5 2 Atomic and
Ionic Sizes
It may be noted that atoms of these elements have electronic
configuration with 6s
2 common but with variable occupancy of 4f level
(Table 4 9) However, the electronic configurations of all the tripositive
ions (the most stable oxidation state of all the lanthanoids) are of the
form 4f 
n (n = 1 to 14 with increasing atomic number)