3.2.5 Transition metals

Cards (64)

  • Complex: central metal atom / ion surrounded by ligands
  • Ligand: A species which can use its lone pair to form a dative covalent bond to a transition metal.
  • Co-ordination number: Number of co-ordinate bonds to the central metal atom/ion
  • What shape is formed with a co-ordination number of 6? 
    • Octahedral
    • Small ligands e.g H2O and NH3
  • What types of ligands are there?

    • monodentate = attach with 1 co-ordinate
    • bondbidentate = attach with 2 co-ordinate bonds from two atoms (each donate lone pair)
    • multidentate = attach with multiple co-ordiinate bonds
  • What type of isomerism do square planar complexes display? Geometric isomerism
  • How can transition metals be identified? by their colour
  • Which acid do you use for redox if you want to reduce a species? HCl provides H+ for reduction
  • Acid to use for redox if you want to oxidise a species:
    • Use H2SO4 to provide H+ for oxidation
  • What is the effect of pH on redox in transition metals? Reduction favoured by acidic conditions
  • Bidentate ligand: Coordinate bonds from two atoms
  • Transition metals and their compounds can act as hetereogenous and homogenous catalysts
  • V2O5 and Fe are examples of heterogenous catalysts
  • Catalyst poisoning:
    • Impurities can block active sites
    • so the have reduced efficiency
  • What can act as a poison in the Haber process? sulphur
  • What can act as a poison in a catalytic converter? Lead
  • Haem: An iron (II) complex with a multidentate ligand. 
  • CO is toxic because it replaces O2 co-ordinately bonded to Fe (II) in haemoglobin.

    This prevents Hb from transporting O2
  • Chelate effect: Bidentate and multidentate ligands replace monodentate ligands from complexes - resulting in a more stable complex. 
  • W is a bad catalyst because it's adsorption is too strong
  • Ag is a a bad catalyst because

    adsorbtion is too weak and reactants do not absorb in high enough concentrations
  • Transition element: An element which forms at least one stable ion with a partially full d-shell of electrons
  • Where are the transition metals located in the periodic table? In the middle (block from Ti to Cu) - part of the d-block
  • What are some characteristic physical properties of transition metals?
    • Metallic
    • good conductors of heat and electricity
    • hard, strong, shiny
    • high m.p., high b.p., low reactivity.
  • What are the characteristic chemical properties of transition metals:
    • Variable oxidation states → take part in many redox reactions
    • Coloured compounds/ions in solution
    • Good catalysts
    • Form complex ions
  • Catalysts are usually spread over an inert support medium to
    • Increase surface area
    • Reduce cost
  • Which electrons do transition metals lose first when forming ions? 4s
  • mono/unidentate ligands: A ligand that forms one co-ordinate bond to the central metal ion (one lone pair to donate)
  • Give some examples of common monodentate ligands: Cl- , H2O, NH3 , CN
  • How many co-ordinate bonds does EDTA4- form? six
  • Define the term coordination number: The number of co-ordinate bonds the metal ion has formed to surrounding ligands
  • Chelate effect: Chelate complexes with multidentate ligands are favoured over monodentate ligands or ligands that form fewer co-ordinate bonds per molecule
  • If a transition metal ion has 2 ligands, what shape is it usually? Linear
  • If a transition metal ion has 4 ligands, what shape is it usually? Tetrahedral
  • What shape is a complex ion if it has 6 ligands? Octahedral
  • What conditions are needed for a complex ion display to optical isomerism? Usually applies to octahedral molecules with 2 or more bidentate ligands, so that the mirror images are non-superimposable
  • What affects the colour of a transition metal compound?
    • ΔE affects the frequency of absorbed photons, so determines the colour
    • ΔE is changed by oxidation state of the metal, number and type of ligands, shape, co-ordination number
  • What colour is Fe2+’s aqua ion? Green
  • What colour is Fe3+’s aqua ion? Pale brown
  • What colour is Cr2+’s aqua ion? blue