Chemistry Form 4: Chapter 4 - Special Characteristics of Transition Elements

 

1.  Transition elements can form coloured compounds

2.  Transition elements have varying oxidation number

• Iron has two common oxidation states (+2 and +3) in, for example, Fe²⁺ and Fe³⁺. It also has a less common +6 oxidation state in the ferrate(VI) ion, FeO₄^2-.
• Manganese has a very wide range of oxidation states in its compounds. For example:

+2	in Mn2+
+3	in Mn2O3
+4	in MnO2
+6	in MnO42-
+7	in MnO4-

3.  Transition elements can form complex ions

• A complex ion has a metal ion at its centre with a number of other molecules or ions surrounding it. 
• Some examples of complex ions formed by transition metals
  

  
  

  [Fe(H₂O)₆]²⁺,   [Co(NH₃)₆]²⁺,   [Cr(OH)₆]^3- ,  [CuCl₄]^2-

4.  Transition elements can act as catalysts

• Iron in the Haber Process
  The Haber Process combines hydrogen and nitrogen to make ammonia using an iron catalyst.
                           

• Vanadium(V) oxide in the Contact Process
  At the heart of the Contact Process is a reaction which converts sulphur dioxide into sulphur trioxide. Sulphur dioxide gas is passed together with air (as a source of oxygen) over a solid vanadium(V) oxide catalyst.
  
                

• Nickel in the hydrogenation of C=C bonds
  This reaction is at the heart of the manufacture of margarine from vegetable oils.
  However, the simplest example is the reaction between ethene and hydrogen in the presence of a nickel catalyst.