Transition ElementsCambridge IGCSE Chemistry: Revision notes

Section 1

What Are Transition Elements?

The transition elements are the block of metals found in the middle of the periodic table, between Group II and Group III.

They are all metals, and share several distinctive physical properties not typically seen together in Group I metals
Transition elements:
- have high densities
- have high melting points
- form coloured compounds
- often act as catalysts, both as elements and in their compounds

This makes them very different in character from the Group I alkali metals, which are soft, low-density, and low melting point.

Key termstransition elements

Example

Iron is used as a catalyst in the Haber process, and copper compounds are typically blue — both illustrate typical transition element behaviour.

Section 2

How Do Transition Elements Differ From Group I Metals?

Comparing transition elements with Group I alkali metals highlights what makes them distinctive:

Property	Group I (alkali metals)	Transition elements
Density	Low	High
Melting point	Low, decreasing down the group	High
Reactivity	Very reactive, increasing down the group	Much less reactive
Compounds formed	Usually white/colourless	Often coloured
Catalytic use	Not typically used as catalysts	Frequently used as catalysts

This contrast is a common way exam questions test understanding of both groups together.

Common mistake

Don't assume all metals behave like Group I metals — transition elements are far less reactive and much denser, which is why they are useful structurally (e.g. iron, copper) rather than being kept under oil like sodium and potassium.

Section 3

Why Do Transition Elements Have Variable Oxidation Numbers?

Unlike Group I or Group II metals, which almost always form ions with one fixed charge, transition elements can form ions with more than one oxidation number.

This is described as having variable oxidation numbers
A well-known example is iron, which can form iron(II) ions (Fe²⁺) or iron(III) ions (Fe³⁺)
The Roman numeral in a compound's name shows which oxidation number is present, e.g. iron(II) oxide contains Fe²⁺, while iron(III) oxide contains Fe³⁺
This ability to exist in different oxidation states is part of why many transition element compounds are useful in reactions involving oxidation and reduction

Key termsvariable oxidation number

Example

Iron(II) sulfate contains Fe2+ ions, while iron(III) sulfate contains Fe3+ ions — same metal, different oxidation number, different compound.

Section 4

How Can Position in the Periodic Table Help Predict Group Properties?

Just as trends can be identified within a group of typical elements (like Group I or Group VII), the position of any element in the periodic table can be used more generally to predict its likely properties.

If information is given about several elements in a group, a pattern (trend) can usually be identified and used to predict the properties of another element in that group
This skill applies across the periodic table, not just to the transition elements — but it is especially useful for elements not covered directly by the syllabus's named examples

Exam tip

When asked to 'predict' a property from a periodic table trend, look at the pattern in the given data and extend it logically — don't just guess.

Must Know

Transition elements are metals in the central block of the periodic table
They have high densities, high melting points, form coloured compounds, and often act as catalysts (as elements and in compounds)
They are much less reactive than Group I alkali metals, despite both being metals
Transition elements have variable oxidation numbers, e.g. iron forms both iron(II) and iron(III) ions
The Roman numeral in a compound name shows the oxidation number, e.g. iron(II) vs iron(III)
Position in the periodic table (group and period) can be used to predict an element's properties from known trends

That's the notes covered.

Carry on to the next subtopic.