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{{Short description|Elementary particle with negative electric charge}}

{{Quantum matter backlink|Atoms}}

An '''electron''' is a stable subatomic particle with a negative elementary electric charge. It is one of the fundamental components of ordinary matter and belongs to the group of particles known as [[Physics:Quantum lepton|leptons]]. Electrons are generally bound to atomic nuclei by the electromagnetic force and occupy [[Physics:Quantum atoms/orbital|atomic orbitals]] that determine the chemical and physical properties of matter.<ref name="NIST">{{cite web |title=CODATA Value: electron mass |url=https://physics.nist.gov/cgi-bin/cuu/Value?me |publisher=NIST}}</ref>

Electrons can exist freely or bound within atoms. They are responsible for electricity, magnetism, chemical bonding, thermal conductivity, and many optical phenomena. Because electrons are [[Physics:Quantum fermion|fermions]], they obey the [[Physics:Quantum Pauli exclusion principle|Pauli exclusion principle]], which strongly influences the structure of matter.<ref name="Dirac1928">{{cite journal |last=Dirac |first=P. A. M. |title=The Quantum Theory of the Electron |journal=Proceedings of the Royal Society A |year=1928 |volume=117 |pages=610–624}}</ref>

<div style="float:right; border:1px solid #e0d890; background:#fff8cc; padding:6px; margin:0 0 1em 1em; width:420px;">
[[File:Atomic-orbital-clouds spd m0.png|400px]]
<div style="font-size:90%;">Hydrogen atomic orbitals showing electron probability distributions at different energy levels.</div>
</div>

== Description ==
The electron is considered an [[Physics:Quantum elementary particle|elementary particle]], meaning that it has no known internal structure.<ref>{{cite book |last=Griffiths |first=David |title=Introduction to Elementary Particles |publisher=Wiley |year=2008}}</ref> It has a mass of approximately 9.109 × 10<sup>−31</sup> kilograms and an electric charge of −1.602 × 10<sup>−19</sup> coulombs.<ref name="NIST"/>

Electrons exhibit both particle-like and wave-like behavior, a property known as [[Physics:Quantum Wave–particle duality|wave–particle duality]]. Their motion is described by [[Physics:Quantum mechanics|quantum mechanics]], and the probability of finding an electron in a given region is represented by a [[Physics:Quantum mechanics#Wave functions|wavefunction]].<ref>{{cite book |last=Feynman |first=Richard P. |title=The Feynman Lectures on Physics |publisher=Addison-Wesley |year=1964}}</ref>

The electron has an intrinsic angular momentum called [[Physics:Quantum spin|spin]], equal to {{sfrac|1|2}}. This quantum property produces magnetic effects and is fundamental to the behavior of atoms and solids.<ref>{{cite journal |last=Uhlenbeck |first=George |last2=Goudsmit |first2=Samuel |title=Spinning Electrons and the Structure of Spectra |journal=Nature |year=1926 |volume=117 |pages=264–265}}</ref>

== Atomic structure ==
Electrons are bound to positively charged nuclei by the electromagnetic interaction. In atoms, electrons occupy discrete energy levels and orbitals described by solutions of the [[Physics:Quantum Schrödinger equation|Schrödinger equation]].<ref>{{cite journal |last=Schrödinger |first=Erwin |title=Quantisierung als Eigenwertproblem |journal=Annalen der Physik |year=1926}}</ref>

The arrangement of electrons around the nucleus forms the basis of the [[Physics:Periodic table|periodic table]] and determines chemical properties. Electrons in the outermost shell, called [[Physics:Quantum atoms/valence electron|valence electrons]], participate in chemical bonding.<ref>{{cite book |last=Pauling |first=Linus |title=The Nature of the Chemical Bond |publisher=Cornell University Press |year=1960}}</ref>

Electron transitions between energy levels produce absorption and emission spectra characteristic of each element.<ref>{{cite book |last=Bohr |first=Niels |title=On the Constitution of Atoms and Molecules |year=1913}}</ref>

== Quantum properties ==
Electrons obey [[Physics:Quantum Fermi–Dirac statistics|Fermi–Dirac statistics]] and cannot occupy identical quantum states simultaneously. This exclusion principle explains the stability and structure of atoms and condensed matter.<ref>{{cite journal |last=Pauli |first=Wolfgang |title=Über den Zusammenhang des Abschlusses der Elektronengruppen im Atom mit der Komplexstruktur der Spektren |journal=Zeitschrift für Physik |year=1925}}</ref>

The electron magnetic moment is closely related to its spin and is measured with extremely high precision. Quantum electrodynamics predicts the electron magnetic moment with remarkable agreement between theory and experiment.<ref>{{cite journal |last=Schwinger |first=Julian |title=On Quantum-Electrodynamics and the Magnetic Moment of the Electron |journal=Physical Review |year=1948 |volume=73 |pages=416–417}}</ref>

Electrons may become quantum mechanically entangled with other particles, producing correlations that cannot be explained classically.<ref>{{cite journal |last=Einstein |first=Albert |last2=Podolsky |first2=Boris |last3=Rosen |first=Nathan |title=Can Quantum-Mechanical Description of Physical Reality Be Considered Complete? |journal=Physical Review |year=1935 |volume=47 |pages=777–780}}</ref>

== Interactions ==
Electrons interact primarily through the electromagnetic force. Accelerated electrons emit electromagnetic radiation in the form of photons.<ref>{{cite book |last=Jackson |first=John David |title=Classical Electrodynamics |publisher=Wiley |year=1998}}</ref>

An electron and its antiparticle, the [[Physics:Quantum positron|positron]], can annihilate each other to produce gamma rays:

<math>
e^- + e^+ \rightarrow \gamma + \gamma
</math>

This process is important in particle physics, astrophysics, and medical imaging technologies such as positron emission tomography.<ref>{{cite book |last=Perkins |first=Donald |title=Introduction to High Energy Physics |publisher=Cambridge University Press |year=2000}}</ref>

Electrons also participate in weak interactions responsible for radioactive beta decay.<ref>{{cite journal |last=Fermi |first=Enrico |title=Versuch einer Theorie der β-Strahlen |journal=Zeitschrift für Physik |year=1934}}</ref>

== Conductivity ==
In conductive materials such as metals, some electrons become delocalized and form an electron gas capable of moving freely through the material. This motion produces electric current.<ref>{{cite book |last=Ashcroft |first=Neil |last2=Mermin |first2=N. David |title=Solid State Physics |publisher=Brooks Cole |year=1976}}</ref>

In semiconductors, electron transport can be controlled using impurities, electric fields, and quantum structures. Semiconductor electronics form the basis of transistors, integrated circuits, and computers.<ref>{{cite book |last=Sze |first=Simon |title=Physics of Semiconductor Devices |publisher=Wiley |year=2006}}</ref>

Superconductivity occurs when electrons form correlated quantum states known as Cooper pairs, allowing electrical current to flow without resistance.<ref>{{cite journal |last=Bardeen |first=John |last2=Cooper |first2=Leon |last3=Schrieffer |first3=Robert |title=Theory of Superconductivity |journal=Physical Review |year=1957}}</ref>

== Applications ==
Electron beams are widely used in science and technology. Applications include:
* [[Physics:Electron microscope|electron microscopy]]
* [[Physics:Particle accelerator|particle accelerators]]
* [[Physics:Electron beam welding|electron-beam welding]]
* [[Physics:Quantum lithography|electron-beam lithography]]
* [[Physics:Radiation therapy|radiation therapy]]
* [[Physics:Synchrotron radiation|synchrotron radiation]]
* [[Physics:Cathode ray tube|cathode-ray tubes]]

Electrons are also central to modern quantum technologies such as [[Physics:Quantum Computing Algorithms in the NISQ Era|quantum computing]], semiconductor devices, and nanoscale electronics.<ref>{{cite book |last=Nielsen |first=Michael |last2=Chuang |first2=Isaac |title=Quantum Computation and Quantum Information |publisher=Cambridge University Press |year=2010}}</ref>

== History ==
The concept of the electron emerged during studies of electricity and atomic structure in the nineteenth century. In 1897, [[Biography:J. J. Thomson|J. J. Thomson]] demonstrated that cathode rays consisted of negatively charged particles much smaller than atoms.<ref>{{cite journal |last=Thomson |first=J. J. |title=Cathode Rays |journal=Philosophical Magazine |year=1897}}</ref>

In 1909, [[Biography:Robert Millikan|Robert Millikan]] measured the elementary electric charge using the oil-drop experiment.<ref>{{cite journal |last=Millikan |first=Robert |title=On the Elementary Electrical Charge and the Avogadro Constant |journal=Physical Review |year=1911}}</ref>

The development of [[Physics:Quantum mechanics|quantum mechanics]] in the 1920s provided the theoretical framework necessary to understand electron behavior in atoms. [[Physics:Quantum Dirac equation|Dirac's relativistic equation]] later predicted the existence of antimatter and the positron.<ref name="Dirac1928"/>

Experiments throughout the twentieth century confirmed wave–particle duality, spin, quantum statistics, and the role of electrons in atomic and condensed matter physics.<ref>{{cite book |last=Pais |first=Abraham |title=Inward Bound |publisher=Oxford University Press |year=1986}}</ref>

=See also=
{{#invoke:PhysicsQC|tocHeadingAndList|Physics:Quantum basics/See also/Matter}}

=References=
{{reflist|3}}

{{Author|Harold Foppele}}

{{Sourceattribution|Electron|1}}

Physics:Quantum atoms/electron - Revision history

imported>WikiHarold: Complete Matter footer

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