Book cover for Chemistry: The Molecular Nature of Matter

Chemistry: The Molecular Nature of Matter

Neil D. Jespersen, James E. Brady, Alison Hyslop

ISBN #9781118413920

7th Edition

3,064 Questions

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53,557 Students Helped

Homework Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

Chapter 21 provides a comprehensive look at metal complexes, emphasizing the formation of complex ions through coordinate covalent bonding and the classification of ligands. It covers essential nomenclature rules, coordination geometries, and the implications of crystal field theory for the properties of these complexes. Understanding the effects of ligand type, the chelate effect, and the various isomeric forms is crucial, especially given the real-world applications in biological systems. Overall, the chapter bridges fundamental chemical principles with practical examples in coordination chemistry.

Learning Objectives

1

Describe the formation of metal complexes via coordinate covalent bonding between metals and ligands.

2

Differentiate between monodentate, bidentate, and polydentate ligands and explain the chelate effect.

3

Apply the rules for writing complex ion formulas and proper nomenclature of metal complexes.

4

Analyze various coordination geometries and explain the role of crystal field theory in determining magnetic and optical properties.

5

Identify different isomers of metal complexes and discuss their real-world applications, particularly in biological systems.

Key Concepts

CONCEPT

DEFINITION

Complex Ion

An ion composed of a central metal atom or ion bonded to a surrounding array of molecules or anions (ligands) through coordinate covalent bonds.

Ligand

An ion or molecule that donates a pair of electrons to a metal ion to form a coordinate covalent bond.

Monodentate Ligand

A ligand that binds to a metal ion through a single donor atom.

Bidentate Ligand

A ligand that uses two donor atoms to form coordinate bonds with a metal ion, often creating a ring structure.

Polydentate Ligand

A ligand that can attach to a metal ion at multiple binding sites, forming chelate complexes.

Chelate Effect

The increased stability of a metal complex resulting from the formation of ring structures when polydentate ligands bind to a metal ion.

Coordination Geometry

The spatial arrangement of ligands around the central metal ion, which can vary (e.g., linear, tetrahedral, square planar, octahedral) based on the coordination number.

Crystal Field Theory

A model that explains the electronic structure, magnetic behavior, and optical properties of metal complexes by considering the effect of the electric field created by surrounding ligands.

Isomerism

The phenomenon where metal complexes with the same formula possess different arrangements of ligands or vary in spatial structure, leading to different chemical and physical properties.

Biological Metal Complexes

Metal complexes that play crucial roles in biological systems, such as enzyme function, oxygen transport, and electron transfer processes.

Example Problems

Example 1

The formation of the complex ion $\left[\mathrm{Cu}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$ is described as a Lewis acid-base reaction. Explain. (a) What are the formulas of the Lewis acid and the Lewis base in this reaction? (b) What is the formula of the ligand? (c) What is the name of the species that provides the donor atom? (d) What atom is the donor atom, and why is it so designated? (e) What is the name of the species that is the acceptor?

Example 2

To be a ligand, a substance should also be a Lewis base. Explain.

Example 3

Give two examples of a charged ligand and two examples of an uncharged ligand.

Example 4

Why are substances that contain complex ions often called coordination compounds?

Example 5

Use Lewis structures to diagram the formation of $\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}^{2+}$ and $\mathrm{CuCl}_{4}^{2-}$ ions from their respective components.
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Step-by-Step Explanations

QUESTION

How do you write the formula for a complex ion given the central metal, its oxidation state, and the surrounding ligands?

STEP-BY-STEP ANSWER:

Step 1: Identify the central metal ion and determine its oxidation state.
Step 2: List all ligands present, noting their types (monodentate, bidentate, or polydentate) and quantities.
Step 3: Arrange the ligands in alphabetical order (ignoring any prefixes like di-, tri-, etc.) when writing the complex formula.
Step 4: Combine the metal and ligands within square brackets and denote the overall charge of the complex outside the brackets.
Final Answer: The complex ion formula is correctly written with the metal, coordinated ligands in alphabetical order, and the net charge as determined by the oxidation state and ligand charges.

Writing Complex Ion Formulas

QUESTION

How is the coordination geometry of a metal complex determined based on its coordination number?

STEP-BY-STEP ANSWER:

Step 1: Count the number of ligand donor atoms directly bonded to the central metal ion to determine the coordination number.
Step 2: Refer to known geometries associated with specific coordination numbers (e.g., 2 = linear, 4 = tetrahedral or square planar, 6 = octahedral).
Step 3: Evaluate other factors such as electronic configuration and ligand steric effects which may favor one geometry over another.
Final Answer: By combining the coordination number with knowledge of common geometries and influencing factors, the most likely spatial arrangement of ligands is determined.

Determining Coordination Geometry

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Common Mistakes

  • Confusing the types of ligands (monodentate vs. polydentate) and not recognizing the significance of the chelate effect.
  • Improper ordering of ligands when writing the complex ion formula, leading to incorrect nomenclature.
  • Miscounting the coordination number by not accounting for all donor atoms in polydentate ligands.
  • Overlooking the impact of coordination geometry on the magnetic and optical properties of the metal complex.
  • Assuming all metal complexes have similar properties without considering isomerism and the influence of crystal field effects.