How would you account for the following?
i) The transition elements have high enthalpies of atomisation.
ii) The transition metals and their compounds are found to be good catalysts in many processes.
i) The transition elements have high enthalpies of atomisation.
ii) The transition metals and their compounds are found to be good catalysts in many processes.
Solution
(i) In transition metals the unpaired (n−1)d electrons as well as the ns electrons take part in metallic bonding. The large number of bonding electrons makes interatomic forces very strong, so a great deal of energy is needed to pull atoms out of the metal — high enthalpies of atomisation.
(ii) Their catalytic power rests on (a) variable oxidation states, letting them form and decompose intermediate compounds that provide a lower-energy path, and (b) their ability to adsorb reactants on the metal surface (vacant d-orbitals), concentrating them and loosening their bonds — e.g. Fe (Haber), Ni (hydrogenation), VO (contact process).
(ii) Their catalytic power rests on (a) variable oxidation states, letting them form and decompose intermediate compounds that provide a lower-energy path, and (b) their ability to adsorb reactants on the metal surface (vacant d-orbitals), concentrating them and loosening their bonds — e.g. Fe (Haber), Ni (hydrogenation), VO (contact process).
CBSE Class 12 Board · 2007 · All India · Subjective