Transition Metals (Overview)

This lesson provides an overview of the transition metals, as required by AQA GCSE Combined Science Trilogy (8464, Chemistry 4.1.2). The transition metals are found in the central block of the periodic table, between Group 2 and Group 3. They include many commonly known metals such as iron, copper, gold, silver and zinc.

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Where Are the Transition Metals?

The transition metals occupy the large central block of the periodic table (sometimes called the d-block):

• They are positioned between Group 2 (alkaline earth metals) and Group 3 (the boron group).
• Common transition metals include: iron (Fe), copper (Cu), zinc (Zn), nickel (Ni), chromium (Cr), manganese (Mn), cobalt (Co), silver (Ag), gold (Au) and platinum (Pt).

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Typical Properties of Transition Metals

Compared to Group 1 metals, transition metals are much "harder" and more typically metallic:

Property	Transition Metals	Group 1 (Alkali Metals)
Melting point	Generally high (e.g. iron melts at 1538 °C)	Relatively low (e.g. sodium melts at 98 °C)
Density	Generally high	Relatively low (Li, Na, K float on water)
Hardness	Hard and strong	Very soft (can be cut with a knife)
Reactivity	Generally less reactive	Highly reactive

Additional Physical Properties

• Transition metals are good conductors of heat and electricity.
• They are malleable (can be hammered into shape) and ductile (can be drawn into wires).
• They have a shiny appearance.

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Special Properties of Transition Metals

The transition metals have several distinctive properties that set them apart:

1. Variable Oxidation States (Multiple Ion Charges)

Unlike Group 1 metals (which always form 1+ ions), transition metals can form ions with different charges:

Metal	Possible Ions	Example Compounds
Iron	$\text{Fe}^{2+}$Fe2+ and $\text{Fe}^{3+}$Fe3+	Iron(II) chloride $\text{FeCl}_2$FeCl2​; Iron(III) chloride $\text{FeCl}_3$FeCl3​
Copper	$\text{Cu}^{+}$Cu+ and $\text{Cu}^{2+}$Cu2+	Copper(I) oxide $\text{Cu}_2\text{O}$Cu2​O; Copper(II) sulfate $\text{CuSO}_4$CuSO4​
Manganese	$\text{Mn}^{2+}$Mn2+, $\text{Mn}^{4+}$Mn4+, $\text{Mn}^{7+}$Mn7+	Various compounds

Exam Tip: Roman numerals in compound names tell you the charge on the metal ion. For example, iron(III) chloride means the iron has a 3+ charge.

2. Coloured Compounds

Transition metal compounds are often coloured:

Compound	Colour
Copper(II) sulfate $\text{CuSO}_4$CuSO4​	Blue
Iron(II) sulfate $\text{FeSO}_4$FeSO4​	Green (pale)
Iron(III) chloride $\text{FeCl}_3$FeCl3​	Yellow/brown
Potassium dichromate $\text{K}_2\text{Cr}_2\text{O}_7$K2​Cr2​O7​	Orange
Potassium permanganate $\text{KMnO}_4$KMnO4​	Purple
Nickel(II) sulfate $\text{NiSO}_4$NiSO4​	Green

This contrasts with Group 1 compounds, which are typically white and dissolve to form colourless solutions.

3. Catalytic Activity

Many transition metals and their compounds act as catalysts — substances that speed up chemical reactions without being used up:

Catalyst	Reaction
Iron (Fe)	Haber process — making ammonia: $\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3$N2​+3H2​⇌2NH3​
Manganese(IV) oxide ($\text{MnO}_2$MnO2​)	Decomposition of hydrogen peroxide
Nickel (Ni)	Hydrogenation of vegetable oils (making margarine)
Platinum/Palladium	Catalytic converters in car exhausts
Vanadium(V) oxide ($\text{V}_2\text{O}_5$V2​O5​)	Contact process — making sulfuric acid

Exam Tip (AQA 8464): You must know at least one specific example of a transition metal used as a catalyst. Iron in the Haber process is the most commonly examined example.

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Comparison with Group 1 Metals

graph TD
    A["Comparison: Transition Metals vs Group 1"] --> B["Transition Metals"]
    A --> C["Group 1 — Alkali Metals"]
    B --> D["High melting points"]
    B --> E["Hard and dense"]
    B --> F["Form coloured compounds"]
    B --> G["Variable oxidation states"]
    B --> H["Good catalysts"]
    B --> I["Less reactive"]
    C --> J["Low melting points"]
    C --> K["Soft and low density"]
    C --> L["White compounds, colourless solutions"]
    C --> M["Always form 1+ ions"]
    C --> N["Not used as catalysts"]
    C --> O["Very reactive"]

    style A fill:#2c3e50,color:#fff
    style B fill:#3498db,color:#fff
    style C fill:#e67e22,color:#fff

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Coloured Compounds — A Key Identifier

One of the easiest ways to identify transition metal compounds is by their colour. In AQA exams, you may be asked to identify a metal ion based on the colour of its compound or solution:

Colour	Likely Metal Ion
Blue solution	$\text{Cu}^{2+}$Cu2+ (copper(II))
Pale green solution	$\text{Fe}^{2+}$Fe2+ (iron(II))
Orange/yellow solution	$\text{Fe}^{3+}$Fe3+ (iron(III))
Purple solution	$\text{Mn}^{7+}$Mn7+ (permanganate)
Green solid/solution	$\text{Ni}^{2+}$Ni2+ or $\text{Cr}^{3+}$Cr3+

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Worked Example

Question: Compare the properties of iron (a transition metal) with sodium (a Group 1 metal). (4 marks)

Answer:

1. Iron has a much higher melting point (1538 °C) than sodium (98 °C).
2. Iron is harder and denser than sodium (sodium is soft enough to cut with a knife).
3. Iron forms coloured compounds (e.g. green iron(II) sulfate, brown iron(III) chloride), while sodium compounds are white with colourless solutions.
4. Iron can form ions with different charges ($\text{Fe}^{2+}$Fe2+ and $\text{Fe}^{3+}$Fe3+), while sodium only forms Na⁺ ions.

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Why Are Transition Metals Less Reactive Than Group 1?

Transition metals do not lose their outer electrons as easily as Group 1 metals because:

• They have higher nuclear charges (more protons pulling on the electrons).
• Their electron arrangement provides less effective shielding for the outer electrons.
• More energy is needed to remove electrons from the atom.

This means they react less vigorously and do not react with cold water (unlike Group 1 metals).

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Common Mistakes

Mistake	Correction
Saying transition metals have low melting points	They generally have high melting points
Saying transition metals only form one type of ion	They form ions with variable charges (e.g. Fe²⁺ and Fe³⁺)
Confusing transition metals with Group 1	Group 1 metals are soft, low density and very reactive; transition metals are hard, dense and less reactive
Saying "iron chloride" without specifying the ion charge	You must say iron(II) chloride or iron(III) chloride
Forgetting that transition metals are catalysts	This is a key distinguishing property — you need at least one example

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Summary

• Transition metals are found in the central block of the periodic table between Groups 2 and 3.
• They have high melting points, high density and are hard and strong compared to Group 1 metals.
• They form coloured compounds (e.g. blue copper sulfate, green iron(II) sulfate).
• They can form ions with different charges (variable oxidation states).
• They are widely used as catalysts (e.g. iron in the Haber process).
• They are less reactive than Group 1 metals.
• They are good conductors of heat and electricity.

Exam Tip (AQA 8464): Comparison questions between transition metals and Group 1 metals are very common. Remember the key contrasts: melting point (high vs low), hardness (hard vs soft), density (high vs low), compounds (coloured vs white), ion charges (variable vs always 1+), reactivity (low vs high), and catalytic activity (yes vs no).

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What Combined Science Trilogy Actually Requires

On the AQA GCSE Combined Science: Trilogy (8464) specification, 5.1.3 Properties of transition metals is Triple-only content — it is not directly assessed on Trilogy papers. However, Trilogy students do need to be able to: