Question

Briefly define each term. \begin{equation}\begin{array}{l}{\text { a) coordination number }} \\ {\text { b) ligand }} \\ {\text { c) bidentate and polydentate }} \\ {\text { d) complex ion }} \\ {\text { e) chelating agent }}\end{array} \end{equation}\

Short answer

a) Coordination number is the count of ligand atoms bonded to a metal ion. b) Ligand is a molecule or ion that binds to a metal atom. c) Bidentate ligands bind with two atoms, while polydentate provide multiple pairs of electrons. d) Complex ion is a metal ion with ligands attached by coordinate bonds. e) Chelating agents are substances that can form multiple bonds with a singular metal ion.

Step-by-step solution

Define Coordination Number

The coordination number is the number of ligand atoms which are directly bonded to the central metal ion in a complex.

Define Ligand

A ligand is an ion or molecule that binds to the central metal atom to form a coordination complex. It can contribute one or more pairs of electrons to the metal.

Define Bidentate and Polydentate

Bidentate ligands are ligands that can donate two pairs of electrons from two different atoms to a central metal ion. Polydentate ligands (also known as multidentate or chelating ligands) can donate multiple pairs of electrons to the central metal ion.

Define Complex Ion

A complex ion is a species formed from a central metal ion bonded to one or more ligands that have donated electrons to the metal ion, creating a coordinate covalent bond.

Define Chelating Agent

A chelating agent is a substance whose molecules can form several bonds to a single metal ion. Chelating agents are usually organic compounds and are often used to sequester metal ions from solution.

Key concepts

Coordination Number

In coordination chemistry, the coordination number represents how various ligands are arranged around a central metal ion. This number specifically points to the count of donor atoms attached to the metal, which can vary widely depending on the metal ion and ligands involved. For instance, a coordination number of six suggests a metal ion is surrounded by six ligands' donor atoms. This concept is crucial as it influences the geometry and binding properties of complex ions—forming structures that can be octahedral, tetrahedral, or square planar, among others. Understanding coordination numbers is fundamental in predicting the stability and reactivity of coordination complexes in various chemical and biological systems.

Ligand

Ligands are the cornerstone of coordination complexes. Acting as Lewis bases, these ions or molecules offer one or more pairs of electrons to the central metal ion, which is typically a Lewis acid. Ligands can range from simple ions, like chloride, to more complex organic molecules. Each ligand that forms a bond with the metal ion contributes to the overall properties of the complex. This could affect the complex's color, solubility, and even biological activity. Ligands are not just passive spectators; they actively participate in the myriad of functions that coordination compounds can perform in areas like catalysis, material science, and medicine.

Bidentate Ligands

Among ligands, bidentate types are unique. They have two atoms which can each donate an electron pair to the central metal, allowing for the formation of ring structures within the complex. This can increase the stability of the complex through a phenomenon known as chelate effect.

Polydentate Ligands

Polydentate ligands, also known as chelating agents, offer even greater stability as they contain multiple pairs of donating atoms. These agents can form several bonds simultaneously, firmly anchoring the metal ion at the center of the complex.

Complex Ion

The term 'complex ion' refers to a charged entity made up of a metal ion at its core and one or more ligands bound to it through coordinate covalent bonds. These ions can have a positive, negative, or neutral charge. They are not to be confused with simple ions, which are typically formed by electron loss or gain without involving coordinate bonds. Complex ions are prevalent in solutions and are responsible for a multitude of chemical reactions such as metal extraction, biological enzyme functions, and even the color displays in fireworks. Their charge and composition play a significant role in determining the pathways of reactions involving coordination compounds.

Chelating Agent

Chelating agents, with their multi-dentate natures, are adept at securely binding metal ions through multiple ligand atoms. This 'claw-like' binding aptly derives from the Greek word 'chele,' meaning claw. These agents are particularly important in both industrial applications — such as removing unwanted metals from solutions or as additives in medicines to ensure proper metal ion concentrations in the body — and in nature, where they can help transport metal ions or detoxify metals. By forming stable, ring-shaped complexes, they are stronger binders than their monodentate counterparts. This unique ability makes chelating agents extremely valuable in a variety of scientific fields, including biomedical and environmental sciences.