Question

Give reasons for the following: 

(a) Transition elements and their compounds act as catalysts. 

(b) E° value for (Mn²⁺ |Mn) is negative whereas for (Cu²⁺ |Cu) is positive. 

(c) Actinoids show irregularities in their electronic configuration.

Answer 1

(a) The catalytic properties of transition metals are attributed to their ability to exist in multiple oxidation states and form complexes. Variable oxidation states make them more efficient catalysts.

(b) The electronic configuration of Mn²⁺ is d⁵ which is more stable because of half-filled d-subshell. While Cu²⁺ with electronic configuration d⁹ becomes stable after accepting two electrons with configuration d¹⁰ s¹ due to fully-filled d-orbital.

(c) The elements Th (At. no. 90) to Lr (At. no. 103) are together known as actinoids. For the first four actinoids Th, Pa, U and Np, the difference between the energy levels of 5f and 6d orbitals is small. Thus, in these elements (or ions) electrons may occupy either 5d or 6f orbitals.