What are transition elements?
The transition elements occupy the central block of the periodic table (Groups 3–12), between Group 2 and Group 13. Common examples include iron (Fe), copper (Cu), zinc (Zn), manganese (Mn) and chromium (Cr). They are all hard, strong metals with high melting and boiling points and high densities.
Special chemical properties
Transition elements differ from Group 1 and 2 metals in several important ways:
- Variable oxidation states (valencies): e.g. iron forms Fe2+ and Fe3+; copper forms Cu+ and Cu2+.
- Coloured compounds: e.g. Cu2+ is blue, Fe2+ is pale green, Fe3+ is brown.
- Catalytic activity: e.g. iron in the Haber process, vanadium(V) oxide in the Contact process.
- Form complex ions and are often used as coloured pigments.
Key idea
Transition elements show variable oxidation states, form coloured compounds, and act as catalysts — properties not shown by typical Group 1 or 2 metals.
Worked example
Iron(II) sulfate solution is pale green while iron(III) chloride solution is brown. This colour difference is used to identify the oxidation state of the iron ion present, showing how transition metals form coloured ions in different oxidation states.
Remember
- Central block, hard, dense, high melting points.
- Variable oxidation states (e.g. Fe²⁺/Fe³⁺).
- Coloured compounds; act as catalysts.