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electron tracks
Electron tracks. Credit: CERN
A negatively charged subatomic particle with a mass equal to 1/1837 that of a proton or 9.1091 × 10-31 kg and a charge of 1.6021 × 10-19 coulombs. Very roughly, a trillion electrons would weigh about as much as a speck of dust. Electrons are fermions. Like all other fermions, the electron has no known internal structure. It behaves as if it has zero radius. The antiparticle of the electron is the positron. Fast moving streams of electrons emitted during radioactive decay are known as beta particles.

Electrons occur in the outer parts of atoms, in orbitals corresponding to definite fixed energies. When an electron in an atom jumps from one particular orbital to another it gives rise to the emission or absorption of electromagnetic radiation at a specific characteristic wavelength. All chemical properties of atoms and molecules are determined by the electric interactions of electrons with each other and with the atomic nuclei.

The name "electron" was first suggested by G. Johnstone Stoney in 1891 for the natural unit of electricity. The particle that plays this role was discovered by J. J. Thomson in 1897. "Electron", "electricity", etc., derive from the term "electrica", coined by William Gilbert in 1600 to denote substances such as amber (electrum in Greek) that attract light objects when rubbed.

The wavelength of the electron

Until 1923 the electron was considered to be a particle only, but in that year Louis de Broglie proposed a new theory of the electron (see de Broglie and matter waves). De Broglie proposed that a moving particle, whatever its nature, has wave properties associated with it. The wavelength λ associated with any moving particle of mass m and velocity v, he proposed, is given by λ = h/mv where h is Planck's constant. The first experimental support for de Broglie's ideas came from the Davisson and Germer experiment. to

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