transition metals

• transition metals = metals which form stable ions with partially fillled d orbitals
• properties of transition metals:

  • variable oxidation states
  • catalysts
  • form coloured compounds
• ligand is a molecule/ion that forms a coordinate bond with a transition metal by donating a pair of electrons e.g h20 and nh3
• a ligand can be a molecule or an ion
• coordination number = number of coordinate bonds
• size of ligand determines coordination number - if ligand is big there will be less of them
• ligands surrounding metal ions are known as complex ions
• square brackets used to show charge
• if complex ions contain 2 ligands they are named in alphabetical order eg in cisplatin ammonia comes before chloride
• a metal ion in a complex with a negative charge ends in ate:

  • cobalt = cobaltate
  • chromium = chromate
  • copper = cuprate
  • iron = ferate
• 6 ligands = octahedral
• 4 ligands = tetrahedral

  example = cocl4
• 2 ligands = linear

  example = tollens reagent
• nickel paladium and platinum tend to be square planar for eg cisplatin
• CIS = 2 identical ligands next to each other

  trans = 2 identical ligands opposite each other
• example of multidentate ligand = EDTA 4-
• when light is absorbed d elctrons move from ground state to excited state to a higher energy level
• difference in energy levels is = frequency of light absorbed
• change in energy = planks constant x frequency

  frequency in hz
• change in energy = planks constant x speed of light / wavelegnth

  wavelegnth in metres
• higher oxidation state = more d orbital splitting = higher frequencies of light absorbed
• ammonia ligands cause more d orbital splitting than water ligands
• order of splitting highest to lowest:

  • nh3
  • h20
  • oh-
  • f-
  • cl-
• higher coordination number = more d orbital splitting = higher frequency of light absorbed = closer to blue end of visible spectrum
• 3 factors affecting colour of complex ions:

  • coordination number
  • oxidation state
  • type of ligand
• colorimetry - used to find unknown concentration
• colorimetry:

  • first measure the absorbtion of the colour you are working out the concentration of - by shining its complimentary colour through and using a detector
  • produce calibration curve:
  • plot a graph with know concentrations - absorbance on y axis and concentration on x axis
  • draw line of best fit
  • then read off the concentration at the asorbance of your sample
• nm to m = x10^-9
• thz to hz = x10^12
• why is colorimetry preferred to titration:

  • allows for quick measurements
  • dosent require use of indicator
  • not subjective - in terms of colour change
• Why are transition metal ions coloured

  • Absorb some frequencies of visible light
  • To excite elctrons in d orbitals
  • Remaining frequencies / complementary colours reflected
• ligand substitution reaction is when one ligand replaces another
• why might enthalpy change be close to 0


  same number of bonds breaking and bonds forming
• lowry base = ligand substitution reaction