General properties of transition metals

Chemistry· 21.1· 20 min read

1. Definition and Electron Configuration★★☆☆☆⏱ 5 min

📘 Definition

Transition Metal

IUPAC definition: A transition metal is an element with a partially filled d subshell in at least one of its stable ions. All transition metals are d-block elements, but not all d-block elements are transition metals.

Example:

Iron (Fe) is a transition metal; scandium ( $S c^{3 +}$ : $3 d^{0}$ ) and zinc ( $Z n^{2 +}$ : $3 d^{10}$ ) are d-block but not transition metals.

For the first row of transition metals (period 4, groups 3 to 12), the 4s orbital fills before the 3d orbitals. When transition metals form ions, they lose 4s electrons first before losing 3d electrons.

📐 Worked Example

Show that copper meets the definition of a transition metal. Neutral copper has electron configuration $[A r] 3 d^{10} 4 s^{1}$ .

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Step 1: Write the electron configuration of copper's most common ion, $C u^{2 +}$
2
$[Ar] 3d^9 4s^0$
3
Step 2: Check for a partially filled d subshell in any common ion
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While $C u^{+}$ has a full $3 d^{10}$ subshell, $C u^{2 +}$ has 9 out of 10 d-electrons, so it is partially filled.
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Since at least one common ion has a partially filled d subshell, copper is classified as a transition metal.

2. Physical Properties★★☆☆☆⏱ 4 min

All transition metals share typical metallic properties, but have distinct traits compared to s-block metals of the same period:

High melting and boiling points: Strong metallic bonding from delocalized s and d electrons requires more energy to break.
High density and hardness: Smaller atomic radii and closer atomic packing compared to s-block metals lead to higher density.
Good electrical and thermal conductivity: Delocalized free electrons enable efficient charge and energy transfer.
Malleability and ductility: Non-directional metallic bonding allows atoms to slide past each other without breaking the lattice.

📐 Worked Example

Explain why vanadium (melting point 1910 °C) has a much higher melting point than potassium (melting point 63.5 °C), both in period 4.

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Step 1: Compare the strength of metallic bonding
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Vanadium is a transition metal with 5 delocalized valence electrons ( $3 d^{3} 4 s^{2}$ ), compared to 1 delocalized electron for potassium ( $4 s^{1}$ ). Vanadium also has a much smaller atomic radius than potassium.
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The attraction between positive metal ions and delocalized electrons is much stronger for vanadium.
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Step 2: Relate bonding strength to melting point
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Stronger metallic bonding requires more energy to break the lattice, resulting in a much higher melting point for vanadium.

3. Variable Oxidation States★★★☆☆⏱ 6 min

📘 Definition

Variable Oxidation State

The ability of transition metals to form stable compounds with multiple different oxidation states, a key characteristic that distinguishes them from most main group metals.

Variable oxidation states arise because the 3d and 4s orbitals in first row transition metals have very similar energy levels. This means that different numbers of electrons can be lost during ionization without a large, energetically prohibitive jump in ionization energy.

📐 Worked Example

Vanadium forms common stable ions with oxidation states +2, +3, +4 and +5. Explain why all these oxidation states are energetically accessible.

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Step 1: Neutral vanadium electron configuration: $[A r] 3 d^{3} 4 s^{2}$ . 4s electrons are lost first when forming ions:
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$V^{2+}: [Ar] 3d^3$
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$V^{3+}: [Ar] 3d^2$
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$V^{4+}: [Ar] 3d^1$
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$V^{5+}: [Ar] 3d^0$
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Step 2: The energy required to remove each additional 3d electron is very similar, so no ionization step has an excessively high energy requirement. This is unique to transition metals due to the similar energy of 3d and 4s orbitals, so all oxidation states form stable compounds.

✓ Quick check

Check your understanding:

Why do transition metals have variable oxidation states?
- A. Their 3d and 4s orbitals have similar energy
- B. They have more protons than main group metals
- C. They form complex ions easily
- D. Their atomic radius is smaller than main group metals
Reveal answer
A —
Correct! The similar energy of 3d and 4s orbitals means removing different numbers of electrons does not require an excessively large energy input.

4. General Chemical Properties★★★☆☆⏱ 5 min

Transition metals share several key chemical properties that result from their electron structure and variable oxidation states:

Formation of coloured compounds: Partially filled d subshells allow d-d electron transitions that absorb visible light, producing coloured compounds.
Ability to act as catalysts: Variable oxidation states allow easy electron transfer, making transition metals and their compounds effective catalysts.
Formation of stable complex ions: Small, highly charged transition metal ions can accept lone pairs from ligands to form stable coordinate bonds.

📐 Worked Example

Iron is used as a heterogeneous catalyst in the Haber process. Explain why iron is an effective catalyst for this reaction.

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Step 1: Transition metal catalysts rely on variable oxidation states to facilitate reaction
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Iron has multiple accessible oxidation states (+2, +3, etc.), allowing it to donate and accept electrons from reactant molecules adsorbed onto its surface.
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This weakens the bonds in reactant molecules (e.g. $N_{2}$ and $H_{2}$ ), lowering the activation energy for the reaction.
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Step 2: After the reaction, iron returns to its original oxidation state and surface structure, so it remains unchanged and can catalyze further reaction cycles.

5. Common Pitfalls

Wrong move:

Claiming all d-block elements are transition metals.

Why:

Scandium and zinc are d-block but have no common ions with partially filled d subshells.

Correct move:

Use the IUPAC definition, and exclude scandium and zinc from classification as transition metals.

Wrong move:

Saying transition metals lose 3d electrons before 4s electrons when forming ions.

Why:

Despite 3d filling before 4s in neutral atoms, 4s electrons are higher energy and lost first.

Correct move:

Always remove all 4s electrons first, then remove 3d electrons to write the ion electron configuration.

Wrong move:

Thinking melting point increases consistently along the first transition series.

Why:

Melting point depends on the number of delocalized d electrons, peaking around groups 5-6.

Correct move:

Remember melting point rises to a peak around vanadium/chromium then decreases across the series.

Wrong move:

Confusing oxidation number with the number of d electrons lost.

Why:

All 4s electrons are lost first, so oxidation number equals the total number of electrons lost from 4s and 3d.

Correct move:

Always remove 4s electrons first, then remove additional electrons from 3d to match the oxidation state.

6. Quick Reference Cheatsheet

Property	Key Point
Definition	Partially filled d subshell in ≥1 common ion
Exceptions (not transition metals)	Scandium ( $S c^{3 +} : 3 d^{0}$ ), Zinc ( $Z n^{2 +} : 3 d^{10}$ )
Physical properties	High MP/BP, high density, good conductivity
Variable oxidation states	Similar energy of 3d/4s orbitals enables multiple stable states
Key chemical properties	Coloured compounds, catalytic activity, complex formation

7. Frequently Asked

Why is zinc not classified as a transition metal?

Zinc has a full $3 d^{10}$ subshell in all its common ions ( $Z n^{2 +}$ ), so it does not meet the IUPAC definition of a transition metal, despite being a d-block element.

Why are transition metals harder than s-block metals?

Transition metals have higher charge density and delocalized d-electrons, leading to stronger metallic bonding than group 1 and 2 s-block metals, resulting in higher melting points and greater hardness.

When this came up on past exams

AI-estimated based on syllabus patterns — cross-check with official past papers for accuracy. Use only as revision-focus signals.

2022 · 12
Identify transition metals from a list
2023 · 22
Explain variable oxidation state origin
2021 · 11
Compare properties of Ca and Fe

Going deeper

syllabusCIE 9701 2025-2026 SyllabusCheck section 21.1 for full requirements

What's Next

Understanding the general properties of transition metals is the foundation for all further topics in A-level transition element chemistry, from coloured complexes to redox titrations. The core concepts you learned here, especially the IUPAC definition, variable oxidation states and the role of d orbitals, underpin all the reactions and properties you will study next. This topic is frequently tested in both multiple choice and structured questions, so it is critical to master the core definitions and key properties before moving on to more complex applications. Common exam questions ask you to compare transition metal properties to s-block main group metals, so remember the key distinctions we covered in this module.