Ch 8 covers d-block (transition) and f-block (lanthanoids, actinoids) elements — their electronic configurations, variable oxidation states, colour, magnetic properties, catalytic activity, and important compounds.
Transition metals: (n−1)d partially filled in ground state or common ions. Properties: variable oxidation states (due to comparable energies of ns and (n−1)d), coloured ions (d-d transitions), paramagnetic (unpaired electrons), form complexes, good catalysts. KMnO₄: strong oxidiser in acidic/basic media. K₂Cr₂O₇: orange in acidic, yellow (CrO₄²⁻) in basic.
Lanthanoids (4f filling): very similar properties, +3 common, lanthanoid contraction (decrease in size across series due to poor shielding of 4f). Actinoids (5f filling): radioactive, variable oxidation states (+3 to +7 for U), more size variation than lanthanoids.
Download: https://ncert.nic.in/textbook/pdf/lech108.pdf | Part I: https://ncert.nic.in/textbook/pdf/lech1ps.zip
Colour arises from d-d electronic transitions. When light falls on the compound, electrons jump from lower-energy d-orbitals to higher-energy ones (split by ligands). The absorbed wavelength's complementary colour is observed. Zn²⁺ (d¹⁰) and Sc³⁺ (d⁰) are colourless because no d-d transition is possible.
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