Therefore, further addition of electrons occurs in the lower energy \(4 f\) - orbital till it is exactly half filled at \(Eu \,(Z=63)\)
Thus, the electronic configuration of \(Eu\) is \([ Xe ] \,4 f ^7 \,6 s ^2\), thereafter, addition of next electron does not occur in the more stable exactly half filled \(4 f^7\) shell but occurs in the little higher energy \(5 d\) - orbital.
Thus, the electronic configuration of \(Gd (Z=64)\) is \([X e] \,4 f^7\, 5 d^1 \,6 s^2\)
(નજીકનાં પૂર્ણાંકમાં રાઉન્ડ ઑફ કરો) $\left[ h =6.63 \times 10^{-34}\, Js , c =3.00 \times 10^{8} \,ms ^{-1}\right.$ $,$ $\left. N _{ A }=6.02 \times 10^{23}\, mol ^{-1}\right]$