Book cover for General Chemistry: Principles and Modern Applications

General Chemistry: Principles and Modern Applications

Ralph H. Petrucci, F. Geoffrey Herring, Jeffry D. Madura, Carey Bissonnette

ISBN #9780132931281

11th Edition

3,230 Questions

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293,395 Students Helped

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

This chapter provides a comprehensive overview of complex ions and coordination compounds. It introduces Werner’s groundbreaking theory, explores various types of ligands and their binding modes, and covers the nomenclature and isomerism that dictate the structures of these compounds. The role of crystal field theory in explaining the magnetic and spectral properties of complexes is emphasized, along with discussions on complex-ion equilibria and acid–base reactions. Overall, the chapter builds a foundation for understanding the chemical behavior and practical applications of coordination compounds in various fields including catalysis, materials science, and medicine.

Learning Objectives

1

Explain Werner’s theory of coordination compounds and its historical significance in inorganic chemistry.

2

Identify and classify various types of ligands and understand their binding modes in complex ions.

3

Describe the nomenclature, isomerism, and coordination geometries encountered in complex ions.

4

Apply crystal field theory to analyze the bonding, magnetic properties, and color of coordination compounds.

5

Examine the equilibrium and acid–base behavior of complex ions and relate these concepts to real-world applications.

Key Concepts

CONCEPT

DEFINITION

Coordination Compound

A chemical species consisting of a central metal atom or ion bonded to surrounding ligands through coordinate covalent bonds.

Werner’s Theory

An early theory of coordination compounds proposed by Alfred Werner that distinguishes between primary (ionic) and secondary (coordinate) valencies in metal complexes.

Ligand

An ion or molecule that donates at least one pair of electrons to a central metal atom or ion to form a coordinate covalent bond within a complex.

Isomerism in Coordination Compounds

The phenomenon where coordination compounds with the same formula have different arrangements of ligands, resulting in structural or stereoisomers.

Crystal Field Theory

A model that describes the breaking of degeneracies of metal ion d-orbitals due to an electrostatic field produced by surrounding ligands, influencing the color and magnetic properties of complexes.

Complex-Ion Equilibria

The dynamic equilibrium between complex ions and their constituent metal ions and ligands in solution, which can be affected by factors such as pH and ligand concentration.

Example Problems

Example 1

Write the formula and name of (a) a complex ion having $\mathrm{Cr}^{3+}$ as the central ion and two $\mathrm{NH}_{3}$ molecules and four $\mathrm{Cl}^{-}$ ions as ligands (b) a complex ion of iron(III) having a coordination number of 6 and $\mathrm{CN}^{-}$ as ligands (c) a coordination compound comprising two types of complex ions: one a complex of $\mathrm{Cr}(\mathrm{III})$ with ethylenediamine (en), having a coordination number of 6 the other, a complex of $\mathrm{Ni}(\mathrm{II})$ with $\mathrm{CN}^{-}$, having a coordination number of 4

Example 2

What are the coordination number and the oxidation state of the central metal ion in each of the following complexes? Name each complex. (a) $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}$ (b) $\left[\mathrm{AlF}_{6}\right]^{3-}$ (c) $\left[\mathrm{Cu}(\mathrm{CN})_{4}\right]^{2-}$ (d) $\left[\mathrm{CrBr}_{2}\left(\mathrm{NH}_{3}\right)_{4}\right]^{+}$ (e) $\left[\operatorname{Co}(\text { ox })_{3}\right]^{4-}$ (f) $\left[\mathrm{Ag}\left(\mathrm{S}_{2} \mathrm{O}_{3}\right)_{2}\right]^{3-}$

Example 3

Supply acceptable names for the following: (a) $\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right] \mathrm{Cl}$ (b) $\left[\mathrm{Cu}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{SO}_{4}$ (c) $\mathrm{PtCl}_{2}(\mathrm{en})$ (d) $\left[\mathrm{CrBr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5}\right]^{2+}$ (e) $\operatorname{Rb}\left[\mathrm{AgF}_{4}\right]$ (f) $\mathrm{Na}_{2}\left[\mathrm{Fe}(\mathrm{CN})_{5} \mathrm{NO}\right]$

Example 4

Write appropriate formulas for the following. (a) potassium hexacyanidoferrate(III) (b) bis(ethylenediamine)copper(II) ion (c) pentaaquahydroxidoaluminum(III) chloride (d) amminechloridobis(ethylenediamine) chromium(III) sulfate (e) tris(ethylenediamine)iron(III) hexacyanidoferrate(II)

Example 5

Draw Lewis structures for the following ligands: (a) $\mathrm{H}_{2} \mathrm{O}$ (b) $\mathrm{CH}_{3} \mathrm{NH}_{2}$ (c) ONO (d) SCN
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Step-by-Step Explanations

QUESTION

How does Werner's theory distinguish between the primary and secondary valencies in a coordination compound?

STEP-BY-STEP ANSWER:

Step 1: Identify the central metal ion and its oxidation state, which corresponds to the primary valency (ionic character).
Step 2: Recognize that the secondary valency is associated with the number and type of ligands coordinated to the metal, forming the coordination sphere.
Step 3: Understand that primary valency is similar to the usual valency seen in ionic compounds, while the secondary valency follows the coordination number and describes the geometry of the complex.
Step 4: Conclude that Werner’s theory explains complex formation by segregating these two types of valencies, providing insight into the structure and reactivity of coordination compounds.
Final Answer: Werner’s theory differentiates between the primary valency (oxidation state) and the secondary valency (coordination number and spatial arrangement of ligands), helping to rationalize the structure of complex ions.

Understanding Werner’s Theory

QUESTION

How does crystal field theory explain the color observed in a coordination complex?

STEP-BY-STEP ANSWER:

Step 1: Recognize that in a coordination complex, the approach of ligands creates an electrostatic field that splits the degenerate d-orbitals of the central metal ion into groups with different energy levels.
Step 2: Understand that the energy difference between these split d-orbitals (Δ) determines the wavelengths of light absorbed by the complex.
Step 3: Identify that the absorbed light corresponds to the promotion of electrons from the lower-energy orbitals to the higher-energy ones.
Step 4: Conclude that the complementary color of the absorbed wavelength is what is observed in the complex.
Final Answer: The color of a coordination complex is explained by crystal field theory through the splitting of d-orbitals; the specific energy gap leads to absorption of certain wavelengths, and the observed color is the complement of the absorbed light.

Applying Crystal Field Theory

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Common Mistakes

  • Confusing the roles of primary and secondary valencies in coordination compounds.
  • Mixing up the oxidation state of the metal with the coordination number.
  • Overlooking the importance of ligand field strength, which affects orbital splitting and properties such as color and magnetism.
  • Incorrectly applying nomenclature rules, particularly when distinguishing between similar isomers.
  • Neglecting the dynamic nature of complex-ion equilibrium in solution, which can lead to errors in predicting reaction outcomes.