21 Chemistry -- Atomic Structure

Write short notes on:a.    Hund’s rule of maximum multiplicity b.    Pauli’s exclusion principle

Write short notes on:

a.    Hund’s rule of maximum multiplicity

b.    Pauli’s exclusion principle

a. Hund’s rule of maximum multiplicity

Hund proposed a rule of filling of de-generate orbitals (having equivalent energy) with electrons known as Hund's rule of maximum multiplicity. 

It states: 
In the orbitals of same sub-energy level (sub-orbitals), electrons are filled single first (in the same spin) before filling up fully in pair. 
The electrons prefer to occupy separate orbitals rather than getting paired in the same orbital.

b. Pauli's Exclusion principle: 

Pauli put forward a principle that imposes some restrictions on values of quantum numbers of electrons in a atom, thus giving its name Exclusion Principle. 

It states that: 
No two electrons in an atom can have the same set of four quantum numbers. 

It signifies that: 
1. no two electrons have same spin in an orbital. 
2. an orbital can accommodate not more than two electrons. (since there are only two s quantum numbers)
3. It supports the Bohr-Bury rule of 2n2 for accommodation of no. of electrons in each shell.



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