transition metals

• Transition metals


  Elements with an incomplete d sub-level in atoms or ions
• Transition metal elements


  • Sc
  • Ti
  • V
  • Cr
  • Mn
  • Fe
  • Co
  • Ni
  • Cu
  • Zn
• Transition metal ions


  • Sc 3+
  • Ti 3+
  • V 3+
  • Cr 3+
  • Mn 2+
  • Fe 3+
  • Co 2+
  • Ni 2+
  • Cu 2+
  • Zn 2+
• 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-
• Multidentate ligands


  • EDTA4-
• Ligand substitution reaction


  1. Ligand exchange

  2. Coordination number change
• Ligand substitution reactions


  • [Co(H2O)6]2+ + 6NH3 → [Co(NH3)6]2+ + 6H2O

  [Cu(H2O)6]2+ + 4NH3 → [Cu(NH3)4(H2O)2]2+ + 4H2O

  [Cu(H2O)6]2+ + 4Cl- → [CuCl4]2- + 6H2O

  [Fe(H2O)6]3+ + 4Cl- → [FeCl4]- + 6H2O
• Dissolving solid copper chloride in water forms [Cu(H2O)6]2+ not [CuCl4]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 ligands with bidentate or multidentate ligands leads to a more stable complex
• The chelate effect is due to a positive entropy change as there are more moles of products than reactants
• EDTA complexes are stable and have many applications
• EDTA titrations


  Find moles of EDTA

  2. Use 1:1 ratio to find moles of metal ion

  3. Calculate concentration of metal ion
• Shapes of complex ions

  • Octahedral

  Tetrahedral

  Square planar

  Linear
• Examples of complex ion shapes


  • [Co(NH3)6]2+

  [Cu(H2O)6]2+

  [CoCl4]2-

  [Ag(NH3)2]+
• Cis-trans isomerism


  Stereoisomerism in square planar and octahedral complexes
• Examples of cis-trans isomers

  • cis-[Cr(H2O)4Cl2]+

  trans-[Ni(NH3)2Cl2]
• Optical isomerism


  Stereoisomerism in octahedral complexes with 3 bidentate ligands
• Examples of optical isomers


  • [Ni(NH2CH2CH2NH2)3]2+
• Colour in complexes


  Arises from electronic transitions between d orbitals
• Factors affecting colour


  Oxidation state

  Coordination number

  Ligand
• Compounds without d electrons or with full d shells are colourless
• Equations for colour


  ΔE = hv

  ΔE = hc/λ
• d block


  Member of the d block
• Sc3+


  Ion has no d electrons left to move around, so no energy transfer equal to visible light
• Zn2+ and Cu+ ions

  d shell is full (3d10), so no space for electrons to transfer, no energy transfer equal to visible light
• In the equation O2, only the oxidation state is changing
• [Co(H2O)6]2+ + 6 NH3

  1. Produces [Co(NH3)6]2+ + 6H2O

  2. Changes ligand and coordination number
• Equation


  Changes only the ligand
• How colour arises


  Equations link colour, wavelength, frequency of absorbed light, and energy difference between split d orbitals
• v


  Frequency of light absorbed (unit s-1 or Hz)
• h


  Planck's constant 6.63 × 10–34 (J s)