exclusion principle

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exclusion principle,

physical principle enunciated by Wolfgang Pauli in 1925 stating that no two electrons in an atomatom
[Gr.,=uncuttable (indivisible)], basic unit of matter; more properly, the smallest unit of a chemical element having the properties of that element. Structure of the Atom
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 can occupy the same energy state simultaneously. The energy states, or levels, in an atom are described in the quantum theoryquantum theory,
modern physical theory concerned with the emission and absorption of energy by matter and with the motion of material particles; the quantum theory and the theory of relativity together form the theoretical basis of modern physics.
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 by various values of four different quantum numbers; the exclusion principle holds that no two electrons can have the same four quantum numbers in an atom. One of these quantum numbers describes one of the two possible directions for the electron's intrinsic spin. As a result of the exclusion principle, two electrons that are in the same energy level as described by the other three quantum numbers are differentiated from each other because they have opposite spins. This principle applies not only to atoms but to other systems containing particles as well, and it applies not only to electrons but also to a large class of particles collectively known as fermions (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 principle

No two electrons may simultaneously occupy the same quantum state. This principle, often called the Pauli principle, was first formulated by Wolfgang Pauli in 1925 and, for time-independent quantum states, it means that no two electrons may be described by state functions which are characterized by exactly the same quantum numbers. In addition to electrons, all known particles having half-integer intrinsic angular momentum, or spin, obey the exclusion principle. It plays a central role in the understanding of many diverse phenomena, including the periodic table of the elements and their chemical activities, the electron contribution to the specific heat of metals, the shell structure in the atomic nucleus analogous to that of electrons in atoms, and certain symmetries in the scattering of identical particles. See Angular momentum, Quantum numbers, Spin (quantum mechanics)

Using the fact that a system will try to occupy the state of lowest possible energy, the electron configuration of atoms may be understood by simply filling the single-particle energy levels according to the Pauli principle. This is the basis of Niels Bohr's explanation of the periodic table. See Atomic structure and spectra, Electron configuration

exclusion principle

See Pauli exclusion principle.

exclusion principle

[ik′sklü·zhən ‚prin·sə·pəl]
The principle according to which two species cannot coexist in the same locality if they have identical ecological requirements.
(quantum mechanics)
The principle that no two fermions of the same kind may simultaneously occupy the same quantum state. Also known as Pauli exclusion principle.
References in periodicals archive ?
When they found it, they discovered that it permits the existence of particles they call "parafermions" or "parons," which can violate the exclusion principle.
The Pauli Exclusion Principle is an extremely important principle in science [10].
Hence, due to the Pauli exclusion principle, all of them have the same antisymmetric space-spin state.
Although physicists commonly invoke the exclusion principle, "you have to measure [its effects] before people really believe it," says Stefan Oberholzer of the University of Basel in Switzerland, where he and his colleagues conducted one of the confirming tests.
Their report proved that with Pauli's exclusion principle, matter is stable; without it, matter collapses into a dense state, creating a situation in which "the assembly of any two macroscopic objects would release energy comparable to that of an atomic bomb.
In the most precise experimental test to date, researchers found no evidence for any violations of the Pauli exclusion principle (137: 287).
Ecologists recognize this as the competitive exclusion principle.