Transition metals

• A transition metal is a d-block element that can form at least one stable ion with a partially filled d-subshell
• Scandium and zinc are not transition elements because they don't form a stable ion with a partially filled d-subshell
• Properties


  Variable oxidation states

  Form coloured ions in solution

  Good catalysts
• Transition metals have variable oxidation states because the electrons sit in 4s and 3d energy levels which are very close

  As a result, electrons are gained and lost using a similar amount of energy when they form the ions
• V2+ is violet
• V3+ is green
• VO^2+ is blue
• VO2^+ is yellow
• Cr3+ is green/violet
• Cr2O72- is orange
• Mn2+ is pale pink
• MnO4- is purple
• Fe2+ is pale green
• Fe3+ is yellow
• Co2+ is pink
• Ni2+ is green
• Cu2+ is blue
• A transition metal complex is where a central transition metal ion is surrounded by ligands bonded by dative covalent bonds
• Ligands have at least 1 lone pair of electrons where they are used to form a dative covalent bond with the metal
• Monodentate ligands are ligands which only have one lone pair of electrons
• What are the examples of monodentate ligands?

  H2O:

  :NH3

  :Cl-
• Bidentate ligands are ligands which have 2 lone pairs of electrons
• What are the examples of bidentate ligands?

  Ethanedioate

  Ethane-1,2-diamine
• Multidentate ligands are ligands which have more than one coordinate bond
• EDTA4- is an example of a multidentate ligand
• The coordination number is the number of coordinate bonds in a complex
• Examples of small ligands are H2O and NH3, 6 can fit around a central metal ion
• Examples of larger ligands is Cl-, only 4 can fit around a central metal ion

  3 ethanedioate and ethane-1,2-diamine can fit around a central metal ion
• Complexes with a coordination number of 4 form tetrahedral and square planar shapes which have a bond angle of 109.5
• Pt[(NH3)2(CL)2] / cisplatin is an example of a square planar complex which has a bond angle of 90
• Complexes with a coordination number of 2 form linear shapes such as tollen's reagent which has a bond angle of 180
• Haem is multidentate ligand that is found in haemoglobin

  Haemoglobin is a protein used to transport oxygen around the body in the blood

  The structure is octahedral

  4 of the nitrogen's comes from one multidentate ligand called haem
• How does haemoglobin work?

  Oxygen substitutes the water ligand in the lungers where oxygen concentration is high to form oxyhaemoglobin, this is transported around the body

  Oxyhaemoglobin gives up oxygen to a place where it is needed

  Water takes the place and haemoglobin returns back to the lungs to start the process again
• Haemoglobin and carbon monoxide

  Carbon monoxide is a poisonous gas that causes headaches, unconsciousness and even death

  If carbon monoxide is inhaled, the water ligand is replaced with a carbon monoxide ligand

  Carbon monoxide binds strongly so is not readily replaced by oxygen or water

  This means that oxygen can't be transported and leads to oxygen starvation in organs
• D-orbital splitting


  The d-subshell is split into 2 when ligands bond with the central metal ion

  When electrons absorb light energy some move from the lowest energy level to higher energy level orbitals
• Calorimetry is used to determine the concentration of transition metal ions in solution

  1. Calorimeter must be set to zero by measuring the absorbance of a blank sample (solvent)
  2. White light filtered into narrow range of frequencies, monochromatic light is produced. Filter must be what is absorbed by the metal ion solution
  3. Monochromatic light passes through sample and some light is absorbed, sample held in a cuvette
  4. Light not absorbed travels to the detector, detector measures level of absorbance by comparing it to the absorbance in the blank sample
• We make samples by diluting different concentrations of the metal ion

  We must use the same metal ion and solvent as the one to be tested
• Vanadium chemistry


  Vanadium (V) VO2^+ can be reduced using zinc in an acidic solution all the way to V^2+

  1. VO2^+ is reduced to VO^2+ and there's a colour change of yellow to blue
  2. VO^2+ is reduced to V3+ and there's a colour change of blue to green
  3. V3+ is reduced to V2+ with a colour change of green to violet
• Contact process


  V2O5 oxidises SO2 to SO3 and is itself reduced to V2O4

  • V2O5 + SO2 --> V2O4 + SO3

  V2O5 is oxidised by oxygen to reform V2O5

  • V2O4 + 1/2O2 --> V2O5