Explain the following observations:
i) There is generally an increase in the density of elements from titanium (Z = 22) to copper (Z = 29) in the first series of transition elements.
ii) Transition elements and their compounds are generally found to be good catalysts in chemical reactions.
i) There is generally an increase in the density of elements from titanium (Z = 22) to copper (Z = 29) in the first series of transition elements.
ii) Transition elements and their compounds are generally found to be good catalysts in chemical reactions.
Solution
(i) From Ti to Cu the atomic mass keeps increasing while the atomic radius remains almost unchanged (slightly decreasing). Density = mass/volume, so the density rises steadily (Ti 4.5 → Cu 8.9 g cm).
(ii) Transition metals catalyse because (a) their variable oxidation states let them form unstable intermediate compounds, offering a path of lower activation energy, and (b) their surfaces adsorb reactant molecules (using vacant d-orbitals), increasing their local concentration and weakening their bonds — e.g. Fe in NH synthesis, VO in the contact process.
(ii) Transition metals catalyse because (a) their variable oxidation states let them form unstable intermediate compounds, offering a path of lower activation energy, and (b) their surfaces adsorb reactant molecules (using vacant d-orbitals), increasing their local concentration and weakening their bonds — e.g. Fe in NH synthesis, VO in the contact process.
CBSE Class 12 Board · 2010 · Delhi · Subjective