Ch.7 - Covalent Bonding and Electron-Dot Structures

Problem 29

Chapter 7, Problem 29

Which of the following alkali metal halides has the largest lat-tice energy? Explain.(a) (b) (c)

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Identify the alkali metals and halides involved in each option (a), (b), and (c).

Understand that lattice energy is influenced by the charge of the ions and the distance between them. The greater the charge and the smaller the ionic radii, the stronger the lattice energy.

Recall that in the periodic table, as you move down a group, the ionic radius increases. This means that for alkali metals, the ionic radius increases from Li to Cs.

Similarly, for halides, the ionic radius increases as you move down the group in the periodic table, from F to I.

Compare the alkali metals and halides in each option based on their positions in the periodic table to determine which combination has the smallest ions with the highest charges, as this will likely have the largest lattice energy.

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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. Higher lattice energy indicates stronger ionic bonds, which typically results from smaller ionic radii and higher charges on the ions.

Ionic Size and Charge

The size of the ions involved in the formation of an ionic compound significantly affects lattice energy. Smaller ions can pack more closely together, leading to stronger electrostatic attractions and higher lattice energy. Additionally, the charge of the ions plays a crucial role; ions with higher charges will produce greater lattice energy due to stronger interactions.

Trends in Alkali Metal Halides

In alkali metal halides, lattice energy trends can be analyzed based on the alkali metal and halide involved. As you move down the group of alkali metals, the ionic size increases, leading to lower lattice energies. Conversely, halides with higher electronegativity (like fluorine) tend to form compounds with higher lattice energies due to their smaller ionic size compared to other halides.

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Use formal charge to select which resonance structure makes the largest contribution to the resonance hybrid. (LO 7.16) (a) Structure I (b) Structure II (c) Structure III (d) All structures are equivalent and make the same contri-bution to the resonance hybrid. (I)

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The following diagram shows the potential energy of two atoms as a function of internuclear distance. Match the descriptions with the indicated letter on the plot.(a) Repulsive forces are high between the two atoms. (b) The two atoms neither exert attractive nor repulsive forces on one another.(c) The attractive forces between atoms are maximized, resulting in the lowest energy state.(d) Attractive forces between atoms are present but are not at maximum strength.

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(b)