Pauli Principle and Hund’s Rule

Pauli Principle explains that no two electrons will have indistinguishable quantum numbers (n, l, , ml and ms) in a single particle. To put it in straightforward terms, each electron ought to have or be in the singlet state. There are two striking rules that the Pauli Guideline follows: Only two electrons can possess the same orbital. The two electrons that are shown within the same orbital must have inverse spins or they ought to be antiparallel. Each electron will have or be in its own unique energy state. This state is known under this principle as the singlet state.

Particles to Which the Pauli Principle Applies

This principle does not apply to all types of particles. For example, it does not apply to particles with integer spin, which follow a symmetric wave function, such as bosons. Examples of bosons are particles such as photons, gravitons or gluons. However, this principle can also apply to other particles such as fermions (particles with a half-integer spin). The principle also applies to all fermions, including neutrons and protons (derived particles).

State Pauli Exclusion Principle

This principle is broadly used in chemistry, as it helps to determine the shell structure of atoms and to have a clear prediction of the atoms that are more likely to donate electrons. When atoms are donors or acceptors, the electrons bounce from different energy levels in the shell. In the case one state has a single electron, this can have an up or down direction. However, if they are doubly occupied, each electron will have a spin-up or spin-down-state with opposite direction.

Nuclear Stability and the Pauli Exclusion Principle

The nucleus of an atom is made up of particles such as neutrons and protons. Although these subatomic particles are kept inside the orbitals by the nuclear force, they can repel each other. In fact, protons move away from each other thanks to their positive charge that generates electromagnetic force. The forces of attraction and repulsion counteract each other, resulting in the stability of the nucleus. The stability of the nucleus is mainly due to the force exerted by neutrons and protons. This helps to counteract the electrical repulsion between the protons. When this happens, the number of protons increases. In other words, the stability of the nucleus depends on the number of protons and neutrons. The nucleus of an atom is unstable if the number of neutrons is not equal to the number of protons. When this happens, the atoms begin to disintegrate. Pauli’s law is also relevant to understanding the bonding (fusion) and fragmentation (fission) of nucleus. For example, actinides may or may not be fissionable depending on the number of neutrons. If the number is odd, they are usually fissile, while if the number is even, they are usually not. Similarly, if a nucleus has an even number of protons and neutrons, it is usually very stable. Conversely, if the number of protons and neutrons is odd, the nucleus is usually unstable.

Hund’s Rule

Hund’s Rule of Maximum Multiplicity shows that for a given electron arrangement, the term with the most extreme assortment is also the one with the least quantity of energy. This rule relies heavily on the observation of the totality of atomic spectra. These spectra play a central role in predicting the ground state of a molecule with one or more open electronic shells. The rule originated in 1925. As the name suggests, it was discovered by the German scientist Friedrich Hund. Agreeing to Hund matching in p, d and f orbitals cannot happen until each orbital of a given subshell contains one electron each or it is filled with a single electron in each level. This rule describes that:

• In a sublevel, each orbital occupied doubly only after being singly occupied
• The electrons in a singly occupied configuration have the same spin

This means that in steady conditions, the value of spin multiplicity is inversely proportional to the energy embedded in the system. If two or more orbitals have the same summed energy, the available spaces will be individually filled and then by pairs.

Explanation of Hund’s Rule

As mentioned above, electrons occupy a singularly empty orbital before pairing up. This is because the electrons tend to repel each other, as they both have a negative charge. On the other hand, the spin of the initial electron in the sublevel will be responsible for deciding the spin of the other electrons. Thus, all the spins of the electrons occupying the individual orbitals are equal. The chemical properties of an element are largely determined by the valence electrons. In the case where the valence shells of two atoms can come into contact with each other. Moreover, if these layers are not filled, the atom will be more unstable. In fact, elements with similar valence numbers often have similar chemical characteristics. Electron configuration also affects stability. If all the orbitals of an atom are occupied, the atom will be more stable. The most stable orbitals usually have full energy levels. An example of this is noble gasses. Their name comes from the fact that these elements do not react with other elements.