Transition metals

• Transition metal

  Transition elements are located in the d-block of the periodic table
• Transition elements


  • They contain partially filled d-orbitals
  • They have similar physical properties and different chemical properties
  • They form complexes
  • They form coloured compounds in solutions
  • They have variable oxidation states
  • They are good catalysts
• Transition elements have variable oxidation states because the 4s and 3d orbitals are very close in energy
• This makes it easy to lose electrons from both orbitals and also allows the remaining electrons to form stable configurations
• Copper and chromium are exceptions to the rule that the 4s subshell is filled before the 3d subshell
• Chromium electron configuration


  It is more stable if one of the electrons from the 4s orbital is instead in the 3d orbital, so that each 3d orbital contains one unpaired electron
• Copper electron configuration


  It is more stable if the 3d sub-shell is completely filled, so one of the 4s electrons is moved to form [Ar]3d^10 4s^1
• Transition metal complexes


  Consist of a central metal ion surrounded by ligands
• Common ligands


  • H2O
  • NH3
  • Cl-
• Monodentate ligands


  Share/form one dative bond
• Bidentate ligands


  Share/form 2 dative bonds
• Hexadentate ligands


  Form 6 dative bonds
• Coordination number


  The total number of coordinate bonds formed with a central metal ion
• Transition metals can be identified by their colour, which changes depending on the coordination number of the complex, the type of ligand bonded to the ion, and the oxidation state
• Colour arises


  When white light shines on a substance, some wavelengths are absorbed but the remaining wavelengths are reflected and transmitted to the human eye. The reflected wavelengths correspond to a specific colour which is then observed.
• In transition metal complexes, ligands cause the d-orbitals to split, meaning some electrons exist in slightly higher energy levels
• Some metal ions and complexes are colourless because they do not contain partially filled d-orbitals, so there are no available electrons to excite and move around</b>
• Octahedral complexes


  • Transition metal complexes with H2O and NH3 ligands commonly form octahedral complexes with a bond angle of 90°
  • Octahedral complexes are formed when there is six-fold coordination with monodentate ligands
• Tetrahedral complexes


  • When complexes form with larger ligands such as Cl-, they form tetrahedral complexes with a bond angle of 108.8°
  • Tetrahedral complexes can show optical isomerism
• Square planar complexes


  • Platinum and nickel complexes form in a square planar shape, consisting of four coordinate bonds with a bond angle of 90°
• Cisplatin is the cis isomer of a square planar complex of platinum, and is commonly used as a cancer therapy drug
• Drugs like cisplatin target components of cells that are chiral, so only the single enantiomer will work and cure the disease
• Cisplatin can cause serious side effects such as hair loss, so it has to be administered in small amounts to try and reduce the effects
• Ligand substitution


  Ligands in a transition metal complex can be exchanged for other ligands
• When the oxygen usually bound to haem is replaced with carbon monoxide


  Carbon monoxide is toxic to humans as it prevents oxygen from being transported around the body
• Vanadium oxidation states


  Vanadium has four possible oxidation states from +5 to +2, each of which produces a different coloured compound
• Vanadium oxidation states


  • +5 (yellow), +4 (blue-green), +3 (blue), +2 (green)
• Vanadium can be reduced from an oxidation state of +5 all the way to +2 via reduction with zinc in acidic conditions
• Reduction potential (E°)


  The more positive the reduction potential, the more favourable the reduction reaction
• As the oxidation state of vanadium decreases, the reduction potential becomes less positive, to the point where the reduction of V2+ to V is less favourable than the oxidation of V2+ to V3+
• pH effect on oxidation/reduction

  • Acidic conditions are required for ions to be reduced (oxidation state becomes more negative)
  • Alkaline conditions are required for ions to be oxidised (oxidation state becomes more positive)
• Chromium oxidation states


  The most stable oxidation states are +6, +3 and +2
• Oxidation of Cr3+ to Cr6+

  1. Cr3+ can be oxidised to Cr6+ (chromate) by hydrogen peroxide in alkaline conditions

  2. The reaction first forms Cr3+ which is then converted to Cr2O7^2- by acidification
• Acidification of a solution containing Cr2O7^2- will cause the equilibrium to shift to the right, increasing the concentration of Cr2O7^2-
• Reactions of metal aqua ions with sodium hydroxide

  • Chromium: Violet solution, green precipitate
  • Iron: Yellow solution, brown precipitate
  • Cobalt: Pink solution, no precipitate
  • Copper: Blue solution, blue precipitate
• Reactions of metal aqua ions with ammonia

  • Chromium: Violet solution, no further reaction
  • Iron: Yellow solution, no further reaction
  • Cobalt: Pink solution, no precipitate
  • Copper: Blue solution, deep blue solution
• Metal aqua ions


  Chromium, iron, cobalt, copper
• Reactions of metal aqua ions

  1. React with sodium hydroxide to form coloured precipitates

  2. React with aqueous ammonia to form coloured solutions and precipitates
• Transition metal aqua ions and their reactions

  • Cr(H2O)6^3+ - Violet solution
  • Fe(H2O)6^2+ - Green solution, Green precipitate
  • Fe(H2O)6^3+ - Yellow solution, Brown precipitate
  • Co(H2O)6^2+ - Pink solution, Blue precipitate
  • Cu(H2O)6^2+ - Blue solution, Blue precipitate
• The number of OH- substituted is the same as the value of the charge on the initial ion