COLOURED IONS

• WHY ARE TRANSITION METALS COLOURED?

  • part filled d-orbitals
  • so electrons can move from one d-orbital to another
  • when electrons move to a higher energy d-orbital (excited) they absorb energy in the visible region of the spectrum equal to the difference in energy between levels
  • see a mixture of colours that are not absorbed
• FACTORS AFFECTING COLOUR?

  • metal
  • oxidation state
  • ligands
  • co-ordination number
• COLORIMETRY?

  • use light source and detector
  • to measure amount of light of a particular wavelength passing through a coloured solution
  • more concentrated solutions mean less light transmitted through
  • calibration curve
  • ligands used to intensify colour
• WHICH D-BLOCK ELEMENTS ARE NOT COLOURED AND WHY?

  Zn (2+), Cu (+), Sc (3+)

  • white as solids
  • colourless in solution
  • d-subshells are either empty or full
  • so electrons cannot be promoted from lower to higher d-orbitals
• WHAT CAN ALTER THE COLOUR OF A TRANSITION METAL?

  • if the compound is solid or in aqueous solution
  • concentration in solution
  • if there is any dissolved oxygen
• REDUCTION OF VANADIUM?

  • ammonium vanadate (V) in acidic conditions (hydrochloric/ sulfuric acid) using zinc as a reducing agent
  • V (+5) in VO2 (+) is yellow
  • V (+4) in VO (2+) is blue
  • V (+3) in V (3+) is green
  • V (+2) in V (2+) is violet