Transition metals (HT)
The transition metals occupy the central block of the periodic table — Sc to Zn in period 4, and similar rows in periods 5 and 6. Common examples at GCSE: iron (Fe), copper (Cu), nickel (Ni), zinc (Zn), titanium (Ti) and chromium (Cr).
Their behaviour is very different from Group 1 metals (alkali metals), and this comparison is a frequent HT exam question.
Typical properties of transition metals
- High melting and boiling points (Fe melts at 1538 °C, Cu at 1085 °C; vs Na at 98 °C).
- High density (Cu density 8.9 g/cm³ vs Li density 0.5 g/cm³).
- Hard and strong (used as structural metals; alloys e.g. steel from Fe).
- Form coloured compounds (Cu²⁺ blue, Fe²⁺ pale green, Fe³⁺ orange-brown, Cr³⁺ green, Mn²⁺ pink/colourless).
- Form ions with several different charges (variable oxidation states), e.g. Fe²⁺ and Fe³⁺; Cu⁺ and Cu²⁺.
- Useful as catalysts in industrial processes (e.g. iron in the Haber process; nickel in margarine production; vanadium oxide in the Contact process).
Comparison with Group 1 metals
| Property | Group 1 (e.g. Na) | Transition metal (e.g. Fe) |
|---|---|---|
| Hardness | Soft (cut with knife) | Hard |
| Density | Low (often <1 g/cm³) | High |
| Melting point | Low (Na 98 °C) | High (Fe 1538 °C) |
| Reactivity with water | Vigorous (Na fizzes, K ignites) | Slow (Fe rusts over months) |
| Compound colours | Colourless | Coloured |
| Ion charges | Always +1 | Variable (e.g. +2 and +3) |
| Catalytic activity | None typical | Common |
Variable oxidation states
A transition metal can lose different numbers of electrons depending on conditions, giving compounds with different formulae and often different colours:
- Iron(II) sulfate: FeSO₄ — pale green.
- Iron(III) sulfate: Fe₂(SO₄)₃ — orange-brown.
- Copper(I) oxide: Cu₂O — red-brown.
- Copper(II) oxide: CuO — black.
Roman numerals (I, II, III) show the charge in the compound.
Catalysts
A catalyst speeds up a reaction without being used up. Transition metals are excellent catalysts because:
- They can hold reactant molecules on their surface (large surface area in finely divided form).
- They can change oxidation state easily, providing alternative reaction pathways.
Famous examples:
- Iron — Haber process (N₂ + 3H₂ → 2NH₃).
- Nickel — hydrogenation of vegetable oils to make margarine.
- Vanadium(V) oxide — Contact process (production of sulfuric acid).
- Platinum — catalytic converters in cars.
Why transition metals form coloured compounds (extension)
The d-electrons absorb specific wavelengths of visible light, transmitting the rest. This is beyond GCSE — at GCSE you need to know that they form coloured compounds, but not the d-electron explanation.
⚠Common mistakes
- Saying all metals are transition metals. Group 1 and 2 metals are not.
- Saying transition metals are unreactive. They're less reactive than Group 1, but not inert (Fe rusts, Cu slowly corrodes).
- Forgetting variable oxidation states. This is the defining property to compare with Group 1.
Links
Builds on C1.5 (metal properties) and contrasts with C1.7 (Group 1). Catalysts come up in C6.3.
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