Introduction to D and F Blocks

Overview

This lecture focuses on D and F block elements, discussing their characteristics, electronic structure, oxidation states, and important compounds.

D Block Elements

• In the D block, the last electron enters the d sub-shell; these are also called transition elements.
• Transition elements: those whose d orbitals are partially filled (d¹-d⁹).
• Zn, Cd, Hg (d¹⁰) are not transition elements.
• Typical electronic configuration is (n-1)d¹⁻¹⁰ns¹⁻², with some exceptions (like Cr, Cu, Pd).
• Size decreases from left to right; ionization energy generally increases.
• Alloy formation is due to small size differences.
• Interstitial compounds are formed by trapping small atoms in voids.
• D-block elements show various oxidation states; Mn can go from +2 to +7.
• Most ions of the D block are colored (d⁰ and d¹⁰ are colorless).
• Variable oxidation states and ability to form complexes; higher complex tendency due to small size and high charge.

Important Compounds of d-Block (KMnO₄, K₂Cr₂O₇)

• KMnO₄ is a strong oxidizer, works in both acidic and basic media.
• Color in MnO₄⁻ is due to charge transfer.
• K₂Cr₂O₇ is orange and chromate ion is yellow; they are interconvertible depending on pH.
• Both have tetrahedral structures; bond order or length is determined by resonance.

F Block Elements (Lanthanides and Actinides)

• Lanthanides are most stable in +3 oxidation state; some show +2 or +4.
• Size decreases from left to right due to lanthanide contraction.
• Electrons mainly fill 4f orbitals, with some exceptions in d.
• All are silvery white and tarnish quickly in air.
• Actinides are all radioactive; show oxidation states other than +3.
• Actinide contraction is stronger than lanthanide contraction due to poor shielding of 5f electrons.
• They are highly reactive and undergo surface oxidation (passivation) with concentrated HNO₃.

Key Terms & Definitions

• Transition Elements — those with partially filled d orbitals.
• Interstitial Compounds — small atoms trapped in voids of D block metals.
• Lanthanide Contraction — size reduction due to poor shielding by 4f electrons.
• Oxidation State — number of electrons lost or gained by an atom.
• Complex Compound — metal ion surrounded by ligands.
• Charge Transfer — movement of electrons from ligand to metal or metal to ligand.

Action Items / Next Steps

• Study the D and F block chapters from NCERT.
• Review electronic configurations of lanthanides and actinides.
• Revise preparation and reactions of key compounds (KMnO₄, K₂Cr₂O₇).