Transition Metals
Summary: Transition metals are hard, dense, high-melting, form coloured compounds, have variable oxidation states, and act as catalysts. Examples: Fe, Cu, Mn, Cr, Ni, Co, Ti. Tags: igcse chemistry periodic-table Created: 2026-07-14 Last Updated: 2026-07-16
Position in the Periodic Table
Transition metals are found in the central block of the Periodic Table, between Group 2 and Group 3 (Group 13). This region is called the d-block. They are all metals.
Common transition metals for IGCSE: Iron (Fe), Copper (Cu), Zinc (Zn), Manganese (Mn), Chromium (Cr), Nickel (Ni), Cobalt (Co), Titanium (Ti).
Zinc is technically a transition metal by position but does not show all typical transition metal properties (e.g., its compounds are white, not coloured, because it has a full d-subshell — Zn2+ = 3d10). IGCSE treats it as part of the transition metals for position.
Comparison: Transition Metals vs Group 1 Metals
Transition metals differ dramatically from Group 1 (alkali) metals.
| Property | Group 1 Metals (e.g., Na, K) | Transition Metals (e.g., Fe, Cu) |
|---|---|---|
| Melting point | Low (Na: 98 °C, K: 63 °C) | Much higher (Fe: 1538 °C, Cu: 1085 °C) |
| Boiling point | Low (Na: 883 °C) | Much higher (Fe: 2862 °C) |
| Density | Low (Na: 0.97 g/cm³ — floats on water) | Much higher (Fe: 7.87 g/cm³, Cu: 8.96 g/cm³) |
| Hardness | Soft (can be cut with a knife) | Hard (Fe and Cu are much harder) |
| Strength | Weak | Strong — used for construction, bridges, etc. |
| Reactivity | Very reactive — react vigorously with water | Much less reactive — most do not react with cold water |
| Reaction with water | All react (Na vigorously, K violently) | Do not react with cold water (some, like Fe, react slowly with steam) |
| Reaction with acids | React explosively | React slowly (if at all — Cu does not react with dilute HCl or H2SO4) |
| Colour of compounds | White / colourless | Coloured — e.g., blue (Cu2+), green (Fe2+), brown (Fe3+), purple (MnO4-) |
| Oxidation states | Only one: +1 | Variable — e.g., Fe can be +2 or +3; Cu can be +1 or +2; Mn has many (+2, +4, +6, +7) |
| Catalytic activity | Generally not catalysts | Many are good catalysts (Fe, Ni, V2O5, MnO2, Pt) |
| Formation of complex ions | Rare | Common — e.g., [Cu(NH3)4]2+ deep blue, [CuCl4]2- yellow-green |
| Malleability / ductility | Malleable and ductile | Malleable and ductile (like all metals) |
| Conductivity (heat/electricity) | Good conductors | Good conductors (Cu is one of the best electrical conductors) |
Coloured Compounds
The colour of transition metal compounds is one of their most distinctive features. Transition metal ions have partially filled d-orbitals. When visible light strikes the compound, electrons in the d-orbitals absorb certain wavelengths and are promoted to higher energy levels. The light that is not absorbed is transmitted/reflected and is the colour observed.
Key colours to know for IGCSE:
| Ion / Compound | Formula | Colour |
|---|---|---|
| Copper(II) ions | Cu2+ (aq) | Blue |
| Copper(II) sulfate crystals | CuSO4·5H2O | Blue (hydrated); white when anhydrous (CuSO4) |
| Copper(II) oxide | CuO | Black solid |
| Copper(II) carbonate | CuCO3 | Green solid |
| Iron(II) ions | Fe2+ (aq) | Pale green |
| Iron(III) ions | Fe3+ (aq) | Orange / yellow-brown (rust-coloured) |
| Iron(II) hydroxide | Fe(OH)2 | Green precipitate |
| Iron(III) hydroxide | Fe(OH)3 | Red-brown / orange-brown precipitate (rust) |
| Manganate(VII) ions | MnO4- (aq) | Purple (potassium manganate(VII) = KMnO4, an oxidising agent) |
| Chromate(VI) ions | CrO4 2- (aq) | Yellow |
| Dichromate(VI) ions | Cr2O7 2- (aq) | Orange |
| Cobalt(II) ions | Co2+ (aq) | Pink |
| Nickel(II) ions | Ni2+ (aq) | Green |
Variable Oxidation States
Transition metals can form ions with different charges (oxidation states). This is because the energy difference between their outer s-electrons and d-electrons is small, allowing different numbers of electrons to be lost.
| Element | Common Oxidation States | Examples |
|---|---|---|
| Iron (Fe) | +2 and +3 | Fe2+ (iron(II)) — pale green; Fe3+ (iron(III)) — orange/brown |
| Copper (Cu) | +1 and +2 | Cu+ (copper(I)); Cu2+ (copper(II)) — blue |
| Manganese (Mn) | +2, +4, +6, +7 | MnO4- (manganate(VII)) — purple; MnO2 (manganese(IV) oxide) — brown/black |
| Chromium (Cr) | +3, +6 | Cr3+ — green; CrO4 2- (chromate(VI)) — yellow; Cr2O7 2- (dichromate(VI)) — orange |
Naming: Roman numerals in brackets indicate the oxidation state. For example, iron(III) chloride = FeCl3 (Fe is +3); iron(II) chloride = FeCl2 (Fe is +2).
This contrasts with Group 1 metals, which only ever form +1 ions (e.g., Na is always Na+ in compounds).
Catalytic Activity
Many transition metals and their compounds are excellent catalysts — they speed up chemical reactions without being used up.
| Catalyst | Process Catalysed | Equation / Reaction |
|---|---|---|
| Iron (Fe) | Haber process (manufacture of ammonia) | N2(g) + 3H2(g) ⇌ 2NH3(g) |
| Nickel (Ni) | Hydrogenation of alkenes (manufacture of margarine from vegetable oils) | C2H4 + H2 → C2H6 (alkene + H2 → alkane) |
| Vanadium(V) oxide (V2O5) | Contact process (manufacture of sulfuric acid) | 2SO2(g) + O2(g) ⇌ 2SO3(g) |
| Manganese(IV) oxide (MnO2) | Decomposition of hydrogen peroxide | 2H2O2(aq) → 2H2O(l) + O2(g) |
| Platinum (Pt) / Palladium (Pd) / Rhodium (Rh) | Catalytic converters in car exhausts | 2CO + 2NO → 2CO2 + N2; 2CO + O2 → 2CO2 |
| Copper (Cu) | Manufacture of methanol from synthesis gas | CO + 2H2 → CH3OH |
How heterogeneous catalysts work (IGCSE level):
- Reactant molecules are adsorbed onto the surface of the solid catalyst.
- Bonds in the reactant molecules are weakened.
- Reaction occurs on the catalyst surface.
- Product molecules desorb (leave) the catalyst surface.
- The catalyst remains unchanged and can be reused.
Key Transition Metals in Detail
Iron (Fe)
Iron is the most used metal in the world. It is extracted from iron ore (mainly haematite, Fe2O3) in a blast furnace.
Extraction (blast furnace):
- Raw materials: iron ore (Fe2O3), coke (carbon), limestone (CaCO3)
- Coke burns to produce CO2 and then CO: C + O2 → CO2; CO2 + C → 2CO
- CO reduces the iron oxide: Fe2O3 + 3CO → 2Fe + 3CO2
- Limestone removes impurities (slag formation): CaCO3 → CaO + CO2; CaO + SiO2 → CaSiO3 (slag)
Properties of iron:
- Magnetic (can be magnetised)
- Relatively soft in pure form
- Rusts in the presence of water and oxygen: 4Fe + 3O2 + 2xH2O → 2Fe2O3·xH2O (hydrated iron(III) oxide)
Alloys of iron:
- Steel: iron + carbon (typically 0.2-2% carbon) — much stronger and harder than pure iron
- Stainless steel: iron + chromium + nickel — resistant to rusting/corrosion
- Mild steel: ~0.2% carbon — used for car bodies, girders
- High-carbon steel: ~0.6-1% carbon — harder, used for cutting tools
Copper (Cu)
Copper is an excellent conductor of electricity and heat.
Properties:
- Red-brown / pinkish metal
- Very good electrical conductor (second only to silver among pure metals at room temperature) — widely used for electrical wiring
- Good thermal conductor — used in cooking utensils, heat exchangers
- Malleable and ductile — can be drawn into thin wires
- Does not react with water or dilute hydrochloric acid or dilute sulfuric acid (it is below hydrogen in the reactivity series)
Uses:
- Electrical wiring (excellent conductor)
- Plumbing / water pipes (does not corrode easily; malleable)
- Cooking pots and pans (good heat conductor)
- Roofing and statues (weathers to form a green patina — copper carbonate)
Alloys of copper:
- Brass: copper + zinc — harder than pure copper; used for musical instruments, door handles, ornaments
- Bronze: copper + tin — harder and more corrosion-resistant; used for statues, ship propellers, coins
Zinc (Zn)
Zinc is used mainly for protecting iron and steel from rusting.
Key use — Galvanising:
- Galvanising is coating iron or steel with a layer of zinc.
- Zinc provides sacrificial protection: zinc is more reactive than iron, so zinc corrodes preferentially (is “sacrificed”), leaving the iron protected. Even if the zinc layer is scratched, the exposed iron is still protected because zinc will still corrode first.
- This is different from a barrier method (like painting), which only works as long as the coating is intact.
Zinc is also used in:
- Brass (alloy with copper)
- Batteries (zinc-carbon and zinc-air batteries)
- Die-casting (e.g., toy cars, door handles)
Zinc extraction:
- Zinc is extracted from zinc blende (ZnS). It is roasted in air to form ZnO, then reduced with carbon: 2ZnS + 3O2 → 2ZnO + 2SO2; ZnO + C → Zn + CO.
Chromium (Cr)
- Used in stainless steel (with Fe and Ni) — provides resistance to corrosion
- Chromium plating provides a shiny, corrosion-resistant decorative coating (e.g., on car bumpers, bathroom fittings)
- Chromium compounds have distinctive colours: chromate(VI) (CrO4 2-) = yellow; dichromate(VI) (Cr2O7 2-) = orange
Titanium (Ti)
- Very strong but lightweight metal
- Resistant to corrosion (used in aircraft, jet engines, hip replacements, and dental implants)
- Titanium(IV) oxide (TiO2) is a brilliant white pigment used in paints, sunscreen, and food colouring
Summary Comparison Table
| Property | Potassium (K, Group 1) | Iron (Fe, Transition) | Copper (Cu, Transition) |
|---|---|---|---|
| Melting point (°C) | 63 | 1538 | 1085 |
| Density (g/cm³) | 0.86 | 7.87 | 8.96 |
| Reaction with cold water | Violent reaction, ignites | No reaction | No reaction |
| Reaction with dilute HCl | Explosive | Slow reaction → FeCl2 + H2 | No reaction |
| Colour of compounds | White/colourless | Coloured (Fe2+ green, Fe3+ orange/brown) | Coloured (Cu2+ blue) |
| Oxidation states | +1 only | +2, +3 | +1, +2 |
| Catalytic use | None | Haber process (ammonia) | Methanol production |
| Alloys | Not commonly alloyed | Steel, stainless steel | Brass, bronze |
Key Points
- Transition metals are between Group 2 and Group 3 in the Periodic Table
- Compared with Group 1: transition metals have higher mp/bp, higher density, are harder/stronger, are less reactive, form coloured compounds, have variable oxidation states, and are good catalysts
- Colours: Cu2+ = blue, Fe2+ = pale green, Fe3+ = orange/brown, MnO4- = purple, CrO4 2- = yellow, Cr2O7 2- = orange
- Catalysts: Fe (Haber process), Ni (hydrogenation), V2O5 (Contact process), MnO2 (H2O2 decomposition), Pt/Pd/Rh (catalytic converters)
- Iron: extracted in blast furnace; Fe2O3 + 3CO → 2Fe + 3CO2; alloys: steel, stainless steel
- Copper: excellent conductor; alloys: brass (+Zn), bronze (+Sn)
- Zinc: galvanising (sacrificial protection); alloy: brass (+Cu)
- Transition metals form ions with different charges — named using Roman numerals
Key Concepts from Past Papers
- Transition metals form coloured compounds and act as catalysts
- Iron extracted in blast furnace using coke, limestone, and haematite
Keywords from Past Papers
copper, iron, reactive, oxide, high, oxygen, carbon, zinc, chlorine, bromine, magnesium, metal, aluminium, reverse, argument
Related Notes
Sources
- OpenStax Chemistry 2e — [Chapter 19: Transition Metals and Coordination Chemistry], Rice University (free, CC BY 4.0)
- BBC Bitesize GCSE Chemistry — [Transition Metals], BBC (free educational resource)
- Cambridge IGCSE Chemistry 0620 — Syllabus Section 9: The Periodic Table (Transition Metals), Cambridge Assessment International Education
- CK-12 Chemistry for High School — [Chapter 4: Transition Metals], CK-12 Foundation (free, CC BY-NC 3.0)
Past Paper Sources
- 0620/31 May/June 2015: Q11(c)(ii) (0m), Q33(a)(i) (0m), Q33(a)(ii) (0m) (+2 more)
- 0620/32 Feb/March 2015: Q44(b)(iv) (2m), Q55(a)(i) (2m), Q55(a)(iii) (2m) (+9 more)
- 0620/32 Feb/March 2017: Q11(a)(iii) (1m), Q11(a)(v) (1m), Q22(e)(i) (1m) (+1 more)
- 0620/32 Feb/March 2018: Q22(a)(iii) (1m), Q55(a)(iii) (1m), Q55(b)(i) (1m) (+3 more)
- 0620/32 Feb/March 2019: Q33(c)(iii) (4m), Q66(a)(i) (1m), Q66(b)(i) (1m) (+1 more)
- 0620/32 Feb/March 2020: Q22(b)(i) (1m), Q22(d)(i) (1m), Q66(a)(iv) (0m) (+1 more)
- 0620/32 Feb/March 2021: Q55(f)(i) (1m), Q77(e)(iii) (1m), Q66(c)(ii) (0m)
- 0620/32 Feb/March 2022: Q33(b)(ii) (1m), Q88(d)(iii) (1m)
- 0620/32 Feb/March 2023: Q77(a)(ii) (4m)
- 0620/32 May/June 2018: Q88(e)(iii) (0m)
- 0620/32 May/June 2020: Q11(a)(iv) (1m), Q88(e)(ii) (0m)
- 0620/33 May/June 2016: Q33(b)(ii) (1m), Q44(c)(i) (1m), Q77(d)(i) (1m) (+1 more)
Common Misconceptions
| Misconception | Reality |
|---|---|
| ”Transition metals are all in Group 3” | They are in the central block between Group 2 and Group 3 — not a single group. |
| ”Zinc is not a transition metal” | Zinc is in the d-block and is positioned among the transition metals. However, it does not form coloured compounds or have variable oxidation states (only Zn2+) because it has a full d-subshell. IGCSE treats it as a transition metal by position. |
| ”All metals react with acids” | Copper does not react with dilute hydrochloric acid or dilute sulfuric acid — it is below hydrogen in the reactivity series. |
| ”Galvanising is the same as painting — just a barrier” | Galvanising provides sacrificial protection as well as a barrier. Zinc corrodes in preference to iron because it is more reactive. |
| ”Iron is extracted by electrolysis” | Iron is extracted by reduction with carbon/carbon monoxide in a blast furnace. Electrolysis is too expensive for iron. Aluminium, by contrast, must be extracted by electrolysis. |