Ch.10 - Chemical Bonding I: The Lewis Model

Tro - Chemistry: A Molecular Approach 6th Edition

Tro6th EditionChemistry: A Molecular ApproachISBN: 9780137832217Not the one you use?Change textbook

Tro 6th Edition

Ch.10 - Chemical Bonding I: The Lewis Model

Problem 45

Chapter 10, Problem 45

Rubidium iodide has a lattice energy of -617 kJ/mol, while potassium bromide has a lattice energy of -671 kJ/mol. Why is the lattice energy of potassium bromide more exothermic than the lattice energy of rubidium iodide?

Verified step by step guidance

Understand the concept of lattice energy: Lattice energy is the energy released when ions in the gaseous state form an ionic solid. It is influenced by the charges of the ions and the distance between them.

Consider the charges of the ions: Both rubidium iodide (RbI) and potassium bromide (KBr) involve ions with charges of +1 and -1, so the charge factor is the same for both compounds.

Examine the sizes of the ions: Rubidium (Rb) and iodide (I) ions are larger than potassium (K) and bromide (Br) ions. Larger ions result in a greater distance between the centers of the ions in the lattice.

Apply Coulomb's Law: The lattice energy is inversely proportional to the distance between the ions. Since RbI has larger ions, the distance is greater, resulting in a less exothermic lattice energy compared to KBr.

Conclude the comparison: The smaller size of K and Br ions in KBr leads to a stronger attraction between the ions, resulting in a more exothermic lattice energy compared to RbI.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

Was this helpful?

Key Concepts

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

Lattice Energy

Lattice energy is the amount of 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. A more negative lattice energy indicates a more stable ionic compound, as it reflects a greater release of energy upon formation.

Ionic Size and Charge

The size and charge of the ions involved in an ionic compound significantly influence lattice energy. Smaller ions can pack more closely together, leading to stronger electrostatic attractions and higher lattice energy. Additionally, ions with higher charges produce stronger interactions, resulting in more exothermic lattice energies.

Comparative Analysis of Ionic Compounds

When comparing ionic compounds like rubidium iodide and potassium bromide, it is essential to consider the specific ions involved. Potassium (K+) and bromide (Br-) ions are smaller and have higher charge density compared to rubidium (Rb+) and iodide (I-), which contributes to the greater lattice energy of potassium bromide, making it more exothermic than rubidium iodide.

Recommended video:

Guided course

02:11

Ionic Compounds Naming

Related Practice

Textbook Question

Use Lewis symbols to determine the formula for the compound that forms between each pair of elements. a. Sr and P b. Ba and S c. Sr and Se d. Rb and I

Textbook Question

Write the Lewis symbols for the ions in each ionic compound. c. CaI₂

views

Textbook Question

The lattice energy of CsF is -744 kJ/mol, whereas that of BaO is -3029 kJ/mol. Explain this large difference in lattice energy.

Textbook Question

Arrange these compounds in order of increasing magnitude of lattice energy: CaO, NaBr, CsI, BaS.

Textbook Question

Use Lewis symbols to determine the formula for the compound that forms between each pair of elements. a. Mg and S b. Sr and Br c. K and Se d. Al and S

Textbook Question

Use the Born–Haber cycle and data from Appendix IIB, Chapter 9 and this chapter to calculate the lattice energy of LiBr. (ΔHsub for lithium is 138 kJ>mol.)