Transition metals -5

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  • Created by: Shannon
  • Created on: 02-03-15 10:37
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  • Transition Metals
    • Defintion
      • An element which forms one or more ions with a partially filled d-orbital
        • Exceptions
          • Sc and Zn are not transition metals. This is because they form ions with either no electrons the d-orbital or full d-orbital
    • Properties
      • 1) They have many oxidation states - therefore can form many ions
      • 2) They form coloured ions
      • 3) They can form complex ions
      • 4) They have the ability to act as catalysts
    • Electron configurations
      • '4s first rule' - the 4s orbital is the first to fill with electrons and therefore the first to empty of electrons
        • Exceptions
          • Cr and Cu have half filled 4s orbitals
            • The resulting configuration is the most stable
              • Energy needed to promote the electron vs inter-electron repulsion
            • d-orbitals are more compact, therefore increased repulsions between electrons. d-orbitals less stable
              • 4s higher in energy, but difficult to promote electron
      • The highest oxidation state of any transition metal will be the oxidation state that gives it an electron config the same as Ar
      • e.g Co = [Ar] 3d74s2
    • Complexes
      • Ligands
        • Donate 2 electrons to form a dative covalent bond
          • Ligands can bond with 1 or more 'teeth'
            • Unidentate
            • Bidentate
            • Multidentate
      • Why do they form coloured complexes?
        • d-orbitals are degenerate, but when a ligand approaches, the orbitals are either destabilised or stabilised
          • A.K.A ligand field splitting
          • Tetrahedral complexes
            • Splitting occurs 3 up, 2 down
          • Octahedral complexes
            • Splitting occurs 2 up, 3 down
          • When visible light shines on the transition metal, electrons can be promoted from a low energy to higher
        • The colour we observe is the wavelength of light not absorbed
          • White light - wavelength absorbed
      • What is a complex?
        • Transition metal surrounded by ligands
    • Ionisation energy
      • 1st ionisation energy
        • The energy needed to remov 1 electron from a mole of gaseous atoms
        • No anomalies as 1st electron is always removed from the 4 s orbital
      • 2nd ionisation energy
        • Cr -> Mn & Cu -> Zn
          • Cr - electron  removed from 3d orbital = more energy needed to promote
          • Mn - electron removed from 4s shell = higher in energy, less energy needed to promote
      • 3rd ionisation energy
        • Mn -> Fe
          • Mn - Singly paired electrons = more stable
          • Fe - inter repulsion between electrons = less energy to remove electron as destabilised
    • Catalysis
      • Variable oxidation states make them good catalysts
      • Types
        • Heterogeneous
          • Catalyst in different phase to reactants
            • E.g solid catalyst with gaseous reactant particles - Fe in Haber process
        • Homogeneous
          • Catalyst in same phase as reactants
            • E.g

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