Structure and bonding · GCSE Chemistry
Transition metals
GCSE Chemistry revision on transition metals (Triple): coloured compounds, variable ions such as Fe²⁺ and Fe³⁺, catalysts, and comparison with Group 1 metals.
In the middle of the table: high melting points, hard, coloured compounds, more than one ion, good catalysts. Group 1 is the contrast — soft, white compounds, only 1+.
The important bits
What you need to know
- 1
Transition metals sit in the central block of the periodic table (Sc to Zn in Period 4). This is Triple / Chemistry-only on AQA; Combined Science does not require the full list of properties.
- 2
Compared with Group 1 they have higher melting points, higher densities and are harder and stronger. Iron, nickel and titanium are typical engineering metals.
- 3
They form ions with different charges: Fe²⁺ and Fe³⁺, Cu⁺ and Cu²⁺, Cr³⁺. The Roman numeral in copper(II) sulfate tells you Cu²⁺.
- 4
Many compounds are coloured: Cu²⁺(aq) is blue, Fe²⁺(aq) is pale green, Fe³⁺(aq) is yellow-brown, Ni²⁺ compounds are often green. Group 1 compounds are usually white.
- 5
They and their compounds are often catalysts: Fe in the Haber process, Ni in hydrogenation of alkenes, V₂O₅ in the contact process, MnO₂ for decomposition of hydrogen peroxide.
- 6
They still form metallic structures: positive ions in a sea of delocalised electrons, so they conduct heat and electricity and are malleable.
- 7
Copper, silver and gold are unreactive enough to be found native or easily extracted; iron is extracted in the blast furnace; they are not stored in oil like sodium.
- 8
Zn is often taught at the edge of the block. At GCSE, treat zinc as a metal that forms Zn²⁺, is used in galvanising, and is more reactive than iron but less than aluminium in the reactivity series you learn.
Quotations worth analysing
Short evidence. Real method.
“Fe²⁺ pale green(aq); Fe³⁺ yellow-brown(aq); Cu²⁺ blue(aq).”
The colour is a property of the ion in solution or in the compound. Iron(II) hydroxide is green; iron(III) hydroxide is brown. That is how you tell the ion in a precipitation test.
“N₂ + 3H₂ ⇌ 2NH₃ iron catalyst”
Iron provides an alternative pathway with lower activation energy. It is not used up. This is the same catalyst idea as in rates, with a named industrial example.
“Copper(II) sulfate is CuSO₄; iron(III) chloride is FeCl₃.”
Copper(II) is Cu²⁺, so with SO₄²⁻ the formula is CuSO₄. Iron(III) is Fe³⁺, so with Cl⁻ you need FeCl₃. The numeral is the charge, not the number of atoms of the metal.
Go deeper
Compare with Group 1 in a table, then attach a reason
Group 1: one ion (1+), white compounds, soft, low melting points, very reactive with water. Transition metals: variable ions, coloured compounds, hard, high melting points, much less reactive with water (iron rusts slowly; sodium explodes). The metallic bonding in transition metals involves more delocalised electrons and a stronger attraction to the positive ions, which helps explain hardness and melting point at GCSE. You do not need d-orbitals. You do need two named differences and one example each. If the paper is Combined, skip this page; if it is Chemistry Paper 1, this comparison is a likely six-mark.
Go deeper
Variable charge is a formula skill
Iron(II) oxide is FeO because Fe²⁺ and O²⁻. Iron(III) oxide is Fe₂O₃ because two Fe³⁺ cancel three O²⁻. Copper(I) oxide is Cu₂O; copper(II) oxide is CuO. Students write FeO₃ or Cu₂SO₄ without checking charge. Name the ion, write the charge, then balance as in the ions-and-formulae page. In displacement, a more reactive metal still reduces the ion: Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s), and the blue colour fades as Cu²⁺ is used up. That is reactivity series meeting transition-metal colour. Iron(III) chloride is FeCl₃, not FeCl₂ — the numeral is the charge.
Go deeper
Catalysts are a use, not a magic extra
A catalyst provides an alternative pathway with lower activation energy and is not used up. Transition metals are good at this, which is why the Haber process, margarine manufacture and catalytic converters appear here as well as in rates. Catalytic converters use platinum, palladium and rhodium to convert CO, NOₓ and unburnt hydrocarbons into CO₂, N₂ and H₂O. Link the metal to the reaction; do not write “it speeds it up” without the activation-energy sentence if the command word is explain. Nickel catalyses hydrogenation of alkenes: same definition, different named process.
See the idea in action
A green solution of iron(II) sulfate is left in air and turns yellow-brown. Fe²⁺ is oxidised to Fe³⁺. Iron(II) hydroxide precipitated with sodium hydroxide is green and also darkens as Fe³⁺ forms. Formulae: FeSO₄ contains Fe²⁺; Fe₂(SO₄)₃ contains Fe³⁺. Compared with sodium sulfate, which is white and contains only Na⁺, this colour change is typical transition-metal chemistry. Iron can also catalyse the Haber process; sodium cannot be used that way.
Exam technique
Turn knowledge into marks
Flag this as Triple / Chemistry-only. In answers, name two differences from Group 1 (colour, variable charge, hardness, melting point, catalyst) with a specific ion or process. Use Roman numerals in names to show the charge.
Common mistakes
Do not give these marks away
- 01
Writing this content in a Combined Science paper, or saying all metals form coloured compounds.
- 02
Using the Roman numeral as a subscript, for example writing copper(II) sulfate as Cu₂SO₄.
- 03
Claiming transition metals are stored in oil, or that they only form 1+ ions.
Which property is typical of transition metals but not of Group 1 metals?
AThey form only 1+ ions
BTheir compounds are often coloured and they can act as catalysts
CThey are stored in oil and fizz in water
DThey are monatomic gases
Show the answer
Their compounds are often coloured and they can act as catalysts. Transition metals form variable ions, coloured compounds and useful catalysts. Group 1 metals form colourless 1+ compounds and are too reactive to use as industrial catalysts in that way.
Quick questions
If this is the bit you searched
Are transition metals on Combined Science GCSE Chemistry?
The detailed properties (coloured compounds, variable oxidation states, catalysts) are Chemistry-only / Triple on AQA. Combined Science still uses metals such as iron and copper in the reactivity series.
Why are transition metal compounds coloured?
Many transition-metal ions absorb some visible light. Cu²⁺(aq) looks blue, Fe²⁺(aq) pale green and Fe³⁺(aq) yellow-brown. Group 1 compounds are usually white.
What does copper(II) mean in copper(II) sulfate?
The copper ion is Cu²⁺. With sulfate SO₄²⁻ the formula is CuSO₄. The Roman numeral is the charge on the metal ion.
Name a transition metal catalyst and its process.
Iron in the Haber process (N₂ + 3H₂ ⇌ 2NH₃), nickel in hydrogenation of alkenes, or manganese(IV) oxide for the decomposition of hydrogen peroxide.