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 24b

Chapter 8, Problem 24b

NaCl and KF have the same crystal structure. The only difference between the two is the distance that separates cations and anions. (b) Use the ionic radii given in Figure 7.8 to estimate the Na─Cl and K─F distances.

Verified step by step guidance

Identify the ionic radii for Na^+ and Cl^- from Figure 7.8.

Identify the ionic radii for K^+ and F^- from Figure 7.8.

Add the ionic radius of Na^+ to the ionic radius of Cl^- to estimate the Na─Cl distance.

Add the ionic radius of K^+ to the ionic radius of F^- to estimate the K─F distance.

Compare the estimated distances to understand the difference in separation between the cations and anions in NaCl and KF.

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Key Concepts

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

Ionic Radii

Ionic radii refer to the effective size of an ion in a crystal lattice, which is influenced by its charge and the surrounding ions. Cations are typically smaller than their neutral atoms due to the loss of electrons, while anions are larger due to the gain of electrons. Understanding ionic radii is crucial for estimating distances between ions in ionic compounds.

Crystal Structure

Crystal structure describes the orderly arrangement of ions in a solid, which determines the properties of the material. In the case of NaCl and KF, both adopt a face-centered cubic lattice structure, where each ion is surrounded by six oppositely charged ions. This arrangement is essential for understanding how ionic distances are calculated based on the positions of cations and anions.

Ionic Bonding

Ionic bonding occurs when electrons are transferred from one atom to another, resulting in the formation of positively charged cations and negatively charged anions. The electrostatic attraction between these oppositely charged ions leads to the formation of ionic compounds like NaCl and KF. This concept is fundamental for understanding the interactions that dictate the distances between ions in a crystal lattice.

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Related Practice

Textbook Question

NaCl and KF have the same crystal structure. The only difference between the two is the distance that separates cations and anions. (a) The lattice energies of NaCl and KF are given in Table 8.1. Based on the lattice energies, would you expect the Na─Cl or the K─F distance to be longer?

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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?

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Textbook Question

(b) Write the chemical equation that represents the process of lattice energy for the case of NaCl.

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Textbook Question

(c) Would you expect salts like NaCl, which have singly charged ions, to have larger or smaller lattice energies compared to salts like CaO which are composed of doubly-charged ions?

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Textbook Question

The substances NaF and CaO are isoelectronic (have the same number of valence electrons). (b) What are the charges of each of the anions in each compound?

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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.

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