Inorganic Chemistry: Transition Metals

Introduction to Transition Metals

Transition metals are found in Groups 3-12 on the Periodic Table.
They have a unique ability to use their d orbitals during chemical bonding, which gives rise to their varied and often colourful compounds.
Most transition metals are hard, high-density, high-melting and high-boiling substances, due to their strong metallic bonds.

Transition metals often have several oxidation states because they can lose different numbers of d-electrons.
They can form complex ions with other ions or molecules, often resulting in coordinated bonding.
Transition metals and their compounds are often catalysts due to their ability to provide a site for reactant molecules to meet and react.

A complex ion has a metal ion at its centre with a number of other molecules or ions surrounding it. These can be considered as ligands.
Ligands are molecules or ions that donate a pair of electrons to a transition metal to form a coordinate bond.
The ligands and metal ion together form the complex ion, which can often show colour-due to d-d transitions involving their d-electrons.

Oxidation states in transition metals are often positive because they involve the loss of electrons.
The maximum oxidation state is typically equal to the number of unpaired electrons in the outer d subshell.
Some transition metals like copper, iron, and manganese can exist in more than one oxidation state, which contributes to their versatility in acting as catalysts.

Transition metals provide a surface for a reaction to take place. They increase the speed of the reaction by lowering the activation energy.
Transition metals and their compounds are important catalysts in industrial processes such as the Haber process where iron is used to catalyse the production of ammonia.
Catalysts are not used up in the reaction so they’re economically beneficial to use in various industrial processes.

Many transition metal ions are coloured due to the absorption of certain wavelengths of light which results in an electronic transition within the d orbitals.
The precise energy gap between the lower and higher d orbitals, and thus the colour observed, can be affected by the type of ligand and the oxidation state of the metal.
Colour change is often associated with changes in oxidation state, such as when potassium manganate(VII) (purple) is reduced to manganese(II) ion (colourless).

Transition metals have several applications, such as in the construction of structures, manufacturing of aircraft, production of steel and other alloys, and in catalysts in various chemical reactions.
They also play vital roles in biological systems. For instance, iron is a key component of haemoglobin in blood, and copper and zinc are important for enzymatic reactions.