What is Lanthanoid contraction ?

(a) What is Lanthanoids contraction ? (b) What are Interstial compounds ? Give one example (c) Calculate the spin only magnetic moment of M^(2+)(aq) ion [Z=29].

(a) How would you account for the following : (i) Cobalt (II) is stable in aqueous solution but in the presence of strong ligands, it is easily oxidised. (ii) The transition metals form interstitial compounds. (iii) Silver halides find use in photography. (b) What is lanthanoid contraction ? Mention its main consequences.

(i) Which is the last element in the series of the actinoids? Write the electronic configuration of this element. Comment on the possible oxidation state of this element. (ii) What is lanthanoid contraction? Name an important alloy which contains some of the lanthanoid metals.

Lanthanoid contraction implies