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This lesson covers the transition metals as required by the Edexcel GCSE Chemistry specification (1CH0), Topic 6: Groups in the Periodic Table. You need to know the typical properties of transition metals, understand how they differ from Group 1 metals, and recall examples of their coloured compounds, variable oxidation states and catalytic activity.
The transition metals are found in the central block of the periodic table, between Group 2 and Group 3. This block includes well-known metals such as iron, copper, nickel, zinc, chromium, manganese, cobalt and platinum.
Strictly, zinc is sometimes excluded from the transition metals by a precise chemical definition, but at GCSE level it is typically included when discussing the properties of this block of elements.
The transition metals form a large block spanning periods 4 to 7 horizontally. The most commonly studied examples at GCSE are from Period 4:
| Element | Symbol | Atomic Number | Common Ion(s) |
|---|---|---|---|
| Titanium | Ti | 22 | Ti⁴⁺ |
| Chromium | Cr | 24 | Cr³⁺, Cr⁶⁺ |
| Manganese | Mn | 25 | Mn²⁺, Mn⁴⁺, Mn⁷⁺ |
| Iron | Fe | 26 | Fe²⁺, Fe³⁺ |
| Cobalt | Co | 27 | Co²⁺, Co³⁺ |
| Nickel | Ni | 28 | Ni²⁺ |
| Copper | Cu | 29 | Cu⁺, Cu²⁺ |
| Zinc | Zn | 30 | Zn²⁺ |
Exam Tip: You do not need to memorise the electron configurations of transition metals for GCSE, but you must know their key properties and be able to give examples.
Transition metals share a set of characteristic properties that distinguish them from the alkali metals of Group 1.
Transition metals have high melting points — much higher than Group 1 metals. This is because they have strong metallic bonds due to their small atomic radii and the large number of delocalised electrons.
| Metal | Melting Point (°C) |
|---|---|
| Iron | 1 538 |
| Copper | 1 085 |
| Nickel | 1 455 |
| Chromium | 1 907 |
| Sodium (Group 1) | 98 |
| Potassium (Group 1) | 63 |
Transition metals are dense. Their atoms are relatively small and tightly packed, with heavy nuclei.
| Metal | Density (g/cm³) |
|---|---|
| Iron | 7.87 |
| Copper | 8.96 |
| Gold | 19.32 |
| Sodium (Group 1) | 0.97 |
Transition metals are hard, strong and tough. They are much harder than the alkali metals, which are soft enough to cut with a knife. This makes transition metals useful as structural materials (e.g. iron in construction, titanium in aircraft).
Like all metals, transition metals are good conductors of heat and electricity. Copper is an excellent electrical conductor, which is why it is used in wiring and electrical circuits.
One of the most distinctive properties of transition metals is that they form coloured compounds and ions in solution.
| Compound | Formula | Colour |
|---|---|---|
| Copper(II) sulfate | CuSO₄ | Blue |
| Copper(II) hydroxide | Cu(OH)₂ | Blue (precipitate) |
| Iron(II) sulfate | FeSO₄ | Pale green |
| Iron(II) hydroxide | Fe(OH)₂ | Green (precipitate) |
| Iron(III) chloride | FeCl₃ | Yellow/brown |
| Iron(III) hydroxide | Fe(OH)₃ | Brown (precipitate) |
| Potassium dichromate | K₂Cr₂O₇ | Orange |
| Potassium manganate(VII) | KMnO₄ | Purple |
| Nickel(II) sulfate | NiSO₄ | Green |
| Cobalt(II) chloride | CoCl₂ | Blue (anhydrous) / Pink (hydrated) |
By contrast, compounds of Group 1 metals are typically white when solid and colourless when dissolved in water. For example, sodium chloride (NaCl) is white and dissolves to give a colourless solution.
Exam Tip: Being able to identify transition metal compounds by their colour is useful for practical exam questions. The most commonly tested are: copper(II) compounds are blue, iron(II) compounds are green, and iron(III) compounds are brown/yellow.
Transition metals can form ions with different charges (variable oxidation states). This is unlike Group 1 metals, which always form 1+ ions.
The most important examples at GCSE are:
| Metal | Possible Ions | Examples of Compounds |
|---|---|---|
| Iron | Fe²⁺ (iron(II)) and Fe³⁺ (iron(III)) | FeSO₄ (green) and Fe₂O₃ (red-brown) |
| Copper | Cu⁺ (copper(I)) and Cu²⁺ (copper(II)) | Cu₂O (red) and CuSO₄ (blue) |
| Manganese | Mn²⁺, Mn⁴⁺, Mn⁷⁺ | MnO₂ (black), KMnO₄ (purple) |
| Chromium | Cr³⁺, Cr⁶⁺ | Cr₂O₃ (green), K₂Cr₂O₇ (orange) |
The Roman numeral in the name tells you the charge on the metal ion:
Exam Tip: When naming compounds containing transition metals, include the Roman numeral if the metal can form more than one type of ion. For example, "iron oxide" is ambiguous — always write "iron(II) oxide" (FeO) or "iron(III) oxide" (Fe₂O₃).
Many transition metals and their compounds are used as catalysts — substances that speed up chemical reactions without being used up.
| Catalyst | Reaction It Catalyses |
|---|---|
| Iron (Fe) | The Haber process: N₂ + 3H₂ ⇌ 2NH₃ (making ammonia) |
| Manganese dioxide (MnO₂) | Decomposition of hydrogen peroxide: 2H₂O₂ → 2H₂O + O₂ |
| Vanadium pentoxide (V₂O₅) | The Contact process: 2SO₂ + O₂ → 2SO₃ (making sulfuric acid) |
| Nickel (Ni) | Hydrogenation of vegetable oils (making margarine) |
| Platinum (Pt) | Catalytic converters in car exhausts |
Catalysts are important in industrial chemistry because they:
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