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Chemistry

Catherine E. Housecroft, Edwin C. Constable

ISBN #9780273715450

4th Edition

995 Questions

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Summary

Learning Objectives

Key Concepts

Example Problems

Explanations

Common Mistakes

Summary

This section provides a deep dive into homonuclear covalent bonds, detailing methods for measuring internuclear distances and determining the covalent radii of atoms. It explains the concept of bond energy through the formation of diatomic molecules like H2, discusses bond enthalpies, the standard enthalpy of atomization, and outlines how to derive bond energies from standard heats of formation. Key takeaways include the importance of precise measurements and calculations in understanding molecular structure and reaction energetics.

Learning Objectives

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Key Concepts

CONCEPT

DEFINITION

Acyclic and cyclic alkanes

A discussion of both open?chain (acyclic) and ring (cyclic) saturated hydrocarbons, emphasizing their structural features, nomenclature, conformational behavior (including ring strain and conformation), and the processes used in their interconversion and synthesis.

Example Problems

Example 1

State what you understand by each of the following: (a) covalent radius; (b) bond dissociation enthalpy; and (c) the standard enthalpy of atomization of an element.

Example 2

Values of van der Waals radii $\left(r_{v}\right)$ and covalent radii $\left(r_{\mathrm{cov}}\right)$ for the elements from $Z=5$ to 9 are: (a) In which part of the periodic table are these elements? (b) Why is $r_{\mathrm{v}} > r_{\text {cov }}$ for each element? (c) Rationalize the trend in $r_{\mathrm{v}}$ values. (d) For $\mathrm{S}, r_{\mathrm{v}}=185 \mathrm{pm}$ and $r_{\mathrm{cov}}=103 \mathrm{pm} .$ How would you estimate these values experimentally?

Example 3

Using data from Appendix $6,$ estimate bond lengths for the gas phase diatomics $\mathrm{F}_{2}, \mathrm{Cl}_{2}, \mathrm{Br}_{2}$ and $\mathrm{I}_{2}$ Compare your answers with the values listed in Table $4.10 .$ Suggest reasons for the trend in bond lengths.

Example 4

(a) In an X-ray diffraction experiment, what causes the diffraction of the electromagnetic radiation? (b) Explain why X-ray diffraction results give a value of $103 \mathrm{pm}$ for the length of a localized 2 -centre 2-electron terminal B-H bond in the $\left[\mathrm{B}_{2} \mathrm{H}_{7}\right]^{-}$ ion (4.25) while the same bond is found to be $118 \mathrm{pm}$ in length from the results of a neutron diffraction experiment.

Example 5

The results of an electron diffraction experiment on a gaseous molecule $\mathrm{XF}_{3}$ give $\mathrm{X}$ - $\mathrm{F}$ distances of $131.3 \mathrm{pm}$ and $\mathrm{F}$ - $-\mathrm{F}$ separations of $227.4 \mathrm{pm}$ (a) What are the $\mathrm{F}-\mathrm{X}-\mathrm{F}$ bond angles? (b) Is the molecule planar or non-planar?

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Step-by-Step Explanations

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Common Mistakes

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