Transition metals

    Cards (102)

    • 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
    • Types of ligands
      • Monodentate (e.g. H2O, NH3, Cl-)
      • Bidentate (e.g. NH2CH2CH2NH2, C2O4 2-)
      • Multidentate (e.g. 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
    • Chelate effect
      The substitution of monodentate ligands with bidentate or multidentate ligands leads to a more stable complex
    • Chelate effect
      Increases entropy, small enthalpy change, negative free energy change
    • EDTA titrations
      1. Form stable 1:1 metal-EDTA complex
      2. Quantitative analysis of metal ions
    • Complex ion shapes
      • Octahedral
      • Tetrahedral
      • Square planar
      • Linear
    • Types of isomerism in complex ions
      • Cis-trans isomerism
      • Optical isomerism
    • Colour in complex ions
      Arises from electronic transitions between d orbitals
    • Changing ligand or coordination number
      Changes the energy splitting between d orbitals, changing the frequency of light absorbed
    • Compounds without colour: Sc3+, Zn2+, Cu+ have full d orbitals
    • d block
      Transition metals
    • Sc3+
      Ion with 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 with energy difference between split d orbitals
    • v
      Frequency of light absorbed (s-1 or Hz)
    • h
      Planck's constant 6.63 × 10–34 (J s)
    • E
      Energy difference between split orbitals (J)
    • c
      Speed of light 3.00 x 108 (m s–1)
    • λ
      Wavelength of light absorbed (m)
    • A solution will appear blue if it absorbs orange light. The energy split in the d orbitals ΔE will be equal to the frequency of orange light(5 x1014 s-1) x Planck's constant
    • ΔE in a blue solution = hv = 6.63 × 10–34 x 5 x1014 = 3.32 × 10–19 J
    • Octahedral complex ion

      • Average energy of d orbitals in field of ligands
    • Absorption of visible light in spectrometry
      1. Add appropriate ligand to intensify colour
      2. Make up solutions of known concentration
      3. Measure absorption or transmission
      4. Plot graph of absorption vs concentration
      5. Measure absorption of unknown and compare
    • The amount of light absorbed is proportional to the concentration of the absorbing species (and to the distance travelled through the solution)
    • Some complexes have only pale colours and do not absorb light strongly. In these cases a suitable ligand is added to intensify the colour
    • Spectrometers
      Contain a coloured filter to allow wavelengths of light through that would be most strongly absorbed by the coloured solution
    • Transition elements
      • Show variable oxidation states
      • Lose 4s electrons before 3d when forming ions