Chemistry - f-block Question with Solution | TestHub

The elements in which the additional electrons enters $(n-2)f$ orbitals are called inner transition elements. $4f$-block elements are also called lanthanides or rare earths so lanthanides are 14 elements in the sixth period (atomic no. $=58$ to 71 ) that are filling $4f$-sublevel. Related Theory Lanthanoid contraction effect results from poor shielding of nuclear charge (nuclear attractive force on electrons) by 4 felectrons so effective nuclear charge increases; the $6s$ electrons are drawn towards the nucleus, thus resulting in a smaller atomic radius.