CIE iGCSE Co-ordinated Sciences-C8.4 Transition elements- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-C8.4 Transition elements – Study Notes
CIE iGCSE Co-ordinated Sciences-C8.4 Transition elements – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Transition Elements
Transition elements are metals found in the central d-block of the Periodic Table, between Groups 3 and 12. They are characterised by having partially filled d-orbitals, which give rise to their distinctive chemical and physical properties.
Key Physical Properties:
- High densities: Transition metals are generally very dense due to their closely packed metallic crystal structures and relatively high atomic masses. For example, iron has a density of 7.87 g/cm³, and platinum is 21.45 g/cm³.
- High melting and boiling points: Strong metallic bonding involving delocalised d-electrons leads to high melting and boiling points. The presence of partially filled d-orbitals contributes to stronger bonding. Mercury is an exception, with a low melting point (-39 °C) due to weak interatomic forces in its liquid state.
Chemical Properties:
- Formation of coloured compounds: The partially filled d-orbitals allow d–d electron transitions when light is absorbed. Different wavelengths of visible light are absorbed, producing coloured compounds. For example, copper(II) sulfate is blue, and chromium(III) chloride is green.
- Variable oxidation states: Many transition elements can exhibit more than one oxidation state in their compounds. For instance, iron can form Fe²⁺ and Fe³⁺ ions, while manganese can form Mn²⁺, Mn³⁺, Mn⁴⁺, Mn⁶⁺, and Mn⁷⁺. This is due to the involvement of d-electrons in bonding.
- Catalytic activity: Transition metals and their compounds frequently act as catalysts. This is due to their ability to lend and accept electrons via multiple oxidation states and to provide a surface for reactions (heterogeneous catalysis). For example,
- Iron is used as a catalyst in the Haber process for ammonia production.
- Vanadium(V) oxide (V₂O₅) is used as a catalyst in the contact process for sulfuric acid production.
- Formation of complex ions: Transition metals readily form complex ions with ligands due to the availability of empty d-orbitals, further contributing to coloured solutions and catalytic properties.
Example
Explain why copper(II) sulfate solution is blue.
▶️Answer/Explanation
Copper(II) ions have partially filled d-orbitals. Light absorption excites electrons between these d-orbitals (d–d transitions), absorbing certain wavelengths. The transmitted or reflected light appears blue, giving copper(II) sulfate its characteristic colour.
Example
Describe why iron is used as a catalyst in the Haber process.
▶️Answer/Explanation
Iron acts as a heterogeneous catalyst by providing a surface where nitrogen and hydrogen gases can adsorb. Its partially filled d-orbitals enable temporary bonding and electron transfer, weakening the strong N≡N triple bond. This accelerates the formation of ammonia without the iron being consumed in the reaction.
Example
Explain the trend in densities and melting points among transition metals.
▶️Answer/Explanation
Transition metals have strong metallic bonding due to delocalised d-electrons, which also allows tight atomic packing. This results in high densities and high melting/boiling points. Slight variations occur depending on the number of unpaired d-electrons and atomic radius, but in general, transition metals are denser and melt at higher temperatures than s-block metals.