Monday, May 2, 2011

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, FeO42-.
  • Manganese has a very wide range of oxidation states in its compounds. For example:
+2in Mn2+
+3in Mn2O3
+4in MnO2
+6in MnO42-
+7in 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.


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