Transition Elements – IGCSE Chemistry Definition

Transition elements are tested mainly through comparison with alkali metals. The examiner wants you to list their distinctive properties — coloured compounds, variable oxidation states, catalytic activity — and contrast these with Group I. This is a reliable 3–4 mark question on Paper 2 or Paper 4.

The 0620 definition

The transition elements (also called transition metals) are the block of metallic elements found between Groups II and III in the periodic table. Examples include iron (Fe), copper (Cu), zinc (Zn), manganese (Mn), nickel (Ni), and chromium (Cr).

Key properties

Property	Transition elements	Group I metals (comparison)
Melting point	High (Fe: 1538 °C)	Low (Na: 98 °C)
Density	High (Fe: 7.9 g/cm³)	Low (Na: 0.97 g/cm³)
Hardness	Hard, strong	Soft (cut with knife)
Reactivity	Relatively low	Very high
Ion charges	Variable (Fe²⁺ / Fe³⁺)	Fixed (+1 only)
Compound colour	Coloured	White / colourless
Catalytic activity	Often catalysts	Not catalysts

Coloured compounds

Ion	Colour
Cu²⁺	Blue
Fe²⁺	Green (pale)
Fe³⁺	Orange-brown / yellow-brown
Cr³⁺	Green
Mn²⁺	Very pale pink
MnO₄⁻	Purple

These colours are directly useful in qualitative analysis — the colour of a solution often tells you which transition metal ion is present.

Variable oxidation states (Supplement)

Transition elements can form ions with different charges. Iron is the most important example:

• Iron(II) = Fe²⁺ (found in FeSO₄, which is green)
• Iron(III) = Fe³⁺ (found in FeCl₃, which is yellow-brown)

This is why transition metal compounds are named with Roman numerals: copper(II) sulfate, iron(III) chloride.

Catalytic activity

Many industrial processes use transition metal catalysts:

• Iron in the Haber process (N₂ + 3H₂ ⇌ 2NH₃)
• Manganese(IV) oxide in decomposition of hydrogen peroxide
• Nickel in hydrogenation of vegetable oils
• Vanadium(V) oxide in the Contact process

Worked exam question

Describe three differences between the properties of transition elements and Group I elements. [3]

Mark scheme

Any three from: transition elements have higher melting points [1]; higher density [1]; form coloured compounds (Group I form white/colourless) [1]; have variable oxidation states / more than one ion charge (Group I form +1 only) [1]; can act as catalysts [1]; are harder / stronger [1]; are less reactive [1]

Common exam mistakes

• Listing “transition elements are metals” as a difference — Group I elements are metals too.
• Forgetting the Roman numeral in compound names when the element has variable oxidation states — writing “iron chloride” instead of “iron(III) chloride”.
• Including zinc in examples of coloured compounds — Zn²⁺ compounds are actually white or colourless.