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Ch.9 - Chemical Bonding I: The Lewis Model
Chapter 9, Problem 44

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?

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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 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.
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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.
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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.
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