d-orbital

Oxidation States of d-Block Elements: d-block elements exhibit variable oxidation states due to the involvement of (n-1)d and ns electrons in bonding.

Important Oxidation States and Colors:

• Cr: +3 (violet/green), CrO42− (yellow), Cr2O72− (orange)

• Mn: +2, +4, +7, MnO4− (purple)

• Fe: +2 (pale green), +3 (yellow/brown)

• Co: +2 (pink)

• Cu: +2 (blue)

Bonding in Complexes:

• Tetrahedral and octahedral complexes involve coordinate bonds between metal ions and ligands.

Origin of Color in Transition Metal Complexes:

• Color arises from d-d transitions, influenced by crystal field splitting (e.g., [Cu(H2O)6]^{2+} and [Fe(H2O)6]^{3+}).

Ligand Exchange and Coordination Number:

• Ligand exchange can alter coordination number (e.g., reactions of [Cu(H2O)6]^{2+} and [Co(H2O)6]^{2+} with concentrated HCl).

Colors and Formulae of Complex Ions:

• Octahedral: [Cu(H2O)6]^{2+} (blue), [Cu(NH3)4(H2O)2]^{2+} (deep blue), [Co(H2O)6]^{2+} (pink)

• Tetrahedral: [CuCl4]^{2−} (yellow/green), [CoCl4]^{2−} (blue)

Catalytic Properties:

• Transition metals exhibit catalytic properties; heterogeneous catalysis involves surface adsorption, while homogeneous catalysis involves variable oxidation states.

Catalysts in Industrial Processes:

• Ni (hydrogenation of alkenes), Fe (Haber process).

Examples of Catalysis:

• V2O5 (contact process), MnO2 (decomposition of H2O2).

Reactions with Excess Aqueous OH-:

• Cr^{3+}: green precipitate of Cr(OH)3

• Fe^{2+}: green precipitate of Fe(OH)2

• Fe^{3+}: brown precipitate of Fe(OH)3

• Cu^{2+}: blue precipitate of Cu(OH)2