Book cover for Chemistry The Science in Context

Chemistry The Science in Context

Thomas R. Gilbert

ISBN #9780393615142

5th Edition

2,675 Questions

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191,124 Students Helped

Homework Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

This chapter provides an in-depth exploration of transition metals, emphasizing the formation and properties of complex ions and coordination compounds. It covers key areas including the naming conventions of these compounds, the significance of the chelate effect through polydentate ligands, and offers a detailed look into crystal field theory to explain coloration, magnetic behavior, and spin states. The chapter also bridges theory with practice by discussing vital biological functions and medical applications, highlighting how these chemical principles are applied in enzyme catalysis, nutrient transport, diagnostic imaging, and targeted cancer therapies.

Learning Objectives

1

Understand the formation, structure, and properties of complex ions and coordination compounds.

2

Apply naming conventions and IUPAC rules to accurately name coordination compounds.

3

Explain the chelate effect and the role of polydentate ligands in enhancing complex stability.

4

Analyze crystal field theory to interpret colors, magnetic behavior, and spin states in transition metal complexes.

5

Evaluate the biological and medical applications of transition metal complexes, including enzyme function, nutrient transport, diagnostic imaging, and cancer therapy.

Key Concepts

CONCEPT

DEFINITION

Transition Metals

Elements that have partially filled d orbitals, which exhibit unique chemical behaviors including variable oxidation states and complex formation.

Coordination Compound

A chemical compound consisting of a central metal ion bonded to surrounding molecules or anions called ligands.

Complex Ion

An ion that consists of a central metal atom or ion surrounded by an array of bound ligands, carrying an overall charge.

Polydentate Ligands

Ligands that can attach to a metal ion at multiple binding sites, forming ring-like structures within the complex.

Chelate Effect

The enhanced stability of a metal complex that forms when a polydentate ligand binds to a metal ion, compared to equivalent monodentate ligands.

Crystal Field Theory

A model that describes the breaking of degeneracies of electron orbital states, primarily in transition metal complexes, due to the presence of ligands.

Magnetic Behavior and Spin States

Characteristics of metal complexes determined by the distribution of electrons in split d-orbitals, leading to high-spin or low-spin configurations that affect magnetic properties.

Isomerism in Coordination Compounds

The phenomenon where complexes with the same formula have different spatial arrangements of atoms, resulting in distinct physical and chemical properties.

Example Problems

Example 1

Two of the four highlighted elements in Figure P22.1 have cations that form colored compounds with $\mathrm{Cl}^{-}$. Which ones?

Example 2

Which of the highlighted transition metals in Figure P22.2 form $\mathrm{M}^{2+}$ cations that cannot have high-spin and low-spin states? (FIGURE CAN'T COPY)

Example 3

Which of the highlighted transition metals in Figure $\mathrm{P} 22.2$ have $\mathrm{M}^{2+}$ cations that form colorless tetrahedral complex ions?

Example 4

Smoky quartz has distinctive lavender and purple colors due to the presence of manganese impuritics in crystals of silicon dioxide. Which of the orbital diagrams in Figure $\mathrm{P} 22.4$ best describes the $\mathrm{Mn}^{2+}$ ion in a tetrahedral field?

Example 5

Chelation Therapy 1 The compound with the structure Ehown in Figure $\mathrm{P} 22.5$ is widely used in chelation therapy to remove excessive lead or mercury in paticnts exposed to these metals. How many electron-pair-donor groups ("teeth") does the sequestering agent have when the carboxylic acid groups are ionized? (FIGURE CAN'T COPY)
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Step-by-Step Explanations

QUESTION

How would you name the coordination compound [Fe(CN)6]4- using IUPAC conventions?

STEP-BY-STEP ANSWER:

Step 1: Identify the central metal ion. Here, Fe is the central atom.
Step 2: Determine the oxidation state of the metal. In this complex, the overall charge is -4 and each cyanide (CN) ligand carries a -1 charge, implying that Fe is in the +2 oxidation state.
Step 3: Rename the ligands according to IUPAC rules. For cyanide, use the name 'cyanido'.
Step 4: Arrange ligands in alphabetical order (ignoring prefixes that denote quantity) and add the appropriate numerical prefix if needed.
Final Answer: The compound is named 'hexacyanidoferrate(II)'.

Naming Coordination Compounds

QUESTION

How does the crystal field splitting energy (Δ) relate to the observed color in a metal complex?

STEP-BY-STEP ANSWER:

Step 1: Recognize that when ligands approach the metal ion, they cause a splitting of the d-orbitals into two energy levels (commonly labeled as t2g and eg in an octahedral field).
Step 2: The energy difference between these split levels is defined as the crystal field splitting energy, Δ.
Step 3: This gap corresponds to the energy of light absorbed when electrons are excited from a lower energy level to a higher one.
Step 4: The color observed is the complementary color of the absorbed light wavelength.
Final Answer: The value of Δ determines which wavelength of light absorbed, thereby influencing the color displayed by the metal complex.

Crystal Field Splitting and Color

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Common Mistakes

  • Incorrectly assigning oxidation states or misidentifying ligands during the naming process.
  • Confusing monodentate and polydentate ligand behavior, leading to a misunderstanding of the chelate effect.
  • Overlooking the interplay between crystal field splitting and both color and magnetic properties in transition metal complexes.
  • Failing to properly differentiate between various types of isomerism in coordination compounds.