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Detailed notes on The Periodic Table for Cambridge IGCSE Coordinated Science, covering key concepts, explanations, examples, and exam-focused revision points.
Transition elements are the d-block metals between Groups II and III. They have distinctive properties: variable oxidation states, coloured compounds, and catalytic behaviour. Cambridge tests these properties and how they differ from Group I metals.
Mapped to the Cambridge IGCSE 0654 syllabus (2025-2027).
Transition elements are hard, dense metals with high melting points, variable oxidation states, and coloured compounds — contrasting sharply with Group I alkali metals.
Transition elements occupy the d-block of the periodic table (periods 4-6, between Groups II and III). Common examples: Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn.
Comparison with Group I (alkali) metals:
| Property | Transition elements | Group I (alkali metals) |
|---|---|---|
| Density | High (Fe = 7.9 g/cm³) | Low (Na = 0.97 g/cm³) |
| Melting point | High (Fe = 1538°C) | Low (Na = 98°C) |
| Hardness | Hard | Soft (cut with knife) |
| Reactivity with water | Less reactive | React vigorously |
| Oxidation states | Variable | Fixed (+1) |
| Compound colour | Often coloured | Usually white/colourless |
| Catalytic activity | Good catalysts | Poor catalysts |
Variable oxidation states:
Catalytic uses:
Verbatim phrases and definitions Cambridge mark schemes credit.
Paper 4: 'State THREE ways in which transition metals differ from Group I metals' (3 marks — any three from: higher density, higher MP, harder, variable oxidation states, coloured compounds). 'State the catalyst used in the Haber process and the temperature' (2 marks — iron; ~450°C). MCQ tests colour of specific ions.
Sources: Cambridge IGCSE Coordinated Sciences 0654 syllabus 2025-2027 (C9); 0654 Examiner Reports 2022-2024. Last reviewed 2026-05-14.
Step-by-step solutions to past-paper-style questions on transition elements , written exactly the way a tutor would explain them at the board.
Question
State THREE properties of transition metals that differ from those of Group I (alkali) metals.
Step-by-step solution
Step 1
Higher melting points: transition metals have very high melting points (e.g. Fe: 1535 °C) compared with Group I metals (e.g. Na: 98 °C).
Step 2
Higher density: transition metals are much denser (e.g. Fe: 7.9 g/cm³) than Group I metals (e.g. Na: 0.97 g/cm³, which floats on water).
Step 3
Less reactive: transition metals do not react vigorously with air or water at room temperature, unlike Na or K.
Step 4
Form coloured compounds: e.g. Fe²⁺ compounds are green, Cu²⁺ compounds are blue; Group I compounds are typically colourless.
Step 5
Variable oxidation states: e.g. iron forms Fe²⁺ and Fe³⁺; Group I metals form only +1 ions.
Answer
Transition metals: higher m.p., higher density, less reactive, form coloured compounds, variable oxidation states — all in contrast to Group I metals.
Question
Explain what is meant by 'variable oxidation states' in transition metals and give an example.
Step-by-step solution
Step 1
Transition metals can form ions with different positive charges (oxidation states) in their compounds.
Step 2
This arises because d-orbitals in transition metals allow different numbers of electrons to be lost with similar energies.
Step 3
Example: iron can form iron(II) (Fe²⁺, green compounds, e.g. FeSO₄) and iron(III) (Fe³⁺, orange/brown compounds, e.g. Fe₂O₃).
Answer
Transition metals form ions with multiple oxidation states; e.g. iron forms Fe²⁺ (iron(II)) and Fe³⁺ (iron(III)) — different compounds with different properties.
Question
State the role of iron in the Haber process and explain why using a catalyst is important industrially.
Step-by-step solution
Step 1
Iron is used as a catalyst in the Haber process: N₂ + 3H₂ ⇌ 2NH₃.
Step 2
The iron catalyst lowers the activation energy of the reaction, increasing the rate without being consumed.
Step 3
Without the catalyst, the reaction at 450 °C would be too slow for economic production; the catalyst allows a useful rate of NH₃ production at the compromise temperature.
Step 4
The catalyst is not consumed, so it does not need to be replaced frequently, reducing costs.
Answer
Iron catalyst lowers activation energy → faster rate at 450 °C; not consumed → economically viable NH₃ production.
Definitions to memorise and the exact keywords mark schemes credit for transition elements answers — sharpened from recent examiner reports for the 2026 0654 sitting.
An element in the d-block of the periodic table (central section, Periods 4–6). Characteristics: high melting point, high density, forms coloured ions, variable oxidation states, catalytic activity.
The ability of a transition metal to form ions with different positive charges (e.g. Fe²⁺/Fe³⁺, Cu⁺/Cu²⁺, Mn²⁺/Mn⁴⁺/Mn⁷⁺).
Transition metal ions absorb specific visible wavelengths, giving their solutions and compounds characteristic colours: Fe²⁺ (green), Fe³⁺ (yellow-brown), Cu²⁺ (blue), Mn²⁺ (very pale pink).
A catalyst in a different phase from the reactants (e.g. solid iron catalyst for gaseous N₂/H₂ in the Haber process). Reactants adsorb onto the catalyst surface.
An ion in which a central metal atom or ion is surrounded by ligands (molecules or ions that donate electron pairs); responsible for the colour of many transition metal compounds.
The traps other students keep falling into on transition elements questions — taken from recent Cambridge IGCSE 0654 examiner reports and mark schemes — and how to avoid them.
Why it happens
Zinc is in the d-block but only forms Zn²⁺; it has no variable oxidation states and forms colourless compounds.
How to avoid it
Cambridge IGCSE lists zinc among transition elements; however, note that Zn only has +2 oxidation state and its compounds are usually colourless. Focus examples on Fe, Cu, Mn.
0654 Examiner Report 2022
Why it happens
Students associate the blue colour of copper sulfate with all transition metal compounds.
How to avoid it
Fe²⁺ = green; Fe³⁺ = orange/brown; Cu²⁺ = blue; Mn²⁺ = pale pink. Learn each ion's colour specifically.
Why it happens
Students confuse catalyst with reactant.
How to avoid it
Catalysts are not consumed; they lower the activation energy and are regenerated. Iron catalyst in Haber process lasts for years before needing replacement.
The things students keep getting wrong in this sub-topic, answered.