According to Pauli an Orbital Can Hold a Maximum of How Many Electrons?

Aufbau Principle, Pauli's Exclusion Principle, Hund's Rule

Pauli's Exclusion Principle

According to Pauli's Exclusion principle, no two electrons in an atom can have the same set of four quantum numbers. Only two electrons may exist in the same orbital and these electrons must have opposite spin.

There are two rules of the Pauli's Exclusion principle -
1. Two electrons occupy the same orbital
2. Two electrons that are present in the same orbital have opposite spins or are antiparallel.

The Pauli's Exclusion principle not only applies to electrons but also applies to other particles like half-integer spin. The principle was formulated by Wolfgang Pauli in 1925.

Example of Pauli's Exclusion Principle

We take a neutral helium atom as an example of the Pauli's Exclusion principle. In this, the atom is bonded to two electrons and they occupy the outermost shell having opposite signs.

Two electrons are in 1s subshell:
n=1,l=0,ml=0.
If we draw a diagram of a helium atom, then it shows the 1 electron up and 1 down electron.

Importance of Pauli's Exclusion Principle

1.This principle helps to explain many varieties of physical phenomena.
2.It helps to show how the elements participate to form chemical bonds.
3.Periodic table is also described with the help of this rule.

Aufbau Principle

According to the Aufbau principle, the electron is filled in order of increasing energies in its ground state. The atomic orbital with the lowest energy level occupied first as compared to the higher energy level.

The word Aufbau is determined from a German which means construct or built up. The term n represents the principal quantum number and I azimuthal quantum number. The above principle I used to clear the concept of the location of the electron at a different energy level. For example, carbon has 6 electrons so its configuration is 1s² 2s²2p².
It is important to know that each orbital can hold a maximum of two electrons.

There are many exceptions like the electronic configuration of chromium is [Ar] 3d⁵4s¹, and not [Ar] 3d⁴4s². The half-filled subshell shows electron repulsion in the orbital while increasing the stability. Similarly, the filled subshell increases the stability of the atom. That's because many electronic configurations of the atom don't follow Aufbau principle e.g., copper.

Features of the Aufbau Principle

1.According to the Aufbau principle, the lowest energy electron occupies first in the position.
2. Energy of orbital increase can be determined from the n + 1 rule. The sum of principal and mutual quantum numbers determine the different energy levels of the orbitals.
3.The lower n+1 value corresponds to lower orbital energies. If two orbitals share an equal n+1 value, then the orbital with a lower n value is considered as lower energy.
4.Electrons are filled with electrons in the order 1s, 2s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p and so on.

Example of Aufbau Principle

1. The atomic number of sulfur is 16. It means it has 16 electrons.
2. According to the Aufbau principle two of these electrons are present in 1S subshell 8 are present in 2S and 2P subshell whereas remaining electrons are present in 3s and 3p subshell.
3. The electronic configuration is written as 1s² 2s² 2p⁶ 3s² 3p⁴.

Hund's Rule

Hund's rule states that pairing of electrons in the orbitals belonging to the same subshell does not take place until each orbital belonging to that subshell has one electron each. For example, if there are three p, 5 d, and seven f orbitals so the pairing of electrons Starts from p, d, and f orbitals with 4th,6th, and 8 electrons.

In each orbital there is some level that contains two electrons when the electron is filled in these orbitals then the sublevel is filled first with one electron in the same spin. After completing all the sub-levels, the electron field doubles in each level with the opposite sign. For example, for the p orbital, which has three subshells, 3 electrons will be a field in the same spin, and the rest three electrons one by one in the opposite spin of the same sublevels.

Importance of Hund's rule

Hund's rule is important because it specifies the order of filling the electron in a set of the orbital. The orbital filling is a bonded diagram to indicate electron location in a different orbital.

According to Pauli an Orbital Can Hold a Maximum of How Many Electrons?

Source: https://www.aakash.ac.in/important-concepts/chemistry/aufbau-principle-pauli-s-exclusion-principle-hund-s-rule

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