Transition metals

Many transition elements have ions with different charges, form coloured compounds and are useful as catalysts.

Ions with Different Charges: Many transition elements can form ions with different positive charges (oxidation states). Group 1 metals, in contrast, almost always form only a +1 ion.

• Examples:

  • Iron can form Fe²⁺ (iron(II)) and Fe³⁺ (iron(III)) ions.

  • Copper can form Cu⁺ (copper(I)) and Cu²⁺ (copper(II)) ions.

  • Chromium (Cr) can form Cr²⁺, Cr³⁺, and Cr⁶⁺ ions.

  • Manganese (Mn) can form Mn²⁺, Mn³⁺, Mn⁴⁺, Mn⁶⁺, and Mn⁷⁺ ions.

  • Cobalt (Co) can form Co²⁺ and Co³⁺ ions.

  • Nickel (Ni) can form Ni²⁺ and Ni³⁺ ions (though Ni²⁺ is more common).

Coloured Compounds: Many compounds of transition metals are coloured, both as solids and in solution. This is a striking difference compared to Group 1 compounds, which are usually white solids and form colourless solutions.

• Examples:

  • Copper(II) compounds are often blue (e.g., copper(II) sulfate solution).

  • Iron(II) compounds are typically pale green (e.g., iron(II) sulfate solution).

  • Iron(III) compounds are typically brown or orange (e.g., iron(III) chloride solution).

  • Chromium(III) compounds are often green or violet.

  • Potassium manganate(VII) (containing Mn⁷⁺) is a vibrant purple solution.

  • Nickel(II) compounds are often green.

Useful as Catalysts: Many transition metals and their compounds are useful as catalysts – substances that speed up a chemical reaction without being used up themselves. Their ability to form ions with different charges contributes to this catalytic activity.

• Examples:

  • Iron (Fe) is used as a catalyst in the Haber process (the industrial production of ammonia).

  • Nickel (Ni) is used as a catalyst in the hydrogenation of alkenes (converting carbon-carbon double bonds to single bonds).

  • Vanadium(V) oxide (V₂O₅) (a compound of vanadium, a transition metal) is used as a catalyst in the Contact process (the industrial production of sulfuric acid).