Justify the position of lanthanides and actinides in the periodic table .

Explanation

(i) The actual position of Lanthanoids in the periodic table is at group number 3 and period number 6 .However in the sixth period after lanthanum , the electrons are preferentially filled in inner 4f sub shell and these fourteen elements following lanthanum show similar chemical properties. Therefore these elements are grouped together and placed at the bottom of the periodic table . This position can be justified as follows.
(a) Lanthanoids have general electronic configuratration `[Xe] 4f^(gamma -14) 5d^(0-1) 6s^(2)`
( b) The common oxidation state of lanthanoides is +3
( c ) All these elements have similar (ii) Simiilarly the fourtheen elements following actinium resemble in their physical and chemical properties .
(iii) Similar to lanthanoids activities are also placed in a separate row at the botton of the periodic table.