The d- and f-Block Elements

The d-block elements occupy groups 3 to 12 of the periodic table, with their d orbitals progressively filled, while the f-block elements, the lanthanoids and actinoids, fill the 4f and 5f orbitals. In this chapter you will study the position and electronic configurations of transition elements, including the exceptional configurations of chromium (3d5 4s1) and copper (3d10 4s1), and trends in their general properties: metallic character, atomic and ionic radii, ionisation enthalpies, variable oxidation states, standard electrode potentials, magnetic behaviour calculated by the spin-only formula, formation of coloured ions and complexes, catalytic activity, interstitial compounds and alloys. You will then learn the preparation and properties of two important compounds, potassium dichromate, prepared from chromite ore, and potassium permanganate, prepared from pyrolusite, including their oxidising reactions in acidic medium and the chromate-dichromate equilibrium. Finally, the chapter covers the lanthanoids, their oxidation states, the lanthanoid contraction and its consequences, the actinoids and their comparison with lanthanoids, and some applications of d- and f-block elements such as catalysts and mischmetall.

Detailed Worksheet: The d- and f-Block Elements Section A - Definitions (10 marks) 1. Define transition elements. Why are Zn, Cd and Hg not regarded as transition elements? (2 marks) 2. What is lanthanoid contraction? State two of its consequences. (2 marks) 3. What are interstitial compounds? State two of their characteristic properties. (2 marks) 4. Why do transition metals show variable oxidation states? Give the range of oxidation states of manganese. (2 marks) 5. What is mischmetall? State one use. (2 marks) Section B - Calculations and Applications (15 marks) 6. Calculate the spin-only magnetic moments of Ti3+, Cr3+, Mn2+ and Cu2+ ions (atomic numbers Ti 22, Cr 24, Mn 25, Cu 29; sqrt(3) = 1.73, sqrt(15) = 3.87, sqrt(35) = 5.92). (3 marks) 7. Calculate the volume of 0.02 M KMnO4 required to oxidise 25 mL of 0.1 M FeSO4 solution in acidic medium. Write the balanced ionic equation. (3 marks) 8. Calculate the mass of K2Cr2O7 (molar mass 294) required to oxidise 0.03 mol of Fe2+ ions to Fe3+ in acidic medium. Write the balanced ionic equation. (3 marks) 9. 25 mL of 0.05 M oxalic acid is titrated against KMnO4 in acidic medium. Write the balanced equation and calculate the volume of 0.01 M KMnO4 required. Why is the titration self-indicating? (3 marks) 10. Write the electronic configurations of Cr, Cu, Fe2+, Fe3+, Mn2+ and Zn2+. Use them to explain why Fe3+ is more stable than Fe2+, and why Zn2+ salts are colourless. (3 marks) Section C - Diagrams (10 marks) 11. Draw a graph showing the trend in melting points of the transition elements of the 3d series, and explain the maxima near the middle of the series. (4 marks) 12. Draw the structures of the chromate ion and the dichromate ion, and show the equilibrium between them with the effect of pH. (3 marks) 13. Draw the structures of the manganate and permanganate ions and a flowchart for the preparation of KMnO4 from pyrolusite. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Explain why the E0 value for Mn3+/Mn2+ (+1.57 V) is much more positive than that for Cr3+/Cr2+ (-0.41 V) or Fe3+/Fe2+ (+0.77 V). Explain why copper has a positive E0(M2+/M) value (+0.34 V) unlike other 3d metals. (5 marks) 15. Describe the preparation of potassium dichromate from chromite ore, giving all equations. Write the ionic equations for its oxidising action on (i) iodide (ii) iron(II) (iii) hydrogen sulphide in acidic medium. (5 marks) 16. Compare the lanthanoids and actinoids on the basis of electronic configuration, oxidation states, atomic and ionic sizes, and chemical reactivity. Explain why actinoid contraction is greater than lanthanoid contraction. (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Write balanced chemical and ionic equations, and use the data given for calculations.