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Definition: An electron is a fundamental particle, which means it cannot be broken into smaller particles. Electrons may be bound in the "electron cloud" surrounding an atomic nucleus, or may break free from the cloud as a "free electron."

Electron Details

  • mass of an electron (me) = 9.2095 x 10-31 kg
  • charge of an electron (-e) = -1.602177 x 10-19 C
  • electron rest energy (mec2) = 0.511 MeV
  • spin of an electron = +1/2 or -1/2
The electron is a fermion, which means it has a half-integer spin. Electrons are members of the lepton family of particles.

The antiparticle of the electron is called the positron.

Discovery of the Electron

In 1974, G. Johnstone Stoney theorized the existence of a unit of charge. He coined the term electron to describe such a unit charge in 1894.

The electron was not discovered until 1897, when J.J. Thomson discovered the particle in his research with cathode ray tubes. It was not until 1909 when experimental physicist Robert Millikan calculated the electron's mass in his classic oil-drop experiment.

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