Transition Metals

• Transition metals


  Elements where the d sub-level in atoms or ions is incomplete
• Transition metal elements


  • Sc
  • Ti
  • V
  • Cr
  • Mn
  • Fe
  • Co
  • Ni
  • Cu
  • Zn
• Zinc is not a transition metal because Zn2+ has a complete d orbital
• Transition metal characteristics


  • Complex formation
  • Formation of coloured ions
  • Variable oxidation state
  • Catalytic activity
• 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
• Monodentate ligands


  • H2O
  • NH3
  • Cl-
• Bidentate ligands


  • NH2CH2CH2NH2
  • C2O4^2-
• Ligands can be monodentate, bidentate or multidentate
• Substitution reactions


  1. Ligand exchange

  2. Change in coordination number
• Addition of conc HCl to aqueous ions of Cu and Co

  Changes coordination number from 6 to 4
• Dissolving solid copper chloride in water forms [Cu(H2O)6]2+ complex, not [CuCl4]2-
• EDTA4- forms a 1:1 complex with metal(II) ions
• Bidentate ligands mentioned


  • NH2CH2CH2NH2
  • C2O4^2-
• Formation of bidentate complexes


  [Cu(H2O)6]2+ + 3NH2CH2CH2NH2 → [Cu(NH2CH2CH2NH2)3]2+ + 6H2O

  [Cu(H2O)6]2+ + 3C2O4^2- → [Cu(C2O4)3]4- + 6H2O
• Formation of multidentate complexes


  [Cu(H2O)6]2+ + EDTA4- → [Cu(EDTA)]2- + 6H2O
• Chelate effect


  The substitution of monodentate ligand with a bidentate or a multidentate ligand leads to a more stable complex
• The chelate effect can be explained by a positive entropy change
• EDTA titrations


  [Cu(H2O)6]2+ + EDTA4- → [Cu(EDTA)]2- + 6H2O
• EDTA complexes are stable and have many applications
• Octahedral shape


  Common for complexes with small ligands like H2O and NH3
• Tetrahedral shape


  Common for complexes with larger ligands like Cl-
• Square planar shape


  Formed by some transition metal complexes
• Linear shape


  Common for Ag+ complexes like [Ag(NH3)2]+
• Types of stereoisomerism in complex ions

  • Cis-trans isomerism
  • Optical isomerism
• Cis-trans isomers


  • cis-[Cr(H2O)4Cl2]+

  trans-[Cr(H2O)4Cl2]+

  cis-Ni(NH3)2Cl2

  trans-Ni(NH3)2Cl2
• Optical isomers


  • [Co(NH2CH2CH2NH2)3]2+
• Colour changes


  Arise from changes in oxidation state, coordination number or ligand
• Colour arises from electronic transitions between d orbitals
• Changing ligand or coordination number

  Alters the energy split between d orbitals, changing the frequency of light absorbed
• Compounds without d electrons or with full d shells are colourless
• Equations for colour


  ΔE = hv

  ΔE = hc/λ
• d block


  Transition metal
• Sc3+


  Transition metal ion with no d electrons left to move around
• Sc3+ ion has no energy transfer equal to that of visible light
• Zn2+ and Cu+ ions

  d shell is full (3d10), so there is no space for electrons to transfer
• Zn2+ and Cu+ ions have no energy transfer equal to that of visible light
• Oxidation state changing


  Only oxidation state is changing