# Transition metals form coloured compounds, whereas compounds of Group 1 metals are white solids that dissolve to give colourless solutions. Explain why transition metal compounds are coloured and describe two other characteristic properties of transition metals that distinguish them from Group 1 metals.

> Edexcel A-Level Chemistry (9CH0) — 15.1 Transition metal chemistry · Explain · 5 marks

> Transition metals occupy the central block of the periodic table between Group 2 and Group 3. Unlike Group 1 metals such as sodium and potassium, transition metals display a distinctive set of chemical and physical properties.

## Mark scheme (5 marks)

1. Transition metals have partially filled d-orbitals / d sub-shells (accept: d electrons that can absorb certain frequencies/wavelengths of visible light)
2. The absorption of certain frequencies of visible light by d electrons causes the compound to appear coloured (the complementary colour is seen)
3. Transition metals can form ions with more than one stable oxidation state / variable oxidation states (correct example required for the mark, e.g. iron can form Fe²⁺ and Fe³⁺ / copper can form Cu⁺ and Cu²⁺)
4. Transition metals and their compounds act as catalysts (correct named example required, e.g. iron in the Haber process, manganese dioxide in the decomposition of hydrogen peroxide, vanadium pentoxide in the Contact process)
5. Transition metals have high melting points / high densities / high tensile strength compared to Group 1 metals (any one of these, correctly stated as a comparison or contrast with Group 1)

## Key terms

- [transition metals](https://www.gradenine.co.uk/glossary/transition-metals)

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](https://www.gradenine.co.uk/learn)
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