Transition metals

1
Transition metals

• Form coloured ions
• Form complexes
• Have variable oxidation states
• Show catalytic activity

2
Colour of ions

• When a colour change occurs in the reaction of
  a transition metal ion, there is a change in at
  least one of the following-
• Oxidation state
• Co-ordination number
• Ligand

3
Changing oxidation states

• Fe(H2O)62 Fe(H2O)63
• GREEN VERY PALE VIOLET

4
Changing oxidation states

• Cr(H2O)63 Cr(H2O)62
• RUBY BLUE

5
Changing ligands.

• Changing ligand can usually change
  co-ordination number and colour.
• Cu(H2O)62 CuCl42-
  BLUE GREEN
• OCTAHEDRAL TETRAHEDRAL

6
Changing ligands

• Co(H2O)62
  CoCl42-
• PINK BLUE
• OCTAHEDRAL TETRAHEDRAL

7
Ligand change but no co-ordination change

• Cr(H2O)63 Cr(NH3)63
• RUBY PURPLE
• OCTAHEDRAL OCTAHEDRAL

8
Colour changes arising as a result of all three
changes

• Mn(H2O)62
  MnO4-
• VERY PALE PINK PURPLE
• OCTAHEDRAL TETRAHEDRAL

9
Complex formation

• Complex compounds contain a central atom
  surrounded by ions or molecules called ligands.
• Ligands donate an electron pair to a metal
  forming a co-ordinate bond.
• The number of ligands bonded to the metal ion is
  called the co-ordination number.
• The co-ordination number exceeds its oxidation
  state.

10
Example

• CuSO4(s) excess H2O Cu(H2O)62
• White Blue
• Co-ordination number of Cu 6
• Oxidation state of Cu 2
• Each water molecule is donating an electron pair
  (one of its lone pairs)
• The bonds within the complex, i.e. the
• Cu-O and the O-H are covalent.

11
Unidentate ligands

• Ligands which have only one atom which can
  donate a pair of electrons is said to be
  unidentate.
• They include the following-
• H2O, NH3, Cl-, OH - and CN-

12
Bidentate ligands

• Ligands which contain two donor atoms
• they bond to the metal ion through two atoms
• Bidentate ligands include-
• 1,2-diaminoethane NH2CH2CH2NH2
• Ethanedioate(oxalate) ion COO -
• COO -

13
Multidentate

• Contain many donor atoms
• Example is bisdi(carboxymethyl)aminoethane
  commonly known as EDTA.
• EDTA is able to bond to metal ions from six donor
  atoms.

14
EDTA

• The EDTA4- anion has the formula
• -OOCCH2 CH2COO -
• NCH2CH2N
• -OOCCH2 CH2COO -
• with six donor sites(4O and 2N)and forms a 11
  complex with metal(II) ions

15
Variable oxidation states

• Oxidation state is the formal number of positive
  charges which must be given to the metal to
  satisfy electroneutrality .
• E.g Co(NH3)63 NH3 no charge, overall charge
  3 so Co is in 3 oxidation state.
• When transition metal ions undergo oxidation -
  reduction reactions the metal changes its
  oxidation state.

16
Its time to wake up!!!!!

• Work out the oxidation state of the metal in
  each ion below.
• Vanadium
• VO4 3-, VO(H2O)52, V(H2O)63
• Chromium
• CrO42- , Cr(H2O)63
• Iron
• Fe(H2O)63

17
Answers

• Vanadium
• VO4 3-, VO(H2O)52, V(H2O)63
• (V) (IV) (III)
• Chromium
• CrO42- , Cr(H2O)63
• (VI) (III)
• Iron
• Fe(H2O)63 (III)

18
Catalysis

• Homogeneous
• Heterogeneous
• Haber process uses Iron
• Contact process uses vanadium(V)oxide

19
Contact process

• Sulphur dioxide oxidised to sulphur by vanadium
  (v) oxide
• SO2 V2O5 SO3
  V2O4
• The vanadium has been reduced to vanadium(IV). It
  is oxidised back to the starting vanadium (V)
  oxide by oxygen
• 2V2O4 O2 2V2O5
• the vanadium(v)oxide is unchanged at the end of
  the reaction.