Ionic Bonding (Section)(a) Does the lattice energy of an

Chapter 5, Problem 24E

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QUESTION:

(a) Does the lattice energy of an ionic solid increase or decrease (i) as the charges of the ions increase, (ii) as the sizes of the ions increase?

(b) Arrange the following substances not listed in Table 8.2 according to their expected lattice energies, listing them from lowest lattice energy to the highest: MgS, KI, GaN, LiBr.

Table 8.2 Lattice Energies for Some Ionic Compounds

\(\begin{array}{llll} \text { Compound } & \begin{array}{l} \text { Lattice Energy } \\ (\mathbf{k J} / \mathbf{m o l}) \end{array} & \text { Compound } & \begin{array}{l} \text { Lattice Energy } \\ (\mathbf{k J} / \mathbf{m o l})
\end{array} \\ \hline \mathrm{LiF} & 1030 & \mathrm{MgCl}_{2} & 2326 \\ \mathrm{LiCl} & 834 & \mathrm{SrCl}_{2} & 2127 \\ \mathrm{Lil} & 730 & & \\ \mathrm{NaF} & 910 & \mathrm{MgO} & 3795 \\ \mathrm{NaCl} & 788 & \mathrm{CaO} & 3414 \\ \mathrm{NaBr} & 732 & \mathrm{SrO} & 3217 \\ \mathrm{NaI} & 682 & & \\ \mathrm{KF} & 808 & \mathrm{ScN} & 7547 \\ \mathrm{KCl} & 701 & & \\ \mathrm{KBr} & 671 & & \\ \mathrm{CsCl} & 657 & & \\ \mathrm{CsI} & 600 & & \\ \hline \end{array}\)

Questions & Answers

QUESTION:

(a) Does the lattice energy of an ionic solid increase or decrease (i) as the charges of the ions increase, (ii) as the sizes of the ions increase?

(b) Arrange the following substances not listed in Table 8.2 according to their expected lattice energies, listing them from lowest lattice energy to the highest: MgS, KI, GaN, LiBr.

Table 8.2 Lattice Energies for Some Ionic Compounds

\(\begin{array}{llll} \text { Compound } & \begin{array}{l} \text { Lattice Energy } \\ (\mathbf{k J} / \mathbf{m o l}) \end{array} & \text { Compound } & \begin{array}{l} \text { Lattice Energy } \\ (\mathbf{k J} / \mathbf{m o l})
\end{array} \\ \hline \mathrm{LiF} & 1030 & \mathrm{MgCl}_{2} & 2326 \\ \mathrm{LiCl} & 834 & \mathrm{SrCl}_{2} & 2127 \\ \mathrm{Lil} & 730 & & \\ \mathrm{NaF} & 910 & \mathrm{MgO} & 3795 \\ \mathrm{NaCl} & 788 & \mathrm{CaO} & 3414 \\ \mathrm{NaBr} & 732 & \mathrm{SrO} & 3217 \\ \mathrm{NaI} & 682 & & \\ \mathrm{KF} & 808 & \mathrm{ScN} & 7547 \\ \mathrm{KCl} & 701 & & \\ \mathrm{KBr} & 671 & & \\ \mathrm{CsCl} & 657 & & \\ \mathrm{CsI} & 600 & & \\ \hline \end{array}\)

ANSWER:

Step 1 of 3

(a) Here, we are going to explain the factors that are affecting the Lattice energy.

Lattice energy: It is the energy required to completely separate one mole of a solid ionic compound into its gaseous ions.

\(\mathrm{NaCl}(s)\rightarrow\mathrm{Na}^+(aq)+\mathrm{Cl}^-(aq)\ H_{\text{lattice }}=+788\mathrm{\ kJ}/\mathrm{mol}\)

The magnitude of the lattice energy of an ionic solid depends on the charges of the

ions, their sizes, and their arrangement in the solid.

\(E=\frac{k Q_{1} Q_{2}}{d}\)

Where,

Q1 and Q2 are the charges on the particles in Coulombs, with their signs; d is the distance between their centers in meters, and k is a constant.

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