Question

How does Hund’s rule helps in writing electronic configuration of an atom? Explain with a suitable example.

Answer 1

Hund’s rule : 

According to this rule electron pairing in orbitals starts only when all available empty orbitals of the same energy are singly occupied. 

This Hund’s rule helps in writing of electronic configuration of an element.

Example :

1. The electronic configuration of carbon (C) atom (Z = 6) is 1s² 2s² 2p⁶ . 

2. The first four electrons go into the Is and 2s orbitals. 

3. The next two electrons go into separate 2p orbitals, with both electrons having the same spin.

Another example : 

1. The electronic configuration of oxygen (₈O) is 1s²2s²2p⁴ . 

2. The first four electrons go into the 1s, 2s orbitals. 

3. The next four electrons go into 2p orbits as 2 in 2p_x, 1 in 2p_y and 1 in 2p_z orbital.

4. Here pairing of electron in 2p_x starts after filling of electron in each 2p_x, 2p_y, 2p_z orbitals. 

5. But electrons do not occupy like this