electron (redirected from electron micrographs)

electron, elementary particle carrying a unit charge of negative electricity. Ordinary electric current is the flow of electrons through a wire conductor (see electricity). The electron is one of the basic constituents of matter. An atom consists of a small, dense, positively charged nucleus surrounded by electrons that whirl about it in orbits, forming a cloud of charge. Ordinarily there are just enough negative electrons to balance the positive charge of the nucleus, and the atom is neutral. If electrons are added or removed, a net charge results, and the atom is said to be ionized (see ion). Atomic electrons are responsible for the chemical properties of matter (see valence). The name electron was first used for a unit of negative electricity by the English physicist G. J. Stoney in the late 19th cent. The actual discovery of the particle, however, was made in 1897 by J. J. Thomson, who showed that cathode rays are composed of electrons and who measured the ratio of charge to mass for the electron. In 1909, R. A. Millikan measured the charge of the electron. Combining these two results gives the mass of the electron (about 1/1,840 of the mass of the proton). Ernest Rutherford, in 1903, showed that beta rays (see radioactivity) are high-energy electrons. In 1927, Davisson and Germer, working with high-speed electron beams, discovered that electrons sometimes exhibit the wave property of diffraction. This confirmed L. V. de Broglie's hypothesis that electrons, which had previously been thought of as particles, also possess certain wave properties (see quantum theory). The wavelike properties of electrons are utilized in the electron microscope and other devices. The electron is the lightest particle having a non-zero rest mass. It belongs to the lepton class of particles and, together with its antiparticle, the positron, and its associated neutrino and antineutrino, constitutes a subfamily of the leptons. In any particle reaction involving any of the four members of the electron family, the total electron family number (+1 for ordinary particles, −1 for antiparticles) must be conserved (see conservation laws, in physics). As a consequence, an electron and a positron (total electron family number equals zero) can annihilate each other to yield two or more photons or a neutrino-antineutrino pair, but not two neutrinos (total electron family number equals two).

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electron

Lightest electrically charged subatomic particle known. It carries a negative charge (see electric charge), the basic charge of electricity. An electron has a small mass, less than 0.1% the mass of an atom. Under normal circumstances, electrons move about the nucleus of an atom in orbitals that form an electron cloud bound in varying strengths to the positively charged nucleus. Electrons closer to the nucleus are held more tightly. The first subatomic particle discovered, the electron was identified in 1897 by J. J. Thomson.

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electron

An elementary particle that orbits the nucleus of an atom. There is one electron for every proton in the nucleus, which keeps the atom "electrically neutral," as electrons are considered to have a negative charge and protons a positive charge.

Electron Imbalance Creates a Charge
When the number of electrons and protons are unequal, the atom is electrically charged. If there are more electrons than protons, it is negatively charged; if fewer electrons, it is positively charged. Electrical generators strip electrons away from their atoms to provide electricity, and electrons are removed, as well as added, to enable other electrical effects (see ion and n-type silicon). See atom, wave-particle duality and photon.

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electron

a stable elementary particle present in all atoms, orbiting the nucleus in numbers equal to the atomic number of the element in the neutral atom; a lepton with a negative charge of 1.602 176 462 × 10^--19 coulomb, a rest mass of 9.109 381 88 × 10^--31 kilogram, a radius of 2.817 940 285 × 10^--15 metre, and a spin of ½

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electron [i′lek‚trän]

(physics)

A stable elementary particle which is the negatively charged constituent of ordinary matter, having a mass of about 9.11 × 10^-28gram (equivalent to 0.511 MeV), a charge of about -1.602 × 10^-19coulomb, and a spin of ½. Also known as negative electron; negatron.

Collective name for the electron, as in the first definition, and the positron.

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Electron

An elementary particle which is the negatively charged constituent of ordinary matter. The electron is the lightest known particle which possesses an electric charge. Its rest mass is m_e ≅ 9.1 × 10^-28 g, about ¹/₁₈₃₆ of the mass of the proton or neutron, which are, respectively, the positively charged and neutral constituents of ordinary matter. Discovered in 1895 by J. J. Thomson in the form of cathode rays, the electron was the first elementary particle to be identified. See Electric charge, Elementary particle, Nuclear structure

The charge of the electron is -e ≅ -4.8 × 10^-10 esu = -1.6 × 10^-19 coulomb. The sign of the electron's charge is negative by convention, and that of the equally charged proton is positive. This is a somewhat unfortunate convention, because the flow of electrons in a conductor is thus opposite to the conventional direction of the current.

Electrons are emitted in radioactivity (as beta rays) and in many other decay processes; for instance, the ultimate decay products of all mesons are electrons, neutrinos, and photons, the meson's charge being carried away by the electrons. The electron itself is completely stable. Electrons contribute the bulk to ordinary matter; the volume of an atom is nearly all occupied by the cloud of electrons surrounding the nucleus, which occupies only about 10^-13 of the atom's volume. The chemical properties of ordinary matter are determined by the electron cloud. See Meson, Radioactivity

The electron obeys the Fermi-Dirac statistics, and for this reason is often called a fermion. One of the primary attributes of matter, impenetrability, results from the fact that the electron, being a fermion, obeys the Pauli exclusion principle; the world would be completely different if the lightest charged particle were a boson, that is, a particle that obeys Bose-Einstein statistics. See Bose-Einstein statistics, Exclusion principle, Fermi-Dirac statistics, Positron

Magnetic moment

The electron has magnetic properties by virtue of (1) its orbital motion about the nucleus of its parent atom and (2) its rotation about its own axis. The magnetic properties are best described through the magnetic dipole moment associated with 1 and 2. The classical analog of the orbital magnetic dipole moment is the dipole moment of a small current-carrying circuit. The electron spin magnetic dipole moment may be thought of as arising from the circulation of charge, that is, a current, about the electron axis; but a classical analog to this moment has much less meaning than that to the orbital magnetic dipole moment. The magnetic moments of the electrons in the atoms that make up a solid give rise to the bulk magnetism of the solid.

Spin

That property of an electron which gives rise to its angular momentum about an axis within the electron. Spin is one of the permanent and basic properties of the electron. Both the spin and the associated magnetic dipole moment of the electron were postulated by G. E. Uhlenbeck and S. Goudsmit in 1925 as necessary to allow the interpretation of many observed effects, among them the so-called anomalous Zeeman effect, the existence of doublets (pairs of closely spaced lines) in the spectra of the alkali atoms, and certain features of x-ray spectra. See Spin (quantum mechanics)

The spin quantum number is s, where s is always ½. This means that the component of spin angular momentum along a preferred direction, such as the direction of a magnetic field, is ± ½ℏ, where ℏ is Planck's constant h divided by 2π. The spin angular momentum of the electron is not to be confused with the orbital angular momentum of the electron associated with its motion about the nucleus. In the latter case the maximum component of angular momentum along a preferred direction is lℏ, where l is the angular momentum quantum number and may be any positive integer or zero. See Quantum numbers

The electron has a magnetic dipole moment by virtue of its spin. The approximate value of the dipole moment is the Bohr magneton μ₀ which is equal to eh/4πmc = 9.27 × 10^-21 erg/oersted, where e is the electron charge measured in electrostatic units, m is the mass of the electron, and c is the velocity of light. (In SI units, μ₀ = 9.27 × 10^-24 joule/tesla.) The orbital motion of the electron also gives rise to a magnetic dipole moment μ_l, that is equal to μ₀ when l = 1.

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(electronics)

electron - A sub-atomic particle with a negative quantised charge. A flow of electrical current consists of the unidirectional (on average) movement of many electrons. The more mobile electrons are in a given material, the greater it electrical conductance (or equivalently, the lower its resistance).