Pauli exclusion principle is one of the important principles along with Aufbau’s Principle and Hund’s Rule in chemistry. Learning about it is crucial for students especially when they are studying about electrons. It basically helps us to understand the electron arrangements in atoms and molecules and it also gives an explanation for the classification of elements in the periodic table.

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). There are two salient rules that the Pauli Exclusion Principle follows:

1)Only two electrons can occupy the same orbital.

2)The two electrons that are present in the same orbital must have opposite spins or it should be antiparallel.

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 this.

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