Transition MetalsOxford AQA IGCSE Chemistry: Revision notes
Section 1
Where are the transition metals?
The transition metals are the large block of metallic elements found in the centre of the periodic table, between Group 2 and Group 3. Familiar examples include iron (Fe), copper (Cu), zinc (Zn), nickel (Ni) and titanium (Ti).
- They are all metals, so they conduct heat and electricity and can be shaped by bending or hammering.
- Their position (centre block) distinguishes them from the main-group metals such as Group 1 and Group 2.
Section 2
Why can transition metal ions have different charges?
Unlike Group 1 metals, which always form ions with a single fixed charge (+1), many transition metals can form ions with different charges depending on the compound.
- Iron can form Fe²⁺ (iron(II)) or Fe³⁺ (iron(III)) ions.
- Copper can form Cu⁺ (copper(I)) or Cu²⁺ (copper(II)) ions, though Cu²⁺ is the more common one you will meet.
- This variable charge is shown in a compound's name using Roman numerals, e.g. iron(II) chloride vs iron(III) chloride.
Do not assume all transition metal ions carry the same charge as Group 1 or Group 2 metals — always check which Roman numeral (if any) is given in the compound's name.
Section 3
Why do transition metal compounds have colour?
A key identifying feature of transition metals is that they form coloured compounds, unlike most Group 1 and Group 2 compounds, which are typically white or colourless in solution.
- Copper compounds are typically blue (e.g. copper(II) sulfate solution is blue).
- Iron(II) compounds are typically pale green.
- Iron(III) compounds are typically orange/brown.
This colour is a useful way to help identify which transition metal ion is present in an unknown compound.
Section 4
Why are transition metals useful as catalysts?
Transition metals and their compounds are widely used as catalysts — substances that speed up chemical reactions without being used up themselves.
- Iron is the catalyst used in the Haber process (making ammonia).
- Nickel is used to catalyse the hydrogenation of vegetable oils (making margarine).
- Vanadium(V) oxide is used as the catalyst in the Contact process (making sulfuric acid).
Their usefulness as catalysts, alongside their variable ion charges, is linked to their electronic structure.
Exam answers often ask you to name a specific transition metal catalyst used in an industrial process — link the metal to the process (iron/Haber, nickel/hydrogenation, vanadium(V) oxide/Contact process).
Must Know
- Transition metals sit in the centre of the periodic table, between Group 2 and Group 3.
- Many transition metals form ions with different (variable) charges, e.g. Fe²⁺ and Fe³⁺.
- Transition metal compounds are typically coloured (e.g. blue copper compounds, green iron(II), orange/brown iron(III)).
- Transition metals and their compounds are widely used as catalysts (e.g. iron in the Haber process).
- These three features (variable charge, colour, catalytic use) together distinguish transition metals from Group 1 and Group 2 metals.
That's the notes covered.
Carry on to the next subtopic.