Electron
In the early 1830s, Michael Faraday carried out a series of historic experiments on electrolysis. He found that a given amount of electrical current always liberates a given amount of any substance. One conclusion that Faraday drew from these results was that electricity might consist of "atoms of charge." James Clerk Maxwell used the term "molecular charge of electricity" to describe Faraday's results, but doubted that "particles" of electricity really existed.
The most clear-cut statement of this concept was made by the Irish physicist, G. Johnstone Stoney in 1874. Stoney said that electrolysis could best be understood by thinking in terms of "units of electricity." Nearly twenty years later, in 1891, Stoney proposed the name electron for this unit of electricity.
Faraday's original analysis of "atoms of charge" received a mixed response from colleagues. To many scientists, Faraday's results and those of Svante August Arrhenius on solution chemistry seemed to lead to some particle interpretation. Others, however, rejected this explanation, preferring to suppose that some unusual form of electromagnetic wave was involved.
A turning point in the debate occurred as a result of the studies on cathode rays conducted by William Crookes and Arthur Schuster in the mid-1870s. The deflection of cathode rays by magnetic fields convinced Crookes, Schuster, and many of their colleagues that electricity actually consists of a stream of charged particles.
Final resolution of this matter came in 1897 as a result of Joseph J. Thomson's analysis of cathode rays. Thomson was able to deflect the rays with both electrical and magnetic fields and, in the process, to determine the ratio of charge to mass (e/m) for the particles that make up cathode rays. Based on Stoney's earlier measurement of the value for the basic "unit" of electrical charge, e, Thomson then calculated the mass of the electron to be roughly 1.5 x 10-28 g. Thomson adopted Stoney's name of "electron" for this particle.
Research by Hendrik Lorentz, Philipp Lenard, and others provided better values for both the electronic charge and mass. Within a decade, it was clear that the electron was a fundamental elementary particle involved in a wide variety of phenomena including not only familiar electrical events, but also the photoelectric effect, thermionic emission, and radioactivity.
Precise measurements of the electronic charge were made in 1909 by Robert A. Millikan in the United States and F. Ehrenhaft in Austria. Both researchers found ways to calculate the electric charge on a single tiny particle, an oil droplet in Millikan 's case, and a suspended particle, in that of Ehrenhaft. Millikan 's result, 4.774 x 10-10 electrostatic units, was accepted as correct until 1928, when the electronic charge was determined even more precisely by E. Bäcklin in Sweden and J. A. Bearden in the United States.
By the mid-1920s, a number of physicists began to apply wave and quantum theory to the electron. In 1924, for example, Louis Victor de Broglie suggested that electrons have wave properties as well as particle properties. De Broglie's theory was confirmed in 1927 when Clinton Davisson, L. Germer, and G. P. Thomson were able to diffract electron waves.
At about the same time, theoretical calculations by Paul Adrien Maurice Dirac suggested that electrons should possess an intrinsic property known as "spin." Dirac's proposal provided a theoretical basis for an empirical suggestion made somewhat earlier by S. Goudsmit and G. Uhlenbeck to account for the fine structure of spectral lines.
Dirac's theoretical calculations also suggested the existence of an antiparticle to the electron, a particle identical to the electron in every way except for its charge. That particle, named the positron, was discovered in 1932 By Carl David Anderson during his study of cosmic rays.
Today, the electron is regarded as one of the handful of fundamental particles, particles that can not be broken down into anything simpler and that have no structure. It is one of the simplest forms of the fundamental particle family known as the lepton s.
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