Pauli Exclusion Principle

Pauli exclusion principle states that in a single atom no two electrons will have an identical set or the same quantum numbers (n, l, ml, and ms). To put it in simple terms, every electron should have or be in its own unique state (singlet state). 
It states that:-
*Only two electrons can occupy the same orbital.
*The two electrons that are present in the same orbital must have opposite spins or it should be antiparallel.
However, Pauli Exclusion Principle does not only apply to electrons. It applies to other particles of half-integer spin such as fermions. It is not relevant for particles with an integer spin such as bosons which have symmetric wave functions. Moreover, bosons can share or have the same quantum states, unlike fermions. As far as the nomenclature goes, fermions are named after the Fermi–Dirac statistical distribution that they follow. Bosons, on the other hand, get their name from the Bose-Einstein distribution function.
==History==
An Austrian physicist named Wolfgang Pauli formulated the principle in the year 1925. With this principle, he basically described the behaviour of the electrons. Later in the year 1940, he expanded on the principle to cover all fermions under his spin-statistics theorem. Meanwhile, fermions that are described by the principle include elementary particles such as quarks, electrons, neutrinos, and baryons.
Wolfgang Pauli was also awarded the Nobel prize in the year 1945 for the discovery of the Pauli exclusion principle and his overall contribution in the field of quantum mechanics. He was even nominated by Albert Einstein for the award.
==Use in Chemistry==
In chemistry, the law is mainly used to explain or determine the electron shell structure of atoms and predict which atoms are likely to donate electrons. How does the principle work or where does it apply? Well, if we look at the atoms whenever it gains a new electron or electrons it usually moves to the lowest energy state or it shifts to the outermost shell. If the state has one electron then it can either be spin-up or spin down. Now, if we consider the Pauli exclusion principle if there are two electrons in a state, then each of the electrons will have spin-up or spin down-state but not the same.
==Notes==
The curious double-handed nature of intrinsic Spin is intimately related to the way in which two or more such particles respond to the proximity of others. As a result of their Wave properties, two electrons will probe each other's presence, quite apart from the electric force between them, because the peaks and troughs of one wave will overlap and interfere with the peaks and troughs of the other. A mathematical study of this effect shows that a type of repulsion exists that prevents more than one electron at a time from occupying the same state(ow84)
The Pauli Exclusion principle, it turns out, applies to particles that have a half-integral amount of Spin- particles that have no spin at all (i.e. photons) or integer spin behave in a completely different fashion, following a different set of rules(ssc96)
The reason why metals are so strong, so resistant to pressure, is that because of the Pauli exclusion principle for fermions the Electrons cannot be squeezed tighter together(ssc138)
Category:Quantum Physics
Category:Electron Configuration