Writethe electronicconfigurationof gadloniumwith Z=64 andpredict thesum of thespins ofunpairedelectrons.

Writethe electronicconfigurationof gadloniumwith Z=64 andpredict thesu

1.	Writethe electronicconfigurationof gadloniumwith Z=64 andpredict thesum of thespins ofunpairedelectrons.
Answer» Solution :The electronicconfigurationof Eu (Z= 63 )in accordance withaufbau principleis `= [Xe]^(54)6s^(2)4f^(7)5D^(10)` . Thenextelectron (i.e.,64 th )as EXPECTED doesnot goto 4f- subshellbut goesto 5- subshell due togreaterstability of theexactly half- filled4f- subshell. THUS ,the electronicconfigurationof gadlonium(Z= 64 ) =`[Xe ] 6s^(2)4f^(7)4d^(1)` . Althoughherethe lastelectron goesto 5d-orbital , still itis not calledd- blockelement butis calledf-blockelement sincethe inner4f- subshellis stillnot fullyfilled.NowGd (Z=64)has eight half - filledorbitalsi.e.,seven4f andone 5d therefore the sum of thespinsof unpaired electron `= 8 xx (1)/(2)=4`