Write the electronic configuration of gadlonium with Z= 64 and predict the sum of the spins of unpaired electrons.

Explanation

The electronic configuration of Eu (Z= 63 ) in accordance with aufbau principle is `= [Xe]^(54) 6s^(2) 4f^(7) 5d^(10)` . The next electron (i.e., 64 th ) as expected does not go to 4f- subshell but goes to 5- subshell due to greater stability of the exactly half- filled 4f- subshell. Thus , the electronic configuration of gadlonium (Z= 64 ) =`[Xe ] 6s^(2) 4f^(7) 4d^(1)` . Although here the last electron goes to 5d- orbital , still it is not called d- block element but is called f-block element since the inner 4f- subshell is still not fully filled. Now Gd (Z=64) has eight half - filled orbitals i.e., seven 4f and one 5d therefore the sum of the spins of unpaired electron `= 8 xx (1)/(2) =4`