| electron | |
|---|---|
| Name | Electron |
| Generation | 1st |
| Family | Lepton |
| Electric charge | −1 e |
| Spin | 1/2 |
| Mass | 9.10938356×10^−31 kg |
| Discovered | 1897 |
| Discoverer | J. J. Thomson |
electron
The electron is a fundamental subatomic leptonic particle with negative electric charge and intrinsic spin 1/2, central to the structure of atoms, the properties of matter, and many phenomena in Quantum physics. Electrons underpin chemistry, condensed matter physics, and much of modern technology through their quantum behavior, interactions described by quantum electrodynamics, and controllable quantum states used in quantum information.
The discovery of the electron is credited to J. J. Thomson in 1897 following cathode ray experiments at the Cavendish Laboratory that established a particle smaller than atoms. Earlier observations by William Crookes and studies of cathode rays informed Thomson's measurements of charge-to-mass ratio. The name "electron" had been proposed by George Johnstone Stoney. Subsequent experiments by Robert A. Millikan (the Millikan oil-drop experiment) measured the elementary charge, confirming quantization of charge. Developments in atomic theory—including the Rutherford model and Bohr model—placed the electron at the center of evolving models of atomic structure, later superseded by quantum mechanics.
Electrons are members of the first generation of fermions in the Standard Model, categorized as leptons. They carry a fundamental negative charge equal in magnitude to the proton's positive charge, measured as the elementary charge e. The rest mass of the electron is approximately 9.109×10^−31 kg (≈511 keV/c^2). As spin-1/2 particles they obey the Pauli exclusion principle and Fermi–Dirac statistics, which determine the structure of atoms and the electronic properties of solids. The electron's magnetic moment exhibits a small anomalous component precisely predicted by quantum electrodynamics and measured in experiments involving Penning traps and precision spectroscopy.
In nonrelativistic quantum mechanics, an electron is described by a complex wave function governed by the Schrödinger equation; wavefunctions yield probability amplitudes for position and momentum per the Born rule. The electron's spin requires a two-component spinor formalism and interaction with electromagnetic potentials via Pauli equation in the nonrelativistic limit. Relativistically, the electron is described by the Dirac equation, formulated by Paul Dirac, which predicts antiparticles and correctly accounts for spin and fine-structure effects. The Dirac formalism led to the prediction and discovery of the positron by Carl Anderson. Quantum descriptions incorporate operators for observables, commutation relations, and concepts such as entanglement and quantum tunnelling that are central to electron behavior in microscopic systems.
Electron interactions with the electromagnetic field are described by quantum electrodynamics (QED), a quantum gauge theory based on the U(1) gauge symmetry of electromagnetism. In QED, electrons are excitations of the electron field and interact via the exchange of virtual photons; perturbative calculations use Feynman diagrams and renormalization techniques developed by Richard Feynman, Julian Schwinger, and Sin-Itiro Tomonaga. The electron participates in weak interactions via electroweak theory, sharing left-handed doublets with the electron neutrino through W and Z bosons. Precision tests of QED include measurements of the anomalous magnetic dipole moment and Lamb shift in hydrogen atom spectroscopy.
Electrons occupy quantized energy levels in atoms described by atomic orbitals (solutions to the Schrödinger or Dirac equation in a central potential). The arrangement of electrons in electron shells and subshells underlies the periodic table and valence chemistry. Electron exchange and overlap of orbitals produce covalent bonds described by molecular orbital theory and valence bond theory, while ionic bonding follows from electrostatic interactions. In solids, electrons form bands per band theory of solids; phenomena such as conductivity, semiconductors, superconductivity, and magnetism arise from collective electronic states influenced by electron correlation and Fermi surface topology. Electron pairing and Cooper pair formation are central to BCS theory of superconductivity.
Electrons are observed and manipulated using devices such as cathode ray tubes, electron microscopes (TEM and SEM), and particle detectors like cloud chambers and Geiger–Müller tubes. Precision measurements employ Penning traps, Paul traps, and atomic beam methods; spectroscopic techniques (e.g., photoelectron spectroscopy and ARPES) probe electronic structure. Scattering experiments at facilities such as CERN and DESY probe high-energy electron interactions. Quantum transport experiments in quantum Hall effect setups and single-electron transistors reveal fundamental charge quantization and coherence.
Electrons are exploited in electronics (diodes, transistors, integrated circuits) forming the basis of modern computing and communication technologies. Electron beams are central to electron microscopy for nanoscale imaging and to STM for surface studies and manipulation of single atoms. Controlled electron states power spintronics and quantum computing approaches using quantum dots, superconducting qubits involve electron pairing, and topological insulator research depends on electronic surface states. Applications extend to synchrotron radiation sources, free-electron lasers, and medical technologies such as radiotherapy that use high-energy electron beams. Advances in controlling electron coherence, spin, and entanglement continue to drive research at institutions like MIT, Stanford University, Max Planck Society, and national laboratories worldwide.
Category:Subatomic particles Category:Quantum physics Category:Leptons