Chemistry: The Central Science (13th Edition)

Published by Prentice Hall
ISBN 10: 0321910419
ISBN 13: 978-0-32191-041-7

Chapter 8 - Basic Concepts of Chemical Bonding - Exercises - Page 335: 8.21c

Answer

The lattice energy of salts composed of doubly-charged ions like $CaO$ is larger than that of salts composed of singly-charged ions like $NaCl$.

Work Step by Step

The attraction between 2 opposite-charged ions can be described by Coulomb's law. Here the electrostatic potential energy of 2 interacting charged bodies is $$E_{el}=\frac{kQ_1Q_2}{d}$$ $k$: Coulomb's law constant $Q_1$: the magnitude of charge of body 1 $Q_2$: the magnitude of charge of body 2 $d$: the distance between 2 bodies' centers Therefore, the attraction between 2 opposite-charged ions depends on the magnitude of charges of both bodies. In other words, the higher the magnitude of charges of 2 bodies, the stronger the attraction between them. We also know that lattice energy is the energy required to remove a solid ionic compound, which is held by electrostatic attraction, into gaseous ions. So the magnitude of lattice energy depends on the magnitude of attraction among ions. Eventually, we can conclude that the magnitude of lattice energy depends on the magnitude of charges of the bodies (particles) in the compound: the higher the magnitude of charges of the particles, the stronger the attraction among them, the larger the lattice energy of the compound. Salts like $CaO$ are composed of doubly-charged ions, so the magnitude of charges of the ions are much higher than that of the ions of salts like $NaCl$, which are composed of singly-charged ions. Therefore, the lattice energy of salts composed of doubly-charged ions like $CaO$ is larger than that of salts composed of singly-charged ions like $NaCl$.
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