Chemistry - f-block Question with Solution | TestHub

f-subshell contains seven orbitals in it. Hence, if seven electrons are present in these orbitals then it said to be half-filled. Electronic configuration of all the elements are:

$\mathrm{Sm}(Z=62)=4f^6 {\mathrm{s}}^2$

$\mathrm{Eu}(Z=63)=4{\mathrm{f}}^{7}6{\mathrm{S}}_2$

$\mathrm{Tb}(Z=65)=4{\mathrm{f}}^{9}6{\mathrm{s}}^2$

$\mathrm{Gd}(\mathrm{Z}=64)=4{\mathrm{f}}^{7}5{\mathrm{d}}^{1}6{\mathrm{s}}^2$

$Pm(Z=61)=4{\mathrm{f}}^{5}6{\mathrm{s}}^2$

So, $\mathrm{Eu}$ & $\mathrm{Gd}$ have half-filled configuration.