Question

Describe what a complex ion is and give an example.

Short answer

A complex ion is a metal ion bonded to ligands; e.g., hexaaquacopper(II) ion \\([Cu(H_2O)_6]^{2+}\).

Step-by-step solution

Introduction to Complex Ions

A complex ion is a type of chemical species consisting of a central metal ion bonded to one or more molecules or ions known as ligands. These ligands donate electron pairs to form coordinate covalent bonds with the metal ion, resulting in a stable structure.

Understand the Components

In a complex ion, the central metal ion is usually a transition metal, which means it can accept electrons in its d orbitals from the ligands. The ligands are usually molecules or ions like water, ammonia, or chloride ions, which have lone pairs of electrons.

Formation of Complex Ions

The formation of complex ions occurs through a process called complexation, where the ligands bond to the metal ion. This bonding is described as coordinate covalent bonding because the ligands donate both electrons needed for the bond, as opposed to sharing electrons equally.

Example of a Complex Ion

An example of a complex ion is the hexaaquacopper(II) ion, written as \[ \text{[Cu(H}_2\text{O)}_6]^{2+} \]. Here, copper is the central metal ion (Cu^{2+}), and it is surrounded by six water molecules acting as ligands, donating electron pairs to the copper ion.

Key concepts

Coordinate Covalent Bonding

Coordinate covalent bonding is a special type of chemical bonding. Unlike regular covalent bonds, where each atom supplies one electron to form a bond, coordinate covalent bonds have both electrons provided by one atom. This atom is typically a ligand with available lone electron pairs.
In the context of complex ions, the central metal ion often has empty orbitals that can accept electrons. This allows ligands to donate electron pairs, forming stable arrangements.

• Coordinate covalent bonding is essential for the stability of complex ions.
• Allows for the formation of various geometrical structures depending on the number and type of ligands involved.

This type of bonding results in unique properties and complex shapes, affecting how these species interact with other chemical entities.

Transition Metal Complexes

Transition metal complexes are fascinating structures involving transition metals bonded with ligands. Transition metals, such as iron, copper, or nickel, possess d orbitals that can readily accept electrons.
The unique ability of these metals to exist in various oxidation states makes them suitable centers for complex ion formation. They enable the creation of colourful and varied complexes, often used in catalysis and material science.

• They have variable oxidation states, making them versatile in forming complexes.
• The availability of d orbitals facilitates diverse bonding environments.

These complexes can alter physical properties like colour and solubility due to their formation and structure.

Ligands in Chemistry

Ligands are crucial components in the chemistry of complex ions. A ligand is any ion or molecule that can donate a pair of electrons to a metal ion. This process is known as coordination.
Ligands can be small molecules like water or larger organic compounds. They define the properties and reactivity of the resulting complex ion by determining its overall geometry and electron distribution.

• There are various types of ligands, including monodentate, bidentate, and polydentate, depending on how many coordination sites they have.
• Examples include water, ammonia, chloride ions, and complex organic molecules like EDTA.

Choosing the right ligand can tailor complexes for specific functions, making ligands a flexible and inventive aspect of coordination chemistry.