What Are Electrons?

Electrons are elementary subatomic particles that carry a negative electric charge and are constituents of all atoms. They belong to the lepton family in the Standard Model of particle physics, meaning they are not composed of smaller components. Each electron carries a charge of approximately -1.602 × 10⁻¹⁹ coulombs, a value defined as the elementary unit of electric charge, and a rest mass of about 9.109 × 10⁻³¹ kilograms, roughly 1/1836 that of a proton. In atoms, electrons occupy orbitals around the nucleus, and the configuration of these orbitals determines the chemical properties of each element.

The electron was identified as a discrete particle by J.J. Thomson in 1897, and its fundamental role in electrical conduction, chemistry, and radiation was established over the following decades. The U.S. Department of Energy's science explainer on electrons notes that electrons behave as both particles and waves, a duality central to quantum mechanics and directly relevant to their application in electron microscopes and modern integrated circuits.

Quantum Mechanical Properties

The behavior of electrons is governed by quantum mechanics, formalized in the non-relativistic case by the Schrödinger equation, which describes the probability distribution of finding an electron at a given location and energy state. Electrons possess an intrinsic angular momentum called spin, quantized as ±ħ/2, making them fermions. As fermions, no two electrons can occupy the same quantum state simultaneously, in accordance with the Pauli exclusion principle, which underpins the structure of the periodic table and the band theory of solids. Elementary particle exchange interactions describe the forces between electrons mediated by virtual photons in the framework of quantum electrodynamics (QED), the most precisely tested theory in physics. The binding of electrons to nuclei and the formation of chemical bonds are governed by the balance between electrostatic attraction and quantum mechanical confinement energy, with these principles documented rigorously in the NIST Atomic Spectra Database.

Electron Accelerators and High-Energy Applications

Electron accelerators are devices that use electric and magnetic fields to impart kinetic energy to electron beams for research and industrial purposes. Linear accelerators (linacs) and circular machines such as synchrotrons accelerate electrons to relativistic speeds. Synchrotron radiation, emitted when relativistic electrons are bent by magnetic fields, produces intense, tunable X-ray beams used in materials science, structural biology, and semiconductor lithography. Beta rays, one of the three classical forms of radioactive decay, consist of electrons (or positrons) emitted from unstable atomic nuclei; their study contributed foundational evidence for the neutrino hypothesis. Cosmic rays interacting with the upper atmosphere generate secondary electron-positron pairs among other products, contributing to the high-energy particle flux studied in astrophysics and particle physics. Electron beam processing, including electron beam welding and sterilization, relies on focused, high-energy electron streams, with research on these applications archived through IEEE Xplore.

Electrons in Electrical Engineering

In conduction materials, the flow of free electrons constitutes electric current. The charge-to-mass ratio and the mobility of electrons in semiconductor materials determine the performance of transistors and diodes. Quantum tunneling, in which electrons pass through potential barriers that classical mechanics would forbid them to cross, is exploited in tunnel diodes, flash memory cells, and scanning tunneling microscopes. Photoemission, the ejection of electrons from a material by absorbed photons, underlies photodetectors, solar cells, and photomultiplier tubes.

Applications

Electrons and their controlled use have applications in a wide range of fields, including:

• Electrical and electronic circuits, where electron flow constitutes current in conductors and semiconductors
• Electron microscopy, enabling imaging at sub-nanometer resolution
• Radiation therapy, where electron beams treat superficial tumors
• Synchrotron light sources for materials characterization and protein crystallography
• Electron beam lithography for nanofabrication of semiconductor devices