Class 11 | Structure Of Atom | Pauli's Exclusion Principle

 2. Pauli's Exclusion Principle

 

 

This principle limits the number of electrons that can occupy any orbital of an atom.

Statement : Two electrons in an atom cannot have the same set of all four quantum numbers.

or Only two electrons may exist in the same orbital with three quantum numbers same i.e. the fourth quantum number different and these electrons must have opposite spin.

Consider helium atom which has two electrons in 1s orbital. The four quantum numbers for two electrons in 1s orbital are as follows . 

 

Thus the two electrons in the same atom have different set of quantum numbers which is in accordance with Pauli's exclusion principle.

• Consider Lithium atom with atomic number 3.Hence K shell contains 2 electrons and L shell contains 1 electron.

• The four quantum numbers for three electrons in Lithium atom are as follows .

 

• Thus in an atom any two electrons may have the same value for any of three quantum numbers but the fourth quantum number must be different.