Transition Metals: Variable Oxidation States, Coloured Ions, and Complexes

Overview of Transition Metals

Transition metals, found in the d-block of the periodic table, are known for their unique properties, including variable oxidation states, formation of coloured ions, and ability to form complex compounds.

In this section, we will focus on the transition metals from Scandium (Sc) to Zinc (Zn).

Variable Oxidation States

• Definition: Transition metals can exhibit multiple oxidation states, meaning they can lose different numbers of electrons.
• Reason: This is due to the similar energy levels of their 3d and 4s orbitals, allowing for various electron configurations.
• Examples:
  • Iron (Fe) can exist in +2 and +3 oxidation states.
  • Manganese (Mn) can exhibit oxidation states from +2 to +7.

Coloured Ions

Transition metals often form coloured ions due to d-d electron transitions. When light hits these ions, certain wavelengths are absorbed, and the complementary colour is observed.

• Example: The ion $$\text{Cu}^{2+}$$ is blue in solution.
• Example: The ion $$\text{Cr}^{3+}$$ is green in solution.

Complex Formation

Transition metals can form complex ions, which are central metal ions bonded to surrounding molecules or ions, called ligands.

• Coordination Number: The number of ligand bonds to the central metal ion. Commonly 4 or 6.
• Example: $$\text{[Fe(CN)}_6\text{]}^{3-}$$ is a complex ion with a coordination number of 6.