A fundamental particle, denoted e?, where the minus sign indicates that the charge is negative; charge of ?1·602 × 10?19C; mass 9·110 × 10?31 kg or 0·511 MeV, approximately 1/1836 that of the proton; spin ½ fermion; stable against decay; no known size, assumed point-like; no known substructure; a carrier of negative charge in matter, including electrical currents in conductors. Electrons together with the positively-charged nucleus form atoms. They were discovered by J J Thomson in 1897 through studying cathode rays (now called electron beams) in electric and magnetic fields. The charge was determined by Robert Millikan in 1913. Wave-like properties are exhibited in electron diffraction. The electron is associated with weak nuclear force, as in radioactive beta decay, where the beta particle is the electron.
| Electron | |
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Theoretical estimates of the electron density for the first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density |
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| Composition: | Elementary particle |
|---|---|
| Family: | Fermion |
| Group: | Lepton |
| Generation: | First |
| Interaction: | Gravity, Electromagnetic, Weak |
| Antiparticle: | Positron |
| Theorized: | G. Thomson (1897) |
| Mass: |
9.109 3826(16) × 10
5.485 799 0945(24) × 10–4 u
1⁄1822.888 4849(8) u |
| Electric charge: | –1.602 176 53(14) × 10 |
| Spin: | ½ |
The Electron is a fundamental subatomic particle that carries an electric charge.
Within an atom, electrons surround a nucleus composed of protons and neutrons in an electron configuration. The variations in electric field generated by differing numbers of electrons and their configurations in atoms determine the chemical properties of the elements.
Electrons in motion produce an electric current and a magnetic field.
Our understanding of how electrons behave has been significantly modified during the past century, the greatest advances being the development of quantum mechanics in the 20th century. Equally important, particle physics has furthered our understanding of how the electron interacts with other particles.
Classification
The electron is one of a class of subatomic particles called leptons, which are believed to be fundamental particles (that is, they cannot be broken down into smaller constituent parts).
As with all particles, electrons can also act as waves.
The antiparticle of an electron is the positron, which has the same mass but positive rather than negative charge. Anderson, proposed calling standard electrons negatrons, and using electron as a generic term to describe both the positively and negatively charged variants.
Properties and behavior
Electrons have a negative electric charge of −1.6022 × 10 kg based on charge/mass measurements and a relativistic rest mass of about 0.511 MeV/c/1836 of the mass of the proton.
According to quantum mechanics, electrons can be represented by wavefunctions, from which a calculated probabilistic electron density can be determined.
The electron has spin ½ and is a fermion (it follows Fermi-Dirac statistics).
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.
In some superconductors, pairs of electrons move as Cooper pairs in which their motion is coupled to nearby matter via lattice vibrations called phonons. (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 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 (although british physicist Humphrey Maris claims to have found a way to split the electron into "electrinos" using an Electron bubble). However, when a test particle is forced to approach an electron, we measure changes in its properties (charge and mass).
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.
Based on current theory, the speed of an electron can approach, but never reach, c (the speed of light in a vacuum). 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. 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.
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 10130.
In industry
Electron beams are used in welding, lithography, scanning electron microscopes and transmission electron microscopes.
In the laboratory
Electron microscopes are used to magnify details up to 500,000 times.
In theory
In relativistic quantum mechanics, the electron can be described by the Dirac Equation which defines the electron as a (mathematical) point. 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 .
In the Standard Model of particle physics, the electron is the first-generation charged lepton. 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, 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.
Electrons are a key element in electromagnetism, a theory that is accurate for macroscopic systems, and for classical modelling of microscopic systems.
History
The electron as a unit of charge in electrochemistry was posited by G.
The discovery that the electron was a subatomic particle was made in 1897 by J.J.
The electron's charge was carefully measured by Robert Millikan in his oil-drop experiment of 1909.
Quantum electrodynamics| electron | positron | photon |
| self-energy | vacuum polarization | vertex function |
| Gupta-Bleuler formalism | ξ gauge | Ward identities |
| Compton scattering | Bhabha scattering | Moeller scattering |
| anomalous magnetic dipole moment | ||
| positronium | ||
| bremsstrahlung | ||
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