of 5f orbital. The position of Lanthanoids in the periodic table The actual position of Lanthanoids in the periodic table is at group number and period Note XII U4-D-Block-Jerald XII U4-D-Block-Jerald - - - - number .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.
. Lanthanoids have general electronic configuration [Xe] f d s . The common oxidation state of lanthanoides is + . All these elements have similar physical and chemical properties.
Similarly the fourteen elements following actinium resemble in their physical and chemical properties. If we place these elements after Lanthanum in the periodic table below 4d series, the properties of the elements belongs to a group would be different and it would affect the proper structure of the periodic table. Hence a separate position is provided to the inner transition elements as shown in the figure. nitrogen .
N helium He . neon Ne . fluorine F . oxygen .
carbon C . boron B . argon Ar . chlorine Cl .
sulfur S . phosphorus P . silicon Si . aluminium Al .
krypton Kr . bromine Br . selenium Se . arsenic As .
germanium Ge . gallium Ga . zinc Zn . copper Cu .
nickel Ni . cobalt Co . iron Fe . manganese Mn .
chromium Cr . vanadium V . titanium Ti . scandium Sc .
calcium Ca . potassium K . magnesium Mg . sodium Na .
beryllium Be . lithium Li . hydrogen H . xenon Xe .
iodine I . tellurium Te . antimony Sb . tin Sn .