Contents
Electron
From Wikipedia, the free encyclopedia
Composition: Elementary particle[2]
Family: Fermion
Group: Lepton
Generation: First
Interaction: Gravity, Electromagnetic, Weak
Antiparticle: Positron (also called antielectron)
Theorized: Richard Laming (1838–51),[3]
G. Johnstone Stoney (1874) and others.[4][5]
Discovered: J.J. Thomson (1897)[6][7]
Symbol(s): e−, β−
Mass: 9.10938215(45)×10−31 kg[8][9]
5.485 799 0943(23) × 10−4 u[10]
1⁄1,822.88850204(77) u[note 1]
0.510998910(13) MeV/c2[11][9]
Electric charge: −1 e[note 2]
−1.602176487(40)×10−19 C[12][9]
Magnetic moment: −1.001 159 652 181 11(74) μB[13][9]
Spin: 1⁄2
The electron is an elementary subatomic particle that carries a negative electrical charge.[14] The concept of a quantum of electrical charge had been theorized on several occasions beginning in 1838, including by Irish physicist George Johnstone Stoney in 1874, who introduced the name electron in 1894.[15][4][5] The electron was first identified in 1897 by J.J. Thomson and his team of British physicists.[6][7] These charged particles, together with the protons and neutrons that comprise atomic nuclei, make up atoms. Electron–electron interaction between atoms is the main cause of chemical bonding. Electrons play an essential role in many physical phenomena such as electricity, magnetism, and thermal conductivity.[16]
Electrons are believed to be point particles with no apparent substructure.[2] They are identical particles that belong to the first generation of the lepton particle family. Each electron carries a negative elementary charge and participates in electromagnetic and weak interactions. The components of its spin, or intrinsic angular momentum, can have values of ±ħ⁄2, where ħ is the reduced Planck constant. For this reason electrons are classified as spin-1⁄2 particles. The mass of an electron is approximately 1⁄1836 of that of the proton.[17][18]
The properties of the electron are determined by its interaction with other particles. The attractive Coulomb force between an electron and proton is what causes electrons to be bound into atoms. When an electron is in motion, it both generates a magnetic field and is deflected by external magnetic fields. Electrons have quantum mechanical properties of both a particle and a wave, so they can collide with other particles and be diffracted like light. While an electron is undergoing acceleration, it can absorb or radiate energy in the form of photons. It can be annihilated by a collision with a positron, the electron's antiparticle, or an electron–positron pair can be produced from gamma ray photons with a combined energy at least equal to the energy at rest of the particles.[18]
Etymology
The ancient Greeks noticed that amber, a gemstone that is formed from the hardened sap of trees, attracted small objects when rubbed with fur; apart from lightning this phenomenon was man's earliest experience of electricity.[19] In his 1600 treatise De Magnete, the English physician William Gilbert coined the New Latin term electricus, to refer to this property of attracting small objects after being rubbed.[20] Both electric and electricity are derived from the Latin ēlectrum, which in turn came from the Greek word ēlektron (ήλεκτρον) for amber. The English name electron is a combination of the word electric and the suffix -on, with the latter now used to designate a subatomic particle.[21][22]
History
As early as 1838–51, the British natural philosopher Richard Laming conceived the idea that an atom is composed of a core of matter surrounded by subatomic particles that had unit electrical charges.[3] Beginning in 1846, German physicist William Weber theorized that electricity was composed of positively and negatively charged fluids, and their interaction was governed by the inverse square law. After studying the phenomenon of electrolysis in 1874, the Irish physicist George Johnstone Stoney suggested that there existed a "single definite quantity of electricity", the charge of a monovalent ion. He was able to estimate the value of this elementary charge e of by means of Faraday's laws of electrolysis.[23] However, Stoney believed these charges were permanently attached to atoms and could not be removed. In 1881, 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".[4]
In 1894, Stoney coined the term electron to represent these elementary charges.
In this paper an estimate was made of the actual amount of this most remarkable fundamental unit of electricity, for which I have since ventured to suggest the name electron.
–
However, it was only at the end of the nineteenth century that these various concepts came together to form a unified theory based upon an electron as a fundamental component of matter.[5]
Discovery
During the 1870s, English chemist and physicist Sir William Crookes developed the first cathode ray tube to have a high vacuum inside.[1] He then showed that the luminescence rays appearing within the tube carried energy and moved from the cathode to the anode. 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.[24][25] In 1879, he proposed that these properties could be explained by what he termed 'radiant matter'. He suggested that this was a fourth state of matter, consisting of negatively charged molecules that were being projected with high velocity from the cathode.[26]
The German-born British physicist Arthur Schuster expanded upon Crookes' experiments by placing metal plates in parallel to the cathode rays and applying an electrical potential between the plates. The field deflected the rays toward the positive plate, providing further evidence that the rays carried negative charge. By measuring the amount of deflection for a given level of current, in 1890 Schuster was able to estimate the charge-to-mass ratio of the ray components. However, this produced such an unexpectedly large value that little credence was given to his calculations at the time.[24]
In 1896, British physicist J.J. Thomson, with his colleagues John S. Townsend and H. A. Wilson,[6] performed experiments indicating that cathode rays really were unique particles, rather than waves, atoms or molecules as was believed earlier. Thomson made good estimates of both the charge e and the mass m, finding that cathode ray particles, which he called "corpuscles," had perhaps one thousandth of the mass of the least massive ion known: hydrogen. He showed that their charge to mass ratio, e/m, was independent of cathode material. He further showed that the negatively charged particles produced by radioactive materials, by heated materials and by illuminated materials were universal.[27] The name electron was again proposed for these particles by the Irish physicist George F. Fitzgerald, and it has since gained universal acceptance.[24]
While studying naturally fluorescing minerals in 1896, 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 New Zealand physicist Ernest Rutherford who discovered they emitted particles. He designated these particles alpha and beta, based on their ability to penetrate matter.[28] In 1900, Becquerel showed that the beta rays emitted by radium could be deflected by an electrical field, and that their mass-to-charge ratio was the same as for cathode rays.[29] This evidence strengthened the view that electrons existed as components of atoms.[30][31]