transition metals

• Transition metal characteristics


  Arise from an incomplete d sub-level in ions
• Zn is not a transition metal because Zn^2+ has a complete d orbital
• Sc is not a transition metal because Sc^3+ has an empty d orbital
• Complex


  A central metal ion surrounded by ligands
• Ligand


  An atom, ion or molecule which can donate a lone electron pair
• Coordinate bonding


  The shared pair of electrons in the covalent bond come from only one of the bonding atoms
• Coordination number


  The number of coordinate bonds formed to a central metal ion
• Transition metals commonly form octahedral complexes with small ligands and tetrahedral complexes with larger ligands
• Transition metals commonly form square planar complexes
• Ag+ commonly forms linear complexes
• Cis-trans isomerism


  Stereoisomerism in complex ions where two identical ligands are either adjacent (cis) or opposite (trans)
• Optical isomerism


  Stereoisomerism in complex ions where the complex and its mirror image are non-superimposable
• Cisplatin is used as an anticancer drug because it can bind to and disrupt DNA in cancer cells
• Ligand substitution reaction


  1. Replacement of one ligand by another in a complex ion

  2. Occurs when excess NH3 is added to aqueous transition metal ions

  3. Occurs when high concentration of Cl- is added to aqueous transition metal ions
• Fe(II) in haemoglobin enables oxygen transport in the blood
• Haem is an iron(II) complex with a multidentate ligand
• Reactions with Chloride ions


  1. Addition of a high concentration of chloride ions (from conc HCl or saturated NaCl) to an aqueous ion

  2. Ligand substitution reaction

  3. Cl- ligand is larger than the uncharged H2O and NH3 ligands so therefore ligand exchange can involve a change of co-ordination number
• If solid copper chloride (or any other metal) is dissolved in water it forms the aqueous [Cu(H2O)6]2+ complex and not the chloride [CuCl4]2- complex
• Haemoglobin


  Fe(II) in haemoglobin enables oxygen to be transported in the blood. Haem is an iron(II) complex with a multidentate ligand. O2 bonds to Fe2+ ions in the haemoglobin and when required the O2 is released.
• CO is toxic to humans as CO can from a strong coordinate bond with haemoglobin. This is a stronger bond than that made with oxygen and so it prevents the oxygen attaching to the haemoglobin. With CO, the stability constant is greater than with complex in O2.
• Precipitation reactions with sodium hydroxide and ammonia

  1. OH- and ammonia when in limited amounts form the same hydroxide precipitates

  2. [Cu(H2O)6]2+ + 2OH- Cu(H2O)4(OH)2 (s) + 2H2O

  3. [Mn(H2O)6]2+ + 2OH- Mn(H2O)4(OH)2 (s) + 2H2O

  4. [Fe(H2O)6]3+ + 3OH- Fe(H2O)3(OH)3 (s) + 3H2O

  5. [Fe(H2O)6]2+ + 2OH- Fe(H2O)4(OH)2 (s) + 2H2O
• Hydroxide precipitates


  • Cu(OH)2
  • Mn(OH)2
  • Fe(OH)2
  • Fe(OH)3
• Amphoteric


  Cr hydroxide can react with alkali to give a solution and react with acid to form the aqueous salt
• The Fe2+ and Cr2O7 2- in acid solution reaction can be used as a quantitative redox titration. This does not need an indicator
• When transition metals in low oxidation states are in alkaline solution


  They are more easily oxidised than when in acidic solution
• Transition elements show variable oxidation states