1. TRANSITION METAL
COMPLEXES

2. THE AQUEOUS CHEMISTRY OF IONS - HYDROLYSIS
when salts dissolve in water the ions are stabilised
this is because water molecules are polar
hydrolysis can occur and the resulting solution can become acidic
the greater charge density of the cation...
the greater the polarising power and
the more acidic the solution

3. THE AQUEOUS CHEMISTRY OF IONS
Theory aqueous metal ions attract water molecules
many have six water molecules surrounding them
these are known as hexaaqua ions
they are octahedral in shape
water acts as a Lewis Base – a lone pair donor
water forms a co-ordinate bond to the metal ion
metal ions accept the lone pair - Lewis Acids

4. THE AQUEOUS CHEMISTRY OF IONS
Theory aqueous metal ions attract water molecules
many have six water molecules surrounding them
these are known as hexaaqua ions
they are octahedral in shape
water acts as a Lewis Base – a lone pair donor
water forms a co-ordinate bond to the metal ion
metal ions accept the lone pair - Lewis Acids
Acidity as charge density increases, the cation has a greater attraction for water
and it weakens the O-H bond, this makes the H more acidic (more d+)
it can then be removed by solvent water molecules to form H3O+(aq).

5. HYDROLYSIS - EQUATIONS
M2+ ions [M(H2O)6]2+(aq) H2O(l) [M(H2O)5(OH)]+(aq) H3O+(aq)
the resulting solution will now be acidic as there are more protons in the water
this reaction is known as hydrolysis - the water causes the substance to split up
Stronger bases (e.g. CO32- , NH3 and OH¯ ) can remove further protons...

6. HYDROLYSIS - EQUATIONS
M3+ ions [M(H2O)6]3+(aq) H2O(l) [M(H2O)5(OH)]2+(aq) H3O+(aq)
the resulting solution will also be acidic as there are more protons in the water
this SOLUTION IS MORE ACIDIC due to the greater charge density of 3+ ions
Stronger bases (e.g. CO32- , NH3 and OH¯ ) can remove further protons...

7. HYDROLYSIS OF HEXAAQUA IONS
Lewis bases can attack the co-ordinated water molecules. Theoretically, a proton can be removed from each water molecule turning the water from a neutral molecule to a negatively charged hydroxide ion. This affects the overall charge on the complex ion.
[M(H2O)6]2+(aq) [M(OH)(H2O)5]+(aq) [M(OH)2(H2O)4](s)
[M(OH)2(H2O)4](s) [M(OH)3(H2O)3]¯(aq) [M(OH)4(H2O)2]2-(aq)
[M(OH)4(H2O)2]2-(aq) [M(OH)5(H2O)]3-(aq) [M(OH)6]4-(aq)
In some cases, if the base is strong, further protons are removed and the precipitate dissolves as soluble anionic complexes such as [M(OH)6]3- are formed.
Very weak bases H2O remove few protons
Weak bases NH3, CO32- remove protons until precipitation
Strong bases OH¯ can remove all the protons
OH¯ H+
OH¯ H+
Precipitated
OH¯ H+
OH¯ H+
OH¯ H+
OH¯ H+

8. HYDROLYSIS OF HEXAAQUA IONS
AMPHOTERIC CHARACTER
Metal ions of 3+ charge have a high charge density and their hydroxides can dissolve in both acid and alkali. Aluminium hydroxides show this property.
[M(H2O)6]3+(aq) [M(OH)3(H2O)3](s) [M(OH)6]3-(aq) H+
OH¯
Soluble
Insoluble
Soluble

9. REACTION TYPES • shape • stability to oxidation or reduction
One typical property of transition elements is their ability to form complex ions.
Complex ions consist of a central metal ion surrounded by co-ordinated ions or molecules known as ligands. This can lead to changes in ...
• colour • co-ordination number
• shape • stability to oxidation or reduction
Reaction
types
ACID-BASE
LIGAND SUBSTITUTION
PRECIPITATION
A-B LS
Ppt

10. REACTIONS OF COPPER(II)
Aqueous solutions of copper(II) contain the blue, octahedral hexaaquacopper(II) ion
Most substitution reactions are similar to cobalt(II).
OH¯ [Cu(H2O)6]2+(aq) OH¯(aq) ——> [Cu(OH)2(H2O)4](s) H2O(l)
blue, octahedral pale blue ppt.
insoluble in XS NaOH
NH3 [Cu(H2O)6]2+(aq) NH3(aq) ——> [Cu(OH)2(H2O)4](s) NH4+(aq)
blue ppt. soluble in excess NH3
then [Cu(OH)2(H2O)4](s) + 4NH3(aq) ——> [Cu(NH3)4(H2O)2]2+(aq) + 2H2O(l) + 2OH¯(aq) royal blue NOTE THE FORMULA
CO32- [Cu(H2O)6]2+(aq) CO32-(aq) ——> CuCO3(s) H2O(l)
blue ppt.
A-B
A-B LS
Ppt

11. REACTIONS OF COPPER(II)
Cl¯ [Cu(H2O)6]2+(aq) + 4Cl¯(aq) ——> [CuCl4]2-(aq) H2O(l) yellow, tetrahedral
• Cl¯ ligands are larger than H2O and are charged
• the complex is more stable if the shape changes to tetrahedral
• adding excess water reverses the reaction LS

12. REACTIONS OF IRON(II)
When iron reacts with acids it gives rise to iron(II) (ferrous) salts.
Aqueous solutions of such salts contain the pale green, octahedral hexaaquairon(II) ion
OH¯ [Fe(H2O)6]2+(aq) OH¯(aq) ——> [Fe(OH)2(H2O)4](s) H2O(l)
pale green dirty green ppt.
it only re-dissolves in very conc. OH¯ but...
it slowly turns a rusty brown colour due to oxidation by air to iron(III)
increasing the pH renders iron(II) unstable.
Fe(OH)2(s) + OH¯(aq) ——> Fe(OH)3(s) e¯
dirty green rusty brown
NH3 Iron(II) hydroxide precipitated, insoluble in excess ammonia
CO32- Off-white coloured iron(II) carbonate, FeCO3, precipitated
A-B OX
A-B
Ppt

13. REACTIONS OF IRON(III)
Aqueous solutions contain the yellow-green, octahedral hexaaquairon(III) ion
OH¯ [Fe(H2O)6]3+(aq) OH¯(aq) ——> [Fe(OH)3(H2O)3](s) H2O(l)
yellow rusty-brown ppt. insoluble in XS
CO32- 2[Fe(H2O)6]3+(aq) + 3CO32-(aq) ——> 2[Fe(OH)3(H2O)3](s) H2O(l) + 3CO2(g) rusty-brown ppt.
The carbonate is not precipitated but the hydroxide is; the high
charge density of M3+ makes the solution too acidic to form a carbonate
CARBON DIOXIDE EVOLVED.
NH3 [Fe(H2O)6]3+(aq) NH3(aq) ——> [Fe(OH)3(H2O)3](s) NH4+(aq)
rusty-brown ppt. insoluble in XS
SCN¯ [Fe(H2O)6]3+(aq) SCN¯(aq) ——> [Fe(SCN)(H2O)5]2+(aq) + H2O(l)
blood-red colour
Very sensitive; BLOOD RED COLOUR confirms Fe(III). No reaction with Fe(II)
A-B
A-B
A-B LS

14. REACTIONS OF SILVER(I)
• aqueous solutions contains the colourless, linear, diammine silver(I) ion
• formed when silver halides dissolve in ammonia
eg AgCl(s) NH3(aq) ——> [Ag(NH3)2]+(aq) Cl¯(aq)
[Ag(NH3)2] Used in Tollen’s reagent (SILVER MIRROR TEST)
Tollen’s reagent is used to differentiate between aldehydes and ketones.
Aldehydes produce a silver mirror on the inside of the test tube
Formed when silver halides dissolve in ammonia - TEST FOR HALIDES

15. REACTIONS OF ALUMINIUM
• aluminium is not a transition metal as it doesn’t make use of d orbitals
• BUT, due to a high charge density, aluminium ions behave as typical M3+ ions
• aqueous solutions contain the colourless, octahedral hexaaquaaluminium(III) ion
OH¯ [Al(H2O)6]3+(aq) OH¯(aq) ——> [Al(OH)3(H2O3](s) H2O(l)
colourless, octahedral white ppt. soluble in XS NaOH
As with all hydroxides the precipitate reacts with acid
[Al(OH)3(H2O)3](s) H+ (aq) ——> [Al(H2O)6]3+(aq)
being a 3+ hydroxide it is AMPHOTERIC and dissolves in excess alkali
[Al(OH)3(H2O)3](s) OH¯(aq) ——> [Al(OH)6]3-(aq) H2O(l)
colourless, octahedral
CO [Al(H2O)6]3+(aq) CO32-(aq) ——> 2[Al(OH)3(H2O)3](s) H2O(l) + 3CO2(g)
As with 3+ ions, the carbonate is not precipitated but the hydroxide is.
NH3 [Al(H2O)6]3+(aq) NH3(aq) ——> [Al(OH)3(H2O)3](s) + 3NH4+(aq) white ppt. insoluble in XS NH3
A-B
A-B
A-B
A-B
A-B