Hund's Rule, Pauli Exclusion Principle, and the Aufbau Principle - Practice Questions & MCQ

Aufbau Principle -

According to this rule, “orbitals are filled in the increasing order of their energies starting with the orbital of lowest energy”.

Energy of various orbitals are compared with (n+l) rule.

• The orbitals having lower value of (n+l), has lower energy.
• If value of (n+l) is same for two orbitals, then orbital with lower value of ‘n’ would have lower energy and filled first.

For eg: 3p and 3d.

For 3p : n=3, l=1 so n+l= 4           For 3d : n=3, l=2 so n+l=5

Thus energy of 3p is lower than that of 3d.

Pauli Exclusion Principle - 

“No two electrons in an atom can have the same set of four quantum numbers" .

Hund’s Rule of Maximum Multiplicity - 

"pairing of electrons in the orbitals belonging to the same subshell ( p,d or f ) does not take place until each orbital belonging to that subshell has got one electron each i.e. It is singly occupied”.