Ch.8 - Basic Concepts of Chemical Bonding

Brown - Chemistry: The Central Science 15th Edition

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Brown 15th Edition

Ch.8 - Basic Concepts of Chemical Bonding

Problem 28

Chapter 8, Problem 28

Which of the following trends in lattice energy is due to differences in ionic radii: a. NaCl > RbBr > CsBr, b. BaO > KF, c. SrO > SrCl2?

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Identify the concept of lattice energy, which is the energy required to separate one mole of an ionic solid into its gaseous ions.

Understand that lattice energy is influenced by the charge of the ions and the distance between them, which is related to the ionic radii.

Recognize that smaller ionic radii result in stronger attractions between ions, leading to higher lattice energies.

Compare the ionic radii of the ions in each pair: NaCl vs. RbBr vs. CsBr, BaO vs. KF, and SrO vs. SrCl2.

Determine which trend in lattice energy is primarily due to differences in ionic radii by considering the size of the ions involved in each comparison.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Lattice Energy

Lattice energy is the energy released when gaseous ions combine to form an ionic solid. It is a measure of the strength of the forces between the ions in an ionic compound. Higher lattice energy indicates stronger ionic bonds, which typically results from smaller ionic radii and higher charges on the ions.

Ionic Radii

Ionic radii refer to the size of ions in a crystal lattice. The size of an ion affects the distance between the centers of the ions in a lattice, influencing the lattice energy. Generally, smaller ions lead to stronger attractions and higher lattice energies due to their closer proximity in the lattice structure.

Trends in Ionic Compounds

Trends in ionic compounds often relate to the size and charge of the ions involved. For example, as you move down a group in the periodic table, ionic radii increase, which typically decreases lattice energy. Understanding these trends helps predict the relative lattice energies of different ionic compounds based on their constituent ions.

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Related Practice

Textbook Question

Energy is required to remove two electrons from Ca to form Ca2+, and energy is required to add two electrons to O to form O2 - . Yet CaO is stable relative to the free elements. Which statement is the best explanation? (a) The lattice energy of CaO is large enough to overcome these processes. (b) CaO is a covalent compound, and these processes are irrelevant. (c) CaO has a higher molar mass than either Ca or O. (d) The enthalpy of formation of CaO is small. (e) CaO is stable to atmospheric conditions.

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Textbook Question

The substances NaF and CaO are isoelectronic (have the same number of valence electrons). (d) Using the lattice energies in Table 8.1, predict the lattice energy of ScN.

Textbook Question

(a) Does the lattice energy of an ionic solid increase or decrease (i) as the charges of the ions increase, (ii) as the sizes of the ions increase?

Textbook Question

Consider the ionic compounds KF, NaCl, NaBr, and LiCl. (a) Use ionic radii (Figure 7.8) to estimate the cation–anion distance for each compound.

Textbook Question

List the individual steps used in constructing a Born–Haber cycle for the formation of BaI₂ from the elements. Which of the steps would you expect to be exothermic?

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Textbook Question

Use data from Appendix C, Figure 7.11, and Figure 7.13 to calculate the lattice energy of KI.