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 32a

Chapter 8, Problem 32a

(a) Based on the lattice energies of MgCl2 and SrCl2 given in Table 8.1, what is the range of values that you would expect for the lattice energy of CaCl2?

Verified step by step guidance

Identify the lattice energies of MgCl2 and SrCl2 from Table 8.1.

Understand that lattice energy is influenced by the size and charge of the ions involved.

Recognize that CaCl2 is between MgCl2 and SrCl2 in terms of ionic size, as calcium is between magnesium and strontium in the periodic table.

Use the trend in lattice energies from MgCl2 to SrCl2 to estimate the range for CaCl2, considering that smaller ions typically result in higher lattice energies.

Conclude that the lattice energy of CaCl2 should fall between the lattice energies of MgCl2 and SrCl2, based on the periodic trend and ionic sizes.

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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 in higher melting points and greater stability of the compound.

Trends in Lattice Energy

Lattice energy varies with the charge and size of the ions involved. Generally, as the charge of the ions increases, the lattice energy increases due to stronger electrostatic forces. Conversely, larger ions result in lower lattice energy because the distance between the ions increases, weakening the attraction.

Comparative Analysis

To estimate the lattice energy of CaCl2, one can compare it to the known lattice energies of MgCl2 and SrCl2. Since calcium (Ca) is positioned between magnesium (Mg) and strontium (Sr) in the periodic table, its lattice energy is expected to fall within the range defined by these two compounds, reflecting its ionic size and charge.

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Energy is required to remove two electrons from Ca to form Ca2+, and energy is required to add two electrons to O to form O2 - . Yet CaO is stable relative to the free elements. Which statement is the best explanation? (a) The lattice energy of CaO is large enough to overcome these processes. (b) CaO is a covalent compound, and these processes are irrelevant. (c) CaO has a higher molar mass than either Ca or O. (d) The enthalpy of formation of CaO is small. (e) CaO is stable to atmospheric conditions.

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List the individual steps used in constructing a Born–Haber cycle for the formation of BaI₂ from the elements. Which of the steps would you expect to be exothermic?

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Using Lewis symbols and Lewis structures, diagram the formation of SiCl4 from Si and Cl atoms, showing valence-shell electrons. e. How many bonding pairs of electrons are in the SiCl4 molecule?

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Textbook Question

Which of the following trends in lattice energy is due to differences in ionic radii: a. NaCl > RbBr > CsBr, b. BaO > KF, c. SrO > SrCl2?

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