Pauli Exclusion Principle

(noun)

The quantum mechanical principle that no two identical fermions (particles with half-integer spin) may occupy the same quantum state simultaneously.

Examples of Pauli Exclusion Principle in the following topics:

  • The Pauli Exclusion Principle

    • The Pauli exclusion principle states that no two fermions can have identical wavefunctions.
    • The Pauli exclusion principle, formulated by Austrian physicist Wolfgang Pauli in 1925, states that no two fermions of the same kind may simultaneously occupy the same quantum state.
    • The Pauli exclusion principle explains a wide variety of physical phenomena.
    • However, according the the Pauli Exclusion Principle, when there are two in a state, there must be one of each.
    • Illustrate how the Pauli exclusion principle partially explains the electron shell structure of atoms.

  • The Building-Up (Aufbau) Principle

    • The Aufbau principle determines an atom's electron configuration by adding electrons to atomic orbitals following a defined set of rules.
    • According to the principle, electrons fill orbitals starting at the lowest available energy states before filling higher states (e.g., 1s before 2s).
    • According to the Pauli Exclusion Principle, two electrons in an orbital will not spin the same way.
    • The Aufbau principle is based on the idea that the order of orbital energies is fixed—both for a given element and between different elements.
    • This assumption is approximately true—enough for the principle to be useful—but not physically reasonable.

  • Electron Configurations and Magnetic Properties of Ions

    • The Aufbau principle (from the German Aufbau, meaning "building up, construction;" also called the Aufbau rule or building-up principle) is used to determine the electron configuration of an atom, molecule, or ion.
    • The principle postulates a hypothetical process in which an atom is "built up" by the progressive addition of electrons.
    • According to the principle, electrons fill orbitals starting at the lowest available energy state before filling higher states (e.g., 1s before 2s).
    • The number of electrons that can occupy each orbital is limited by the Pauli exclusion principle.

  • Bonding and Antibonding Molecular Orbitals

    • The Aufbau principle states that orbitals are filled starting with the lowest energy
    • The Pauli exclusion principle states that the maximum number of electrons. occupying an orbital is two, with opposite spins.

  • Mechanistic Background

    • The principles set forth in the UV-Visible Spectroscopy chapter will provide a helpful foundation.
    • Condon to formulate the Franck-Condon Principle: Electronic transitions occur much faster than nuclei can respond.
    • The Franck-Condon principle requires that excitation occur by a vertical transition, shown by the red line, resulting in the population of higher vibrational levels in the excited state.
    • Electronic states in which two electrons with identical spin occupy different orbitals (the Pauli exclusion principle) have a net spin of 1 (2 • 1/2) and are paramagnetic.

  • Quantum Numbers

    • Each electron in any individual orbital must have different spins because of the Pauli exclusion principle, therefore an orbital never contains more than two electrons.