Transition metals have characteristic properties that distinguish them from other metals, such as those in Group 1. Explain why transition metals are able to form ions with different oxidation states, and describe how this property makes them useful as catalysts.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Manganese is a transition metal used in the manufacture of steel and in certain industrial chemical processes. It can form ions including Mn²⁺, Mn³⁺, and Mn⁴⁺.
Model answer (5 marks)
Transition metals have incompletely filled d sub‑levels, so d electrons can be lost or gained.
The d orbitals are close in energy, allowing different numbers of electrons to be removed or added.
Thus transition metal ions can change oxidation state during a reaction, e.g. Mn²⁺ ↔ Mn³⁺.
As a catalyst the metal ion accepts electrons from (or donates to) reactants, providing an alternative reaction pathway.
The metal ion is regenerated at the end of the reaction, returning to its original oxidation state and not being consumed.
The d orbitals are close in energy, allowing different numbers of electrons to be removed or added.
Thus transition metal ions can change oxidation state during a reaction, e.g. Mn²⁺ ↔ Mn³⁺.
As a catalyst the metal ion accepts electrons from (or donates to) reactants, providing an alternative reaction pathway.
The metal ion is regenerated at the end of the reaction, returning to its original oxidation state and not being consumed.
Examiner tips
- Use the phrase ‘incompletely filled d sub‑levels’ and ‘close in energy’ to hit the first two marks.
- Show the change of oxidation state with an example such as Mn²⁺ ↔ Mn³⁺ to secure the third mark.
- Explain the electron transfer step and the alternative pathway for the fourth mark.
- Mention regeneration of the metal ion for the final mark.
Mark scheme (5 marks)
- Transition metals have incompletely filled d sub-levels (d orbitals) / d electrons can be lost or gained
- The energy levels of the d orbitals are close together / similar in energy, so different numbers of electrons can be removed
- This means transition metal ions can change oxidation state during a reaction / switch between different ions (e.g. Mn²⁺ and Mn³⁺)
- As a catalyst, the transition metal ion accepts electrons from (or donates electrons to) reactants / provides an alternative reaction pathway
- The transition metal ion is regenerated at the end of the reaction / returns to its original oxidation state, so it is not used up
Key terms in this question
transition metal · oxidation state · catalyst
Related
- All Edexcel A-Level Chemistry (9CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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