure to an external energy source.
These radioactive materials became the subject of much interest by scientists, including the New Zealand physicist Ernest Rutherford who discovered they emitted particles.
He designated these particles alpha and beta , on the basis of their ability to penetrate matter. In , the British physicist J. Thomson , with his colleagues John S.
Townsend and H. Wilson , performed experiments indicating that cathode rays really were unique particles, rather than waves, atoms or molecules as was believed earlier.
He further showed that the negatively charged particles produced by radioactive materials, by heated materials and by illuminated materials were universal.
Fitzgerald, J. Larmor, and H. The electron's charge was more carefully measured by the American physicists Robert Millikan and Harvey Fletcher in their oil-drop experiment of , the results of which were published in This experiment used an electric field to prevent a charged droplet of oil from falling as a result of gravity.
This device could measure the electric charge from as few as 1— ions with an error margin of less than 0.
Comparable experiments had been done earlier by Thomson's team,  using clouds of charged water droplets generated by electrolysis, and in by Abram Ioffe , who independently obtained the same result as Millikan using charged microparticles of metals, then published his results in Around the beginning of the twentieth century, it was found that under certain conditions a fast-moving charged particle caused a condensation of supersaturated water vapor along its path.
In , Charles Wilson used this principle to devise his cloud chamber so he could photograph the tracks of charged particles, such as fast-moving electrons.
By , experiments by physicists Ernest Rutherford , Henry Moseley , James Franck and Gustav Hertz had largely established the structure of an atom as a dense nucleus of positive charge surrounded by lower-mass electrons.
The electrons could move between those states, or orbits, by the emission or absorption of photons of specific frequencies. By means of these quantized orbits, he accurately explained the spectral lines of the hydrogen atom.
Chemical bonds between atoms were explained by Gilbert Newton Lewis , who in proposed that a covalent bond between two atoms is maintained by a pair of electrons shared between them.
With this model Langmuir was able to qualitatively explain the chemical properties of all elements in the periodic table,  which were known to largely repeat themselves according to the periodic law.
In , Austrian physicist Wolfgang Pauli observed that the shell-like structure of the atom could be explained by a set of four parameters that defined every quantum energy state, as long as each state was occupied by no more than a single electron.
This prohibition against more than one electron occupying the same quantum energy state became known as the Pauli exclusion principle.
In , they suggested that an electron, in addition to the angular momentum of its orbit, possesses an intrinsic angular momentum and magnetic dipole moment.
The intrinsic angular momentum became known as spin , and explained the previously mysterious splitting of spectral lines observed with a high-resolution spectrograph ; this phenomenon is known as fine structure splitting.
The corpuscular properties of a particle are demonstrated when it is shown to have a localized position in space along its trajectory at any given moment.
In , George Paget Thomson discovered the interference effect was produced when a beam of electrons was passed through thin metal foils and by American physicists Clinton Davisson and Lester Germer by the reflection of electrons from a crystal of nickel.
De Broglie's prediction of a wave nature for electrons led Erwin Schrödinger to postulate a wave equation for electrons moving under the influence of the nucleus in the atom.
In , this equation, the Schrödinger equation , successfully described how electron waves propagated. This approach led to a second formulation of quantum mechanics the first by Heisenberg in , and solutions of Schrödinger's equation, like Heisenberg's, provided derivations of the energy states of an electron in a hydrogen atom that were equivalent to those that had been derived first by Bohr in , and that were known to reproduce the hydrogen spectrum.
This led him to predict the existence of a positron, the antimatter counterpart of the electron. In , Willis Lamb , working in collaboration with graduate student Robert Retherford , found that certain quantum states of the hydrogen atom, which should have the same energy, were shifted in relation to each other; the difference came to be called the Lamb shift.
About the same time, Polykarp Kusch , working with Henry M. Foley , discovered the magnetic moment of the electron is slightly larger than predicted by Dirac's theory.
This small difference was later called anomalous magnetic dipole moment of the electron. This difference was later explained by the theory of quantum electrodynamics , developed by Sin-Itiro Tomonaga , Julian Schwinger and Richard Feynman in the late s.
With the development of the particle accelerator during the first half of the twentieth century, physicists began to delve deeper into the properties of subatomic particles.
His initial betatron reached energies of 2. This radiation was caused by the acceleration of electrons through a magnetic field as they moved near the speed of light.
With a beam energy of 1. In the Standard Model of particle physics, electrons belong to the group of subatomic particles called leptons , which are believed to be fundamental or elementary particles.
Electrons have the lowest mass of any charged lepton or electrically charged particle of any type and belong to the first- generation of fundamental particles.
Leptons differ from the other basic constituent of matter, the quarks , by their lack of strong interaction. The invariant mass of an electron is approximately 9.
On the basis of Einstein 's principle of mass—energy equivalence , this mass corresponds to a rest energy of 0. The ratio between the mass of a proton and that of an electron is about Within the limits of experimental accuracy, the electron charge is identical to the charge of a proton, but with the opposite sign.
In addition to spin, the electron has an intrinsic magnetic moment along its spin axis. The electron has no known substructure. The issue of the radius of the electron is a challenging problem of modern theoretical physics.
The admission of the hypothesis of a finite radius of the electron is incompatible to the premises of the theory of relativity.
On the other hand, a point-like electron zero radius generates serious mathematical difficulties due to the self-energy of the electron tending to infinity.
There is also a physical constant called the " classical electron radius ", with the much larger value of 2.
However, the terminology comes from a simplistic calculation that ignores the effects of quantum mechanics ; in reality, the so-called classical electron radius has little to do with the true fundamental structure of the electron.
There are elementary particles that spontaneously decay into less massive particles. An example is the muon , with a mean lifetime of 2. The electron, on the other hand, is thought to be stable on theoretical grounds: the electron is the least massive particle with non-zero electric charge, so its decay would violate charge conservation.
As with all particles, electrons can act as waves. This is called the wave—particle duality and can be demonstrated using the double-slit experiment.
The wave-like nature of the electron allows it to pass through two parallel slits simultaneously, rather than just one slit as would be the case for a classical particle.
When the absolute value of this function is squared , it gives the probability that a particle will be observed near a location—a probability density.
Electrons are identical particles because they cannot be distinguished from each other by their intrinsic physical properties. In quantum mechanics, this means that a pair of interacting electrons must be able to swap positions without an observable change to the state of the system.
Since the absolute value is not changed by a sign swap, this corresponds to equal probabilities. Bosons , such as the photon, have symmetric wave functions instead.
In the case of antisymmetry, solutions of the wave equation for interacting electrons result in a zero probability that each pair will occupy the same location or state.
This is responsible for the Pauli exclusion principle , which precludes any two electrons from occupying the same quantum state.
This principle explains many of the properties of electrons. For example, it causes groups of bound electrons to occupy different orbitals in an atom, rather than all overlapping each other in the same orbit.
In a simplified picture, which often tends to give the wrong idea but may serve to illustrate some aspects, every photon spends some time as a combination of a virtual electron plus its antiparticle, the virtual positron, which rapidly annihilate each other shortly thereafter.
While an electron—positron virtual pair is in existence, the Coulomb force from the ambient electric field surrounding an electron causes a created positron to be attracted to the original electron, while a created electron experiences a repulsion.
This causes what is called vacuum polarization. In effect, the vacuum behaves like a medium having a dielectric permittivity more than unity.
Thus the effective charge of an electron is actually smaller than its true value, and the charge decreases with increasing distance from the electron.
The interaction with virtual particles also explains the small about 0. The apparent paradox in classical physics of a point particle electron having intrinsic angular momentum and magnetic moment can be explained by the formation of virtual photons in the electric field generated by the electron.
These photons cause the electron to shift about in a jittery fashion known as zitterbewegung ,  which results in a net circular motion with precession.
This motion produces both the spin and the magnetic moment of the electron. This wavelength explains the "static" of virtual particles around elementary particles at a close distance.
An electron generates an electric field that exerts an attractive force on a particle with a positive charge, such as the proton, and a repulsive force on a particle with a negative charge.
The strength of this force in nonrelativistic approximation is determined by Coulomb's inverse square law. This property of induction supplies the magnetic field that drives an electric motor.
When an electron is moving through a magnetic field, it is subject to the Lorentz force that acts perpendicularly to the plane defined by the magnetic field and the electron velocity.
This centripetal force causes the electron to follow a helical trajectory through the field at a radius called the gyroradius.
The acceleration from this curving motion induces the electron to radiate energy in the form of synchrotron radiation. This force is caused by a back-reaction of the electron's own field upon itself.
Photons mediate electromagnetic interactions between particles in quantum electrodynamics. An isolated electron at a constant velocity cannot emit or absorb a real photon; doing so would violate conservation of energy and momentum.
Instead, virtual photons can transfer momentum between two charged particles. This exchange of virtual photons, for example, generates the Coulomb force.
The acceleration of the electron results in the emission of Bremsstrahlung radiation. An inelastic collision between a photon light and a solitary free electron is called Compton scattering.
This collision results in a transfer of momentum and energy between the particles, which modifies the wavelength of the photon by an amount called the Compton shift.
Such interaction between the light and free electrons is called Thomson scattering or linear Thomson scattering. The relative strength of the electromagnetic interaction between two charged particles, such as an electron and a proton, is given by the fine-structure constant.
This value is a dimensionless quantity formed by the ratio of two energies: the electrostatic energy of attraction or repulsion at a separation of one Compton wavelength, and the rest energy of the charge.
When electrons and positrons collide, they annihilate each other, giving rise to two or more gamma ray photons. If the electron and positron have negligible momentum, a positronium atom can form before annihilation results in two or three gamma ray photons totalling 1.
In the theory of electroweak interaction , the left-handed component of electron's wavefunction forms a weak isospin doublet with the electron neutrino.
This means that during weak interactions , electron neutrinos behave like electrons. Either member of this doublet can undergo a charged current interaction by emitting or absorbing a W and be converted into the other member.
Charged current interactions are responsible for the phenomenon of beta decay in a radioactive atom.
Both the electron and electron neutrino can undergo a neutral current interaction via a Z 0 exchange, and this is responsible for neutrino-electron elastic scattering.
An electron can be bound to the nucleus of an atom by the attractive Coulomb force. A system of one or more electrons bound to a nucleus is called an atom.
If the number of electrons is different from the nucleus' electrical charge, such an atom is called an ion. The wave-like behavior of a bound electron is described by a function called an atomic orbital.
Each orbital has its own set of quantum numbers such as energy, angular momentum and projection of angular momentum, and only a discrete set of these orbitals exist around the nucleus.
According to the Pauli exclusion principle each orbital can be occupied by up to two electrons, which must differ in their spin quantum number.
Electrons can transfer between different orbitals by the emission or absorption of photons with an energy that matches the difference in potential. This occurs, for example, with the photoelectric effect , where an incident photon exceeding the atom's ionization energy is absorbed by the electron.
The orbital angular momentum of electrons is quantized. Because the electron is charged, it produces an orbital magnetic moment that is proportional to the angular momentum.
The net magnetic moment of an atom is equal to the vector sum of orbital and spin magnetic moments of all electrons and the nucleus.
The magnetic moment of the nucleus is negligible compared with that of the electrons. The magnetic moments of the electrons that occupy the same orbital so called, paired electrons cancel each other out.
The chemical bond between atoms occurs as a result of electromagnetic interactions, as described by the laws of quantum mechanics.
These are electrons with opposed spins, allowing them to occupy the same molecular orbital without violating the Pauli exclusion principle much like in atoms.
Different molecular orbitals have different spatial distribution of the electron density. For instance, in bonded pairs i.
By contrast, in non-bonded pairs electrons are distributed in a large volume around nuclei. If a body has more or fewer electrons than are required to balance the positive charge of the nuclei, then that object has a net electric charge.
When there is an excess of electrons, the object is said to be negatively charged. When there are fewer electrons than the number of protons in nuclei, 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 triboelectric effect. Independent electrons moving in vacuum are termed free electrons.
Electrons in metals also behave as if they were free. In reality the particles that are commonly termed electrons in metals and other solids are quasi-electrons— quasiparticles , which have the same electrical charge, spin, and magnetic moment as real electrons but might have a different mass.
Likewise a current can be created by a changing magnetic field. These interactions are described mathematically by Maxwell's equations.
At a given temperature, each material has an electrical conductivity that determines the value of electric current when an electric potential is applied.
Examples of good conductors include metals such as copper and gold, whereas glass and Teflon are poor conductors.
In any dielectric material, the electrons remain bound to their respective atoms and the material behaves as an insulator.
Most semiconductors have a variable level of conductivity that lies between the extremes of conduction and insulation. The presence of such bands allows electrons in metals to behave as if they were free or delocalized electrons.
These electrons are not associated with specific atoms, so when an electric field is applied, they are free to move like a gas called Fermi gas  through the material much like free electrons.
Because of collisions between electrons and atoms, the drift velocity of electrons in a conductor is on the order of millimeters per second.
Metals make relatively good conductors of heat, primarily because the delocalized electrons are free to transport thermal energy between atoms.
However, unlike electrical conductivity, the thermal conductivity of a metal is nearly independent of temperature.
This is expressed mathematically by the Wiedemann—Franz law ,  which states that the ratio of thermal conductivity to the electrical conductivity is proportional to the temperature.
The thermal disorder in the metallic lattice increases the electrical resistivity of the material, producing a temperature dependence for electric current.
When cooled below a point called the critical temperature , materials can undergo a phase transition in which they lose all resistivity to electric current, in a process known as superconductivity.
In BCS theory , pairs of electrons called Cooper pairs have their motion coupled to nearby matter via lattice vibrations called phonons , thereby avoiding the collisions with atoms that normally create electrical resistance.
Electrons inside conducting solids, which are quasi-particles themselves, when tightly confined at temperatures close to absolute zero , behave as though they had split into three other quasiparticles : spinons , orbitons and holons.
According to Einstein's theory of special relativity , as an electron's speed approaches the speed of light , from an observer's point of view its relativistic mass increases, thereby making it more and more difficult to accelerate it from within the observer's frame of reference.
The speed of an electron can approach, but never reach, the speed of light in a vacuum, c. However, when relativistic electrons—that is, electrons moving at a speed close to c —are injected into a dielectric medium such as water, where the local speed of light is significantly less than c , the electrons temporarily travel faster than light in the medium.
As they interact with the medium, they generate a faint light called Cherenkov radiation. The kinetic energy K e of an electron moving with velocity v is:.
The Big Bang theory is the most widely accepted scientific theory to explain the early stages in the evolution of the Universe.
These photons were sufficiently energetic that they could react with each other to form pairs of electrons and positrons. Likewise, positron-electron pairs annihilated each other and emitted energetic photons:.
An equilibrium between electrons, positrons and photons was maintained during this phase of the evolution of the Universe. After 15 seconds had passed, however, the temperature of the universe dropped below the threshold where electron-positron formation could occur.
Most of the surviving electrons and positrons annihilated each other, releasing gamma radiation that briefly reheated the universe.
For reasons that remain uncertain, during the annihilation process there was an excess in the number of particles over antiparticles. Hence, about one electron for every billion electron-positron pairs survived.
This excess matched the excess of protons over antiprotons, in a condition known as baryon asymmetry , resulting in a net charge of zero for the universe.
This process peaked after about five minutes. Roughly one million years after the big bang, the first generation of stars began to form. These antimatter particles immediately annihilate with electrons, releasing gamma rays.
The net result is a steady reduction in the number of electrons, and a matching increase in the number of neutrons. However, the process of stellar evolution can result in the synthesis of radioactive isotopes.
Selected isotopes can subsequently undergo negative beta decay, emitting an electron and antineutrino from the nucleus.
At the end of its lifetime, a star with more than about 20 solar masses can undergo gravitational collapse to form a black hole.
However, quantum mechanical effects are believed to potentially allow the emission of Hawking radiation at this distance. Electrons and positrons are thought to be created at the event horizon of these stellar remnants.
When a pair of virtual particles such as an electron and positron is created in the vicinity of the event horizon, random spatial positioning might result in one of them to appear on the exterior; this process is called quantum tunnelling.
The gravitational potential of the black hole can then supply the energy that transforms this virtual particle into a real particle, allowing it to radiate away into space.
The rate of Hawking radiation increases with decreasing mass, eventually causing the black hole to evaporate away until, finally, it explodes.
Cosmic rays are particles traveling through space with high energies. Energy events as high as 3. The particle called a muon is a lepton produced in the upper atmosphere by the decay of a pion.
A muon, in turn, can decay to form an electron or positron. Remote observation of electrons requires detection of their radiated energy.
For example, in high-energy environments such as the corona of a star, free electrons form a plasma that radiates energy due to Bremsstrahlung radiation.
Electron gas can undergo plasma oscillation , which is waves caused by synchronized variations in electron density, and these produce energy emissions that can be detected by using radio telescopes.
The frequency of a photon is proportional to its energy. As a bound electron transitions between different energy levels of an atom, it absorbs or emits photons at characteristic frequencies.
For instance, when atoms are irradiated by a source with a broad spectrum, distinct dark lines appear in the spectrum of transmitted radiation in places where the corresponding frequency is absorbed by the atom's electrons.
Each element or molecule displays a characteristic set of spectral lines, such as the hydrogen spectral series. When detected, spectroscopic measurements of the strength and width of these lines allow the composition and physical properties of a substance to be determined.
In laboratory conditions, the interactions of individual electrons can be observed by means of particle detectors , which allow measurement of specific properties such as energy, spin and charge.
This enables precise measurements of the particle properties. For example, in one instance a Penning trap was used to contain a single electron for a period of 10 months.
The first video images of an electron's energy distribution were captured by a team at Lund University in Sweden, February The scientists used extremely short flashes of light, called attosecond pulses, which allowed an electron's motion to be observed for the first time.
The distribution of the electrons in solid materials can be visualized by angle-resolved photoemission spectroscopy ARPES. This technique employs the photoelectric effect to measure the reciprocal space —a mathematical representation of periodic structures that is used to infer the original structure.
ARPES can be used to determine the direction, speed and scattering of electrons within the material. Electron beams are used in welding.
This welding technique must be performed in a vacuum to prevent the electrons from interacting with the gas before reaching their target, and it can be used to join conductive materials that would otherwise be considered unsuitable for welding.
Electron-beam lithography EBL is a method of etching semiconductors at resolutions smaller than a micrometer. For this reason, EBL is primarily used for the production of small numbers of specialized integrated circuits.
Electron beam processing is used to irradiate materials in order to change their physical properties or sterilize medical and food products.
Linear particle accelerators generate electron beams for treatment of superficial tumors in radiation therapy. An electron beam can be used to supplement the treatment of areas that have been irradiated by X-rays.
Particle accelerators use electric fields to propel electrons and their antiparticles to high energies. These particles emit synchrotron radiation as they pass through magnetic fields.
The dependency of the intensity of this radiation upon spin polarizes the electron beam—a process known as the Sokolov—Ternov effect.
Synchrotron radiation can also cool the electron beams to reduce the momentum spread of the particles. Electron and positron beams are collided upon the particles' accelerating to the required energies; particle detectors observe the resulting energy emissions, which particle physics studies.
Low-energy electron diffraction LEED is a method of bombarding a crystalline material with a collimated beam of electrons and then observing the resulting diffraction patterns to determine the structure of the material.
The electron microscope directs a focused beam of electrons at a specimen. Some electrons change their properties, such as movement direction, angle, and relative phase and energy as the beam interacts with the material.
Microscopists can record these changes in the electron beam to produce atomically resolved images of the material. This wavelength, for example, is equal to 0.
However, electron microscopes are expensive instruments that are costly to maintain. Two main types of electron microscopes exist: transmission and scanning.
Transmission electron microscopes function like overhead projectors , with a beam of electrons passing through a slice of material then being projected by lenses on a photographic slide or a charge-coupled device.
Scanning electron microscopes rasteri a finely focused electron beam, as in a TV set, across the studied sample to produce the image.
The scanning tunneling microscope uses quantum tunneling of electrons from a sharp metal tip into the studied material and can produce atomically resolved images of its surface.
In the free-electron laser FEL , a relativistic electron beam passes through a pair of undulators that contain arrays of dipole magnets whose fields point in alternating directions.
The electrons emit synchrotron radiation that coherently interacts with the same electrons to strongly amplify the radiation field at the resonance frequency.
FEL can emit a coherent high- brilliance electromagnetic radiation with a wide range of frequencies, from microwaves to soft X-rays.
These devices are used in manufacturing, communication, and in medical applications, such as soft tissue surgery.
Electrons are important in cathode ray tubes , which have been extensively used as display devices in laboratory instruments, computer monitors and television sets.
However, they have been largely supplanted by solid-state devices such as the transistor. From Wikipedia, the free encyclopedia.
Subatomic particle with negative electric charge. For other uses, see Electron disambiguation. Hydrogen atomic orbitals at different energy levels.
The more opaque areas are where one is most likely to find an electron at any given time. See also: History of electromagnetism.
See also: The proton—electron model of the nucleus. See also: History of quantum mechanics. Main article: Virtual particle.
Main article: Atom. Electronics portal Physics portal Science portal. See: Gupta Assume that the electron's charge is spread uniformly throughout a spherical volume.
Since one part of the sphere would repel the other parts, the sphere contains electrostatic potential energy.
Setting them equal and solving for r gives the classical electron radius. See Zombeck In other words, the projections of the spins of all electrons onto their momentum vector have the same sign.
Physical Review Letters. Bibcode : PhRvL.. Annals of Science. University of Chicago Press. Histories of the Electron: The Birth of Microphysics.
MIT Press. Philosophical Magazine. National Institute of Standards and Technology. Gaithersburg, MD: U.
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