AQA Transition Metals Revision Guide

General Properties of Transition Metals

• Transition metals have incomplete d sub-levels in atoms or ions.
• Examples:
  • Sc: 1s²2s²2p⁶3s²3p⁶4s²3d¹
  • Ti: 1s²2s²2p⁶3s²3p⁶4s²3d²
  • Cu: 1s²2s²2p⁶3s²3p⁶4s¹3d¹⁰
• Ions lose 4s electrons before 3d.

Why Zinc is Not a Transition Metal

• Zinc forms a +2 ion with a complete d orbital.
• Exhibits complex formation, colored ions, variable oxidation states, and catalytic activity.

Complex Formation

• Complex: Central metal ion surrounded by ligands.
• Ligand: Atom, ion, or molecule donating a lone electron pair.
• Involves coordinate bonding; coordination number indicates the number of coordinate bonds.

Ligand Substitution Reactions

• Ligands:
  • Monodentate (e.g., H₂O, NH₃, Cl⁻)
  • Bidentate (e.g., NH₂CH₂CH₂NH₂)
  • Multidentate (e.g., EDTA⁴⁻)
• Coordination number may change with ligand exchange (e.g., Co²⁺, Cu²⁺).

Stability of Complexes

• Chelate effect: Stability increases with substitution of multidentate ligands due to entropy changes.
• EDTA complexes help in removing toxic metal ions and are used in shampoos for hard water.

Shapes of Complex Ions

• Octahedral complexes with small ligands.
• Tetrahedral complexes with larger ligands (e.g., Cl⁻).
• Square planar complexes (e.g., cisplatin).

Isomerism in Complex Ions

• Cis-trans isomerism in square planar and octahedral complexes.
• Optical isomerism with complexes having bidentate ligands.

Colour of Transition Metal Complexes

• Colour arises from d-d electronic transitions.
• Changing ligands/coordination number affects energy split between d orbitals.
• Absorption of visible light used in spectrophotometry for analyzing concentration.

Variable Oxidation States

• Transition metals lose 4s electrons first.
• Stability trends: +2 state more stable across period.
• High oxidation states are oxidizing agents (e.g., MnO₄⁻); low states are reducing agents (e.g., Fe²⁺).

Catalysis

Heterogeneous Catalysis

• Occurs at the surface of solid catalysts.
• Steps involve adsorption, bond weakening, product formation, and desorption.
• Surface area and strength of adsorption determine effectiveness.
• Examples: V₂O₅ in the Contact process, Fe in Haber process.

Homogeneous Catalysis

• Transition metals catalyze through variable oxidation states.
• Examples:
  • Reaction between iodide and persulfate ions.
  • Autocatalysis by Mn²⁺ in C₂O₄²⁻ and MnO₄⁻ titrations.

Silver Chemistry

• Silver forms complex ions similar to transition metals.
• Reactions of halides with AgNO₃:
  • Chlorides: white precipitate
  • Bromides: cream precipitate
  • Iodides: pale yellow precipitate
• Used in Tollens' reagent to distinguish aldehydes and ketones.

These notes cover the key aspects of transition metals, including their properties, complex formation, ligand substitution, stability, isomerism, color, variable oxidation states, and catalysis. Additionally, the chemistry of silver, particularly its role in forming complexes and reactions with halides, is discussed.