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(fûr`mēŏn'): see elementary particleselementary particles,
the most basic physical constituents of the universe. Basic Constituents of Matter

Molecules are built up from the atom, which is the basic unit of any chemical element. The atom in turn is made from the proton, neutron, and electron.
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; exclusion principleexclusion principle,
physical principle enunciated by Wolfgang Pauli in 1925 stating that no two electrons in an atom can occupy the same energy state simultaneously. The energy states, or levels, in an atom are described in the quantum theory by various values of four different
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; Fermi-Dirac statisticsFermi-Dirac statistics,
class of statistics that applies to particles called fermions. Fermions have half-integral values of the quantum mechanical property called spin and are "antisocial" in the sense that two fermions cannot exist in the same state.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



a particle with half-integral spin or an elementary excitation of a quantum system consisting of many particles, that is, a quasiparticle with half-integral spin. Fermions include all baryons—such as the proton, the neutron, and hyperons—and all leptons—the electron, the muon, and neutrinos—and the anti-particles of all baryons and leptons, as well as such quasiparticles as conduction electrons and holes in a solid. Bound systems consisting of an odd number of fermions are also fermions; examples of such systems are atomic nuclei with an odd atomic number and atoms with an odd difference between the atomic number and the number of electrons. The Pauli exclusion principle is valid for fermions. Consequently, systems consisting of identical fermions obey Fermi-Dirac statistics.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


(quantum mechanics)
A particle, such as the electron, proton, or neutron, which obeys the rule that the wave function of several identical particles changes sign when the coordinates of any pair are interchanged; it therefore obeys the Pauli exclusion principle.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

quantum state

A fundamental attribute of particles according to quantum mechanics. The quantum states are primarily x-y-z position, momentum, angular momentum, energy, spin and time.

The shell structures of the atom are made up of fermion particles, which include the protons and neutrons in the nucleus and the electrons in the outer orbits. Fermions cannot share the same quantum state variables. For example, every electron traveling in electric current has a different quantum state than the electron next to it. The fermion was named after Italian physicist Enrico Fermi (1901-1954).

Bosons are particles that can be in the same quantum state. Photons are examples of bosons, and lasers, masers and the superfluidity Helium derive their behavior as a result. The boson, pronounced "bow-son," was named after Indian physicist Satyendra Nath Bose (1894-1974). See quantum mechanics, electron, photon and Higgs boson.
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