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Transition metals - PowerPoint

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									Transition metals
  Form coloured ions
  Form complexes
  Have variable oxidation states
  Show catalytic activity
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
Changing oxidation states


[Fe(H2O)6]2+     [Fe(H2O)6]3+
   GREEN         VERY PALE VIOLET
Changing oxidation states


 [Cr(H2O)6]3+       [Cr(H2O)6]2+

 RUBY                  BLUE
Changing ligands.
  Changing ligand can usually change
  co-ordination number and colour.

 [Cu(H2O)6]2+          [CuCl4]2-
     BLUE                GREEN
   OCTAHEDRAL         TETRAHEDRAL
Changing ligands


 [Co(H2O)6]2+       [CoCl4]2-

 PINK                 BLUE
 OCTAHEDRAL        TETRAHEDRAL
Ligand change but no
co-ordination change


 [Cr(H2O)6]3+   [Cr(NH3)6]3+
 RUBY              PURPLE
 OCTAHEDRAL        OCTAHEDRAL
Colour changes arising as a
result of all three changes



 [Mn(H2O)6]2+         [MnO4]-
 VERY PALE PINK      PURPLE
 OCTAHEDRAL        TETRAHEDRAL
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.
Example
CuSO4(s) + excess H2O            [Cu(H2O)6]2+
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.
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-
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 -
Multidentate
  Contain many donor atoms
  Example is
   bis[di(carboxymethyl)amino]ethane
   commonly known as EDTA.
  EDTA is able to bond to metal ions from
   six donor atoms.
EDTA
 The EDTA4- anion has the formula

 -OOCCH                  CH2COO     -
       2
            NCH2CH2N
 -OOCCH                  CH2COO     -
       2


 with six donor sites(4O and 2N)and forms
  a 1:1 complex with metal(II) ions
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)6]3+ 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.
Its time to wake up!!!!!
   Work out the oxidation state of the
   metal in each ion below.
 Vanadium
 VO4 3-, [VO(H2O)5]2+, [V(H2O)6]3+
 Chromium
 CrO42- , [Cr(H2O)6]3+
 Iron
 [Fe(H2O)6]3+
Catalysis
  Homogeneous
  Heterogeneous
  Haber process uses Iron
  Contact process uses vanadium(V)oxide
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.

								
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