6.2.1 General Properties of Transition Metals

What Are Transition Metals?

Transition metals, specifically those from titanium ($Ti$) to copper ($Cu$), are defined by their ability to form stable ions with an incomplete $d$-sublevel. This incomplete $d$-sublevel leads to several characteristic properties that distinguish them from other elements in the periodic table.

Key Properties of Transition Metals

Complex Formation

Transition metals readily form complex ions. In these complexes, a central metal ion binds to surrounding molecules or ions called ligands through coordinate bonds. These ligands donate lone pairs of electrons to the metal ion, stabilizing various complex structures.

Formation of Coloured Ions

One of the most striking features of transition metals is their ability to form coloured ions in solution.

These colours arise from the electronic transitions within the $d$-sublevel, where electrons absorb specific wavelengths of visible light, causing them to jump between different energy levels.

The specific colour depends on the metal ion, its oxidation state, and the ligands attached to it.

Variable Oxidation States

Transition metals can exhibit multiple oxidation states, often differing by a single electron. This variability arises from the close energy levels of the $4s$ and $3d$ orbitals, allowing for different numbers of electrons to be lost or shared in reactions.

This property is significant for redox reactions and the diverse chemistry of transition metals.

Catalytic Activity

Many transition metals and their compounds act as catalysts in chemical reactions. They provide alternative reaction pathways with lower activation energies, allowing reactions to proceed faster. This catalytic activity is often due to their ability to change oxidation states and form complexes that can facilitate the making and breaking of chemical bonds.

Electronic Configurations of Transition Metals

General Configuration

The electronic configurations of transition metals explain many of their properties.

A general configuration is

$$[\text{Ar}]3d^{x}4s^{2}$$

But there are exceptions:

Exceptions

Chromium ($Cr$):

$$1\text{s}^22\text{s}^22\text{p}^63\text{s}^23\text{p}^63\text{d}^54\text{s}^1$$

Instead of:

$$3\text{d}^44\text{s}^2$$

A half-filled $3d$ sub-level provides extra stability.

Copper ($Cu$):

$$1\text{s}^22\text{s}^22\text{p}^63\text{s}^23\text{p}^63\text{d}^{10}4\text{s}^1$$

Instead of:

$$3\text{d}^94\text{s}^2$$

A fully filled $3d$ sub-level is more stable.