Lanthanoids · Part 2

(as in ionisation enthalpies) arises mainly from the extra stability of empty, half-filled or filled f subshell. Thus, the formation of Ce IV is favoured by its noble gas configuration, but it is a strong oxidant reverting to the common + state. The E o value for Ce + / Ce + is + . V which suggests that it can oxidise water. However, the reaction rate is very slow and hence Ce(IV) is a good analytical reagent. Pr, Nd, Tb and Dy also exhibit + state but only in oxides, MO . Eu + is formed by losing the two s electrons and its f configuration accounts for the formation of this ion. However, Eu + is a strong reducing agent changing to the common + state. Similarly Yb + which has f configuration is a reductant. Tb IV has half-filled f -orbitals and is an oxidant. The behaviour of samarium is very much like europium, exhibiting both + and + oxidation states. . . Oxidation States Fig. . : Trends in ionic radii of lanthanoids Electronic configurations* Radii/pm Atomic Name Symbol Ln Ln Ln Ln + Ln Ln Number Lanthanum La 5d 6s 5d Cerium Ce 5d 6s Praseodymium Pr 6s Neodymium Nd 6s Promethium Pm 6s Samarium Sm 6s Europium Eu 6s Gadolinium Gd 5d 6s 5d Terbium Tb 6s Dysprosium Dy 6s Holmium Ho 6s Erbium Er 6s Thulium Tm 6s Ytterbium Yb 6s Lutetium Lu 5d 6s 5d Table . : Electronic Configurations and Radii of Lanthanum and Lanthanoids * Only electrons outside [Xe] core are indicated All the lanthanoids are silvery white soft metals and tarnish rapidly in air. The