Pauli principle

The Pauli principle, or Paulian exclusion principle, is a law in physics, more precisely in the field of quantum physics. The discovery of the Pauli principle goes back to the Austrian scientist Wolfgang Ernst Pauli, who in 1925 formulated one of the most fundamental principles of quantum mechanics.

Small Reminder: Quantum mechanics deals with the laws and states of matter and how their physical properties can be calculated (in the size range of atoms and below). That makes the Pauli principle especially relevant for chemistry.

Derivation of the Pauli Principle

Basically, the definition of the Pauli principle is beyond the normalizations that apply in classical physics. This is based on the assumption that at no time can it be determined whether two particles in an atom are in the same place or not. The logical consequence: they are initially indistinguishable.

As experiments show, for orbitals (extended areas with multiple particles) one can determine a probability of where the electrons are located. These areas overlap occasionally so that the particles can also be in the same location.

Definition of the Pauli Principle

This is where the Pauli principle of physics comes in: Two electrons can never have the same quantum numbers. These measures of the motion properties of an electron provide information about orbital, angular momentum and spin. The Pauli principle fixes that two electrons must differ in at least one of their quantum numbers. It therefore applies to all particles with half-integer spin, called fermions. These include not only electrons but also protons and neutrons. So-called bosons, which are responsible for the transfer of forces, are not subject to the Pauli principle.

The consequence of the Pauli principle

By characterizing the fermions in the Pauli principle, it can be proved that only two electrons can always find space in an orbital. From today's point of view, this means that when one commutes identical fermions, the wave function of a quantum system becomes antisymmetric. Thus, accurate conclusions can be drawn about the structure and the differentiation (Periodic Table) of matter. In addition, the exchange interaction of the electrons, which defines the Pauli principle, is responsible for the magnetism.