Quick Recap — Reasons Behind the Trends

  • Coloured ions: d-d transitions absorb visible light; variable oxidation states: close (n−1)d(n-1)d/nsns energies.
  • High enthalpy of atomisation (strong metallic bonding from unpaired d-electrons) gives high melting points; Zn (d10^{10}) has a low melting point.
  • Catalysis: variable oxidation states + surface adsorption; alloys/interstitial compounds from similar atomic sizes and small interstitial atoms.
  • Lanthanoid contraction governs the near-identical chemistry of the heavier congeners.